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Air Brake ManualWorking with drivers to make our roads safer.
ForewordThe Air Brake Manual has been prepared by Manitoba Public Insurance, to assist drivers in understanding the basic operation and function of an air brake system. The study of this manual, together with practical instruction, is recommended for a driver who is preparing for the air brake examination. A large illustration of a complete dual air brake system is located on the inside cover and can be folded out and referred to when studying this manual. Study questions are included at the end of each section so that readers may self–test their understanding of the subject matter. Drivers who have qualified and are authorized to operate air brake equipped vehicles are encouraged to review this manual on a periodic basis to ensure they are fully aware of the proper method of inspecting an air brake system and identifying problems that can occur when the system malfunctions.
The illustrations and explanations of various types of brake system designs are provided for instructional purposes only. Most air gauges measure in imperial units. Therefore the measurements used and relating to the air brake system will be in imperial units. This manual has no legislative sanction. For interpreting and applying the law, consult The Drivers and Vehicles Act, The Highway Traffic Act and its regulations. Sales of this manual are final and not refundable.
We gratefully acknowledge the contributions of all jurisdictions, particularly British Columbia.
i
Air Brake Endorsement• Permits the holder to drive vehicles
equipped with air brakes in class of vehicle for which the driver is licenced.
• To adjust manual or automatic slack adjusters, the operator must hold an “S” brake endorsement.
Requirements for Air Brake Endorsement• Must complete an Air Brake Written Test.
• Must complete an Air Brake Practical Test.
An air brake endorsement is not required for a licensed holder to drive a Class 3 or 5 air brake equipped vehicle if it is registered as a farm vehicle. Class 3 or 5 air brake equipped vehicles, fitted with dealer plates, may be driven by farmers for demonstration purposes.
Use of Licence as a Learner PermitA holder of any licence may be authorized to operate vehicles equipped with air brakes as a learner after meeting the required written standards. The learner must be supervised by someone who has held, for at least two years, an air brake endorsement.
ii
Dual Air Brake System
1 2 3 4 5 6 7 8 9 10 11
11 1223242526282729
31
3332
34
iii
30
6 6
12 13 14 15
16
17
6
18 15141920212212
1. Compressor 2. Governor 3. Air dryer 4. Safety valve 5. Supply/wet reservoir 6. Drain valves 7. One–way check valves 8. Primary/dry reservoir 9. Low pressure indicator 10. Secondary/dry reservoir 11. Rear service brake chambers 12. Spring parking brake chambers 13. Tractor relay valves 14. Trailer service brake chamber 15. Trailer spring parking brake chamber 16. Trailer reservoirs 17. Trailer relay valve 18. Trailer spring brake valve 19. Anti–compound lines 20. Glad hands
21. Supply (emergency) line 22. Control (service) line 23. Spring brake modulator valve 24. Tractor protection valve 25. Stop lamp switch 26. Two–way check valves 27. Spring parking brake control valve 28. Trailer supply valve 29. Reservoir air pressure gauges 30. Trailer brake hand valve 31. Foot valve 32. Front service brake chambers 33. Quick release valve 34. Automatic front brake limiting valve
This illustration has an automatic front brake limiting valve (34), and therefore the control valve (35), for a manual front brake limiting valve (36) are not shown here, but appear later in the manual.
Legend
blue–supply/wet
green–primary/dry
red–secondary/dry
yellow–spring parking
brake system
dark green–trailer system
In–cab portion is
highlighted
CHECK THE SLACK!
It is up to YOU,
the DRIVER,
to ensure that
your vehicle has
safe, properly
adjusted brakes.
1 • Air Brake Manual
Table of Contents
Foreword Foldout i AirBrakeEndorsement Foldout iiRequirementsforAirBrakeEndorsement Foldout iiUseofLicenceasaLearnerPermit Foldout ii DualAirBrakeSystemIllustration Foldout iiiHowtoBookYourTestAppointment 3KeyPointsAboutYourTests 4
Section 1—Brakes and Braking 5
Heat–Energy–Traction–Friction 6Speed–Weight–Distance 7BrakingForce 7UseofAirPressure 8LeverageandAirPressure 8StoppingDistance 8SectionSummaryQuestions 9
Section 2—The Componentsof an Air Brake System 11
TheComponentsofanAirBrakeSystem 12 CompressorandGovernor 12 Reservoirs 14 AirDryer 15 SafetyValve 16 FootValve 16 BrakeChambers,SlackAdjusters andBrakeLining 16 WedgeBrakes 20 DiscBrakes 21 Air–Over–HydraulicBrakeSystems 21 Air–Actuated–HydraulicBrakeSystem 21 Air–Boost–HydraulicBrakeSystem 22 SectionSummaryQuestions 24
Section 3—How the Basic System Works 25
BasicAirBrakeSystem 26 One–wayCheckValve 26 AirPressureGauge 27 BrakeApplicationGauge 27 LowPressureWarningDevice 27 StopLightSwitch 27 QuickReleaseValve 28 RelayValve 28 ManualFrontBrakeLimitingValve 28 AutomaticFrontBrakeLimitingValve 29 TandemRearAxles 30 SectionSummaryQuestions 30
Section 4—Spring Parking Brakes 31
SpringParkingBrakeSystems 32 UsingaSpringParkingBrake 33 MechanicalRelease(Caging) 35 SectionSummaryQuestions 35
Section 5—Trailer System 37
GladHands 38 ApplicationLine 38 TrailerBrakeHandValve 39 Two–wayCheckValves 40 TractorProtectionSystem 41 TractorProtectionValve 42 TrailerSupplyValve 43 AutomaticTrailerSupplyValveSystem 44 TractorandTrailerCoupled 46 ChargingtheTrailerSystem 47 FootorHandValveBrakeApplication 47 EmergencyApplication 48 Supply(Emergency)LineRupture 49 Control(Service)LineRupture 49 LossofReservoirAirPressure 50 ManualTrailerSupplyValve 51 TrailerSpringParkingBrakes 52 SectionSummaryQuestions 52
1 Air Brake Manual
2 • Air Brake Manual
Section 6—Dual Air Brake System 53
BasicDualAirBrakeSystem 54 DualAirBrakeSystemwith SpringParkingBrakes 56 SpringParkingBrakeswithModulatorValve 57 CombinationTractorandTrailer
withSpringParkingBrakes 58SectionSummaryQuestions 59
Section 7—Electronic ControlledBraking and Traction Systems 61
Anti–lockBrakeSystem(ABS) 62 AutomaticTractionControl(ATC) 64 SectionSummaryQuestions 64
Section 8—Brake Adjustment and In–Service Check 65
BrakeAdjustment 66 BrakeAdjustment—It’sCritical 66 BrakeAdjustment—It’stheLaw 66 Definition 67 CheckingandAdjustingS–CamBrakes —ManualSlackAdjusters 69 PryMethodofFreeStrokeMeasurement 69 AppliedStrokeMethod (servicebrakeapplication) 70 BrakeAdjustmentIndicators 70 BrakeAdjustment—ManualSlackAdjuster 71 Adjustment 71 AdjustingS–CamBrakeswithAutomatic SlackAdjusters—Why—When—How 72 EmergencyManualBrakeAdjustment —AutomaticSlackAdjusters 73 DiscBrakeAdjustment 75 WedgeBrakeAdjustment 75 AfteraBrakeAdjustment 75 In-ServiceChecks 76 MaintenanceandServicing oftheAirBrakeSystem 76 AirBrakeAdjustmentMyths 77 SectionSummaryQuestions 78
Section 9—Pre–Trip and Post–Trip Air Brake Inspection 79
VehicleInspection 80 AirBrakePracticalTest 80 Pre–TripInspection—CombinationUnit 81 BrakeAdjustment—CombinationUnit 82 Post–TripInspection—CombinationUnit 84 Pre–TripInspection—SingleUnit 85 BrakeAdjustment—SingleUnit 86 Post–TripInspection—SingleUnit 87 Pre–TripInspection—Air–Over–Hydraulic (AirActuated)BrakeSystem 88 Post–TripInspection—Air–Over–Hydraulic (AirActuated)BrakeSystem 89 SectionSummaryQuestions 89
MetricConversionTable 89Pre-tripInspectionTearOutSheet 91OrganandTissueDonation 93
Test Appointments How to Book Your Knowledge or Road Test
1 Visit any Autopac agent* to pay for your test and to schedule your test appointment.
2 The agent can provide you details of available appointments at any testing location.
3 You can schedule your test appointment up to eight weeks in advance.
Test Locations
Winnipeg• 15 Barnes Street (at Bison Drive) • 40 Lexington Park (at Gateway Road) • 1284 Main Street • 930 St. Mary’s Road (French Language Services available) • 125 King Edward Street East • 1103 Pacific Avenue • 420 Pembina Highway
Outside Winnipeg• Arborg | 323 Sunset Boulevard• Beausejour | 848 Park Avenue • Brandon | 731–1st Street • Dauphin | 217 Industrial Road • Portage la Prairie | 25 Tupper Street• Selkirk | 1008 Manitoba Avenue • Steinbach | 165 Park Road West, Unit 2, Clearspring Village Mall• Thompson | 53 Commercial Place • Winkler | 355 Boundary Trail
Mobile Test UnitsMobile Test Units serve rural customers living outside Service Centre communities. Locations and schedules are available from any Autopac agent.
*For a list of Autopac agents, see mpi.mb.ca.
Key Points About Your Tests
Cost*• A knowledge test costs $10.• Costs for road tests: • Class 1 licence: $50 • Class 5 licence: $30 • Class 2 or 3 licence: $45 • Class 6 licence: $30 • Class 4 licence: $35 • Air Brake: $30**
*Cost may change ** There is no additional charge for the air brake test if you are taking a road test for a class
1, 2, 3, 4 or 5 licence and the vehicle you are using for the test is equipped with air brakes
• No cost applies for tests in these two situations: • You’re 65 or older; or • Our Medical Compliance and Assessments department requires you
to take the test
General Testing Information • There is a 30 minute time limit to complete a knowledge test
• Both knowledge and road tests are conducted during weekdays only (with the exception of holidays) at most locations. Saturday appointments are available at some Winnipeg locations
• Only one knowledge or road test of the same class may be completed per day
• There is a waiting period between the knowledge and road test for some classes of licences
• If you are in Graduated Driver Licensing and are not successful on your knowledge test, there is a seven day waiting period before you may take the test again
• If you are in Graduated Driver Licensing and are not successful on your road test, there is a 14 day waiting period before you may take the test again
• The knowledge test is not an open book test. Cellular phones and electronic devices are not allowed in the test area
• Please check-in 15 minutes prior to your scheduled appointment time
If you need to call one of these locations other than to book a test appointment:• In Winnipeg call 204–985–7000• Outside Winnipeg call 1–800–665–2410
Air Brake Manual • 5
BrakesandBraking
Section1
6 • Air Brake Manual
Heat–Energy–Traction–FrictionForavehicletomovealongthehighway,aninternalcombustionenginemustconvertitsheatenergyintomechanicalenergy.Thismechanicalenergygoesfromtheenginetothedrivingwheeltiresbymeansofasystemofconnectingrods,shaftsandgears.Thefinalfactorthatmovesthevehicleistheamountoftractionitstireshaveontheroadsurface.
Frictionistheforcethatresistsmovementbetweentwosurfacesincontactwitheachother.Tostopavehicle,thebrakeshoeliningsareforcedagainstthemachinedsurfacesofthebrakedrums,creatingfriction.Thisfrictionproducesheat.
Theengineconvertstheenergyofheatintotheenergyofmotion;thebrakesmustconvertthisenergyofmotionbackintotheenergyofheat.Thefrictionbetweenbrakedrumsandliningsgeneratesheatwhilereducingthemechanicalenergyoftherevolvingbrakedrumsandwheels.Theheatproducedisabsorbedbythemetalbrakedrums,whichdissipatetheheatintotheatmosphere.Theamountofheatthebrakedrumscanabsorbdependsonthethicknessofthemetal.Whenenoughfrictioniscreatedbetweenthebrakeliningandthedrums,thewheelsstopturning.Thefinalfactorthatstopsthevehicleisthetractionbetweenthetiresandtheroadsurface.
Ifa200–horsepowerengineacceleratesavehicleto100km/hinoneminute,imaginethepowerneededtostopthissamevehicle.Also,considerthatthevehiclemighthavetostopinanemergencyinaslittleassixseconds(just1/!)thetimeittooktoreach100km/h).
Tostopthevehiclein1/!)thetimeittooktoacceleratewouldrequireastoppingforceof10timestheaccelerationforce—theequivalentofapproximately2,000horsepower.Ifthevehiclehadsixwheels,eachwheelwouldhavetoprovide1/^thebrakingforce.Ifoneortwoofthewheelshadbrakesthatwerenotproperlyadjusted,theotherwheelswouldhavetodomorethantheirshareofthebraking,andthatmightbemorethantheirbrakeswereconstructedtostand.Excessiveuseofthebrakeswouldthenresultinabuildupofheatgreaterthanthebrakedrumscouldabsorbanddissipate.Toomuchheatresultsinbrakedamageandpossiblefailure.
Mostbrakeliningsoperatebestataround250°Candshouldnotexceed425°C.It’simportanttounderstandthatthepowerneededtostopgeneratesheatwhichcoulddamagethebrakes.
100 km/h
10X
Brake Drums
250°C Normal
1100°C Panic!
425°C Maximum
Air Brake Manual • 7
Speed–Weight–DistanceThedistancerequiredtostopavehicledependsonitsspeedandweight,inadditiontoenergy,heatandfriction.Thebrakingforcerequiredtostopavehiclevariesdirectlywithitsweightandspeed.Forexample,iftheweightisdoubled,thebrakingforcemustbedoubledtobeabletostopinthesamedistance.Ifthespeedisdoubled,thebrakingforcemustbeincreasedfourtimestobeabletostopinthesamedistance.Whenweightandspeedarebothdoubled,thebrakingforcemustbeincreasedeighttimestobeabletostopinthesamedistance.
Forexample,avehiclecarryingaloadof14,000kgat16km/hisbroughttoastopin30metreswithnormalapplicationofthebrakes.Ifthissamevehiclecarried28,000kgat32km/h,itwouldrequireeighttimesthebrakingforcetostopthevehiclein30metres.Thiswouldbemorebrakingforcethanthebrakescouldprovide.Novehiclehasenoughbrakingforcewhenitexceedsitslimitations.
Braking Force
Mechanical
Brakingsystemsusedevicestogainamechanicaladvantage.Themostcommondeviceforthispurposeisleverage.Aleverisplacedonapivotcalledthefulcrum.AsthedistancefromAtoCisfourfeet,andfromCtoBisonefoot,theratioisfourtoone(4:1).Forcehasbeenmultipliedbytheleverageprinciple.
Lookatthissimpleleversystem:
Ifa100lbdownwardforceisappliedatpointA,thentheupwardforceatpointBis400lb.
B = 400 lb
C
A = 100 lb
C
A 100 lb
S–cam brake
B 400 lb
B 400 lb
A B
4 feet 1 foot
C
Applied force = 100 lb
Delivered force = 400 lb
A
BC
8 • Air Brake Manual
Use of Air PressureForcecanalsobemultipliedbytheuseofairtogainfurthermechanicaladvantage.Everyonehasfelttheforceofaironawindyday.Aircanbecompressed(squeezed)intoamuchsmallerspacethanitnormallywouldoccupy,forinstance,aircompressedintirestosupporttheweightofavehicle.Thesmallerthespaceintowhichairissqueezed,thegreatertheair’sresistancetobeingsqueezed.Thisresistancecreatespressure,whichisusedtogainmechanicaladvantage.
Ifaconstantsupplyofcompressedairisdirectedthroughapipethatisoneinchsquare,andifaoneinchsquareplugwereplacedinthepipe,thecompressedairwouldpushagainsttheplug.Ascalecanbeusedtomeasurehowmanypoundsofforcearebeingexertedbytheairagainsttheplug.
Ifthescaleregisters10pounds,forexample,thenitcouldbesaidtheforceis10poundsontheonesquareinchsurfaceoftheplugor10poundspersquareinch(psi).
Themorecompressedtheairinthesupplyreservoir,thegreatertheforceexertedonthefaceoftheplug.
Leverage and Air PressureInactualoperation,pipesareroundandplugsarediaphragmsofflexiblematerialactingagainstpushrods.Ifcompressedairof120psiactsonadiaphragmof30squareinches,3,600lbofforceisproduced(120x30).Applythisforcetoapushrodtomovea6–inchslackadjusteroperatingacamandthetotalforceequals21,600inchpoundstorque(3,600x6),or1,800footpoundstorque(21,600÷12).Itrequires25to30footpoundsoftorquetotightenthewheelonacar.Thiscomparisonillustratestheforceobtainedfromusingmechanicalleverageandairpressurecombined.
Stopping DistanceStoppingdistanceconsistsofthreefactors:
•driver’sreactiontime
•brakelag
•brakingdistance
Driver’sreactiontime:Reactiontimeisoftencalled“thinkingtime”.Thetimeittakesfromthemomentahazardisrecognizedtothetimethebrakeisapplied,approximatelyPofasecond.
Brakelag:Asairishighlycompressible,itrequiresarelativelylargevolumeofairtobetransmittedfromthereservoirtothebrakechamberbeforethereisenoughpressureforthebrakestoapply.Itcanbesaidthatbrakelagisthetimeittakestheairtotravelthroughaproperlymaintainedairbrakesystem(approximately4/!)ofasecond).
1 square inch
10 psi
30 square inches
120 psi
6 inches
1 inch
Air Brake Manual • 9
Passenger car
Brakes applied
Loaded truck
Actual stop
Actual stop
Brakingdistance:Theactualdistancethevehicletravelsafterthebrakeisapplieduntilthevehiclestops.
Thedistancedependsontheabilityofthebrakeliningtoproducefriction,thebrakedrumstodissipateheatandthetirestogriptheroad.
Driversshouldnevertaketheirbrakesforgranted.Thebrakingsystemmustbetestedandtheadjustmentcheckedbeforeplacingthevehicleintoservice.Driversmustunderstandthebrakingsystem,realizeitscapabilitiesandlimitations,andlearntousethemtothebestadvantage.
Heavyvehiclesrequirepowerfulbrakingsystemsthatareobtainedbyuseofmechanicalleverageandairpressure.Brakesmustbeusedkeepinginmindtheheatgeneratedbyfriction.Iftheheatbecomestoogreat,brakingeffectivenesswillbelost.Theheaviertheloadandthefasterthespeed,thegreatertheforceneededtostop.
Itisimportanttorememberthatanairbrakeequippedvehicle,evenwithproperlyadjustedbrakes,willnotstopasquicklyasapassengercar.
Comparative Stopping Distances
Section Summary Questions
1. Whatisthefinalfactorthatwilldetermineifthevehiclewillmove?
2. Whatisthefinalfactorthatwilldetermineifthevehiclewillstop?
3. Howistheheatthatisgeneratedbythebrakesdissipated?
4. Ifonesetofbrakeshoesispoorlyadjusted,whateffectcouldithaveontheremainingsetsofbrakeshoesinthesystem?
5. Whatismeantbytheterm“friction”?
6. Iftheweightofthevehicleisdoubled,howmanytimesmustthestoppingpowerbeincreased?
7. Ifthespeedofthevehicleisdoubled,howmanytimesmustthestoppingpowerbeincreasedtobeabletostopatthesamedistance?
8. Ifbothweightandspeedofthevehiclearedoubled,howmanytimesmustthestoppingpowerbeincreasedtostopatthesamedistance?
9. Whatiscompressedair?
10. Whatdoestheabbreviation“psi”standfor?
11.If40psiisexertedagainstadiaphragmof30squareinchesinarea,whatarethetotalpoundsofforcethatcouldbeexerted?
12.Stoppingdistanceconsistsofwhatthreefactors?
13.Definethefollowingterms?
•Driver’sReactionTime
•BrakingDistance
•BrakeLag
10 • Air Brake Manual
Notes
Air Brake Manual • 11
TheComponentsofanAirBrakeSystem
Section 2
12 • Air Brake Manual
SectionOneofthismanualhasexplainedthatitispossibletogainamechanicaladvantagethroughtheuseofleversandthatairunderpressurecanbeusedtogainamechanicaladvantage.SectionTwowillexplainhowairunderpressurecanbeusedtooperatetheairbrakesofavehicle.
Pipingillustrationshavebeenkeptsimpleinordertobeeasilyunderstood.Thepipingarrangementsfoundonvehiclesinactualuseonthehighwaymightdiffersomewhatfromtheillustrationsinthismanual.
The Components of an Air Brake System
Abasicairbrakesystemcapableofstoppingavehiclehasfivemaincomponents:
1.Acompressortopumpairwithagovernortocontrolit.
2.Areservoirortanktostorethecompressedair.
3.Afootvalvetoregulatetheflowofcompressedairfromthereservoirwhenitisneededforbraking.
4.Brakechambersandslackadjusterstotransfertheforceexertedbythecompressedairtomechanicallinkages.
5.Brakeliningsanddrumsorrotorstocreatethefrictionrequiredtostopthewheels.
Itisnecessarytounderstandhoweachofthesecomponentsworkbeforestudyingtheirfunctionsintheairbrakesystem.
Compressor and Governor
Compressedairisusedtotransmitforceinanairbrakesystem.Thesourceofthecompressedairisacompressor(1).Acompressorisdesignedtopumpairintoareservoirwhichresultsinpressurizedair.
Thecompressorisdrivenbythevehicle’sengine,eitherbybeltsandpulleysorshaftsandgears.Invehicleswherethecompressorisdrivenbybelts,theyshouldbecheckedregularlyforcracksandtension.Also,checkthecompressorforbrokenmountingbracketsorloosebolts.
Thecompressorisinconstantdrivewiththeengine.Whenevertheengineisrunning,soisthecompressor.Whenpressureinthesystemisadequate,anywherefromalowof80psitoahighof135psiitisnotnecessaryforthecompressortopumpair.Agovernor(2)controlstheminimumandmaximumairpressureinthesystembycontrollingwhenthecompressorpumpsair.Thisisknownasthe“loading”or“unloading”stage.Mostcompressorshavetwocylinderssimilartoanengine’scylinders.Whenthesystempressurereachesitsmaximum,whichisbetween115and135psi,thegovernorplacesthecompressorinthe“unloading”stage.
Thecompressormustbeabletobuildreservoirairpressurefrom50to90psiwithinthreeminutes.Ifunabletodosothecompressorrequiresservicing.Acompressormaynotbeabletobuildairpressurefrom50to90psiwithinthreeminutesiftheairfilterispluggedorifthebeltwasslipping,ifthesewerenotatfaultthecompressorcouldbefaulty.
Governor
Pressure setting spring
Exhaust port
Unload port
Reservoir port
Exhaust port
Unload port
Reservoir port
Air Brake Manual • 13
Placingthecompressorintheunloadingstageisdonebydirectingairpressuretotheinletvalvesofthecompressor,holdingthemopen,allowingtheairtobepumpedbackandforthbetweenthetwocylinders,insteadofcompressingtheair.Whenthepressureinthesystemdrops,theinletvalvesclose,returningthecompressortothe“loading”stage.Thegovernormustplacethecompressorinthe“loading”stageatnolowerthan80psi.Duringthe“unloading”stage,thecompressorisabletocool.
Usuallycompressorsarelubricatedfromtheenginelubricationsystem,althoughsomecompressorsareself–lubricatingandrequireregularchecksofthelubricantlevel.
Itisveryimportanttheairthatentersthesystembekeptascleanaspossible.Theairmustfirstpassthroughafiltertoremoveanydustparticles.Theairfiltermustbecleanedregularly.Adirtyfilterwillrestricttheflowofairintothecompressor,reducingitsefficiency.Somevehicleshavetheinletportofthecompressorconnectedtotheintakemanifoldandreceiveairthathasbeenfilteredbytheengineaircleaner.
Apistontypecompressoroperatesonthesameprincipleastheintakeandcompressionstrokesofanengine.
• Intakestroke:Thedownwardstrokeofthepistoncreatesavacuumwithinthecylinderwhichcausestheinletvalvetoopen.Thiscausesatmosphericairtoflowpasttheinletvalveintothecylinder.
Piston
From governor
Intake air filter
Unload plunger
Inlet valve
Discharge valve
Compressor (Unloading stage)
Intake air filter
Unload plunger
Inlet valve
Discharge valve
Compressor (Intake stroke)
Piston
14 • Air Brake Manual
•Compressionstroke:Theupwardmotionofthepistoncompressestheairinthecylinder.Therisingpressurecannotescapepasttheinletvalve(whichthecompressedairhasclosed).Asthepistonnearsthetopofthestroke,thepressurizedairisforcedpastthedischargevalveandintothedischargelineleadingtothereservoir.
Reservoirs
Reservoirsortanksholdasupplyofcompressedair.Thenumberandsizeofthereservoirsonavehiclewilldependonthenumberofbrakechambersandtheirsize,alongwiththeparkingbrakeconfiguration.Airbrakevehiclesareequippedwithmorethanonereservoir.Thisgivesthesystemalargervolumeofmainreservoirair.Thefirstreservoirafterthecompressorisreferredtoasthesupplyorwet(5)reservoir.Theotherreservoirsareknownasprimary(8)andsecondary(10)ordry(8)(10)reservoirs.Whenairiscompressed,itbecomeshot.Theheatedaircoolsinthereservoir,formingcondensation.Itisinthisreservoirthatmostofthewateriscondensedfromtheincomingair.Ifoilleakspastthepistonringsofthecompressorandmixeswiththismoisture,itformssludge,which
accumulatesinthebottomofthereservoir.Ifallowedtoaccumulate,thissludge(waterandoil)wouldenterthebrakingsystemandcouldcausetroublewithvalvesandotherparts.Inwinter,waterinthesystemmayfreeze,causingthemalfunctionofvalvesorbrakechambers.Reservoirsareequippedwithdrainvalvessothatanymoistureorsludgethatmayhaveaccumulatedcanbedrained.Ifyounoticesludgewhendrainingyoursystem,haveitinspectedbyamechanic.Tominimizetheamountofwatercollection,allreservoirsmustbedraineddaily.Underextremeconditions,reservoirsmayhavetobedrainedmorethanonceaday.Todrainthereservoirsalwaysstartwiththewetreservoironthetractor.Openthedrainvalvefullyandallowallairpressuretoescape,whichwillalsoexhaustthemoisturecollectedinthereservoir.
Somereservoirshavemorethanonecompartmentandeachcompartmenthasitsowndrainvalve,whichmustbedrainedindividually.Brieflyopeningthevalvejusttoallowsomeoftheairtoescapedoesnotdrainthemoisture!Itisnotsafetoassumethatthewetreservoir,orthepresenceofanairdryerisreasontoneglecttheotherreservoirsonthepowerunit,trailersordollies.Theyshouldallbecompletelydraineddailybyopeningthedrainvalvefullyandallowingalloftheairtoescape.Thisshouldbedoneduringthepost–tripinspectionattheendoftheday.Seepost–tripInspectionlaterinthismanualformoreinformation.
Somereservoirsmaybeequippedwithautomaticreservoirdrainvalves(spittervalves).Thesevalveswillautomaticallyexhaustmoisturefromthereservoirwhenrequired,althoughtheyshouldbecheckeddailyanddrainedperiodicallytoensurethemechanismisfunctioningproperly.Anylooseordisconnectedwiresassociatedwiththevalveheatersshouldberepairedimmediately.
Reservoir
Intake air filter
Unload plunger
To reservoir
Inlet valve
Discharge valve
Compressor (Compression stroke)
Piston
Air Brake Manual • 15
Air Dryer
Anairdryer(3)maybeinstalledbetweenthecompressorandthewetreservoirtohelpremovemoisturefromthecompressedair.Itmaybepartiallyfilledwithahighmoisture–absorbentdesiccantandanoilfilter,oritmaybehollowwithbafflesdesignedtoassistinseparatingthemoisturefromtheair.Bothtypesofairdryersuseairpressuretopurgeorejecttheaccumulatedcontaminantsfromtheirdesiccantbed.Thepurgevalvehasaheaterelement,whichpreventsthemoisturefromfreezingincoldclimateoperation.Thewiringconnectedtotheheatershouldbeinspectedforlooseordisconnectedwires.Theyarealsoequippedwithasafetyvalve.
Control port
Supply port
Cut–off piston
Exhaust
Purge valve
Delivery port
One–way check valve
One–way check valveOrifice
Desiccant bed
Control PortDried Air
Check valve assembly
Delivery Port
Heater element
ExhaustPurge valve
Cut–off piston
Supply Port
ReservoirCompressor
GovernorSump
Air Dryer (Purge cycle)
Desiccant Cartridge
Air Dryer (Drying cycle)
Air Dryer
Control Port
Supply Port
Oil Separator
16 • Air Brake Manual
Safety Valve
Asafetyvalve(4)protectsreservoirsfrombecomingoverpressurizedandburstingifthegovernormalfunctionedanddidnotplacethecompressorintheunloadingstage.Thevalveconsistsofaspring–loadedballthatwillallowairtoexhaustfromthereservoirintotheatmosphere.Thevalve’spressuresettingisdeterminedbytheforceofthespring.Asafetyvalveisnormallysetat150psi.Ifthepressureinthesystemrisestoapproximately150psi,thepressurewouldforcetheballoffitsseat,allowingthepressuretoexhaustthroughtheexhaustportinthespringcage.Whenreservoirpressureissufficientlyreducedtoapproximately135psi,thespringwillforcetheballbackontoitsseat,sealingoffthereservoirpressure.Notallsafetyvalveshaveamanualreleasefeature.
Ifthesafetyvalvehastorelievepressure,thegovernororcompressorrequiresadjustment,serviceorrepair.Thisshouldbedonebyaqualifiedmechanic.
Foot Valve
Thefoot–operatedvalve(31)isthemeansofapplyingairtooperatethebrakes.Thedistancethetreadleofthefootvalveisdepressedbythedriverdeterminestheairpressurethatwillbeapplied,butthemaximumapplicationwillnotexceedthepressureinthereservoir.Releasingthefootvalvetreadlereleasesthebrakes.
Whenthedriverappliesthebrakes,depressingthetreadlepartway,thefootvalvewillautomaticallymaintaintheapplicationairpressurewithoutthedriverhavingtoadjustthepressureofhisfootonthetreadle.
Releasingthetreadleallowstheapplicationairtobereleasedthroughtheexhaustportsintotheatmosphere.Airtreadlesarespringloaded,producingadifferent“feel”fromhydraulicbrakeapplications.
Brake Chambers, Slack Adjusters and Brake Lining
Brake Chamber and Slack Adjuster (Brakes off)
Treadle
Treadle spring
Supply from reservoir
Exhaust Port
Push rod
Brake chamber
DiaphragmDiaphragm
return spring
Air inlet
Mounting bolts
Clevis and pin
Slack adjuster
Air pressure greater than 150 psi
Safety Valve
Foot Valve
To brake chambers
Air Brake Manual • 17
Abrakechamber(11)(14)(32)isacircularcontainerdividedinthemiddlebyaflexiblediaphragm.Airpressurepushingagainstthediaphragmcausesittomoveawayfromthepressure,forcingthepushrodoutwardagainsttheslackadjuster.Theforceexertedbythismotiondependsonairpressureanddiaphragmsize.Ifaleakoccursinthediaphragm,airisallowedtoescape,reducingtheeffectivenessofthebrakechamber.Ifthediaphragmiscompletelyruptured,brakesbecomeineffective.
Frontbrakechambers(32)areusuallysmallerthanthoseintherearbecausefrontaxlescarrylessweight.Abrakechamberisusuallymountedontheaxle,nearthewheelthatistobeequippedforbraking.Airpressureisfedthroughaninletport.Theairpushesagainstthediaphragmandthepushrod.Thepushrodisconnectedbyaclevisandpintoacrankarm–typelevercalleda“slackadjuster”.ThisconvertsthepushingmotionofthepushrodfromthebrakechambertoatwistingmotionofthebrakecamshaftandS–cams.Whentheairisexhausted,thereturnspringinthebrakechamberreturnsthediaphragmandpushrodtothereleasedposition.
Asindicatedbyitsname,theslackadjusteradjuststhe“slack”orfreeplayinthelinkagebetweenthepushrodandthebrakeshoes.Thisslackoccursasthebrakeliningswear.Iftheslackadjustersarenotadjustedwithinthelimitations,effectivebrakingisreducedandbrakelagtimeisincreased.Iftoomuchslackdevelops,thediaphragmwilleventually“bottom”inthebrakechamber,andthebrakeswillnotbeeffective.
Illustratedbelowaretwocommontypesofmanualslackadjusters,showingthewormadjustinggear.
Push rod
Brake chamber
Diaphragm Diaphragm return spring
Air inlet
Mounting bolts
Clevis and pin
Slack adjuster
Manual Slack Adjusters
Ball Indent Slack Adjuster Positive Lock Slack Adjuster
Lock screw
Adjusting bolt Worm shaft
Worm gear
Locking collar
Spline Spline
Grease fitting
Adjusting bolt
Brake Chamber and Slack Adjuster (Brakes on)
18 • Air Brake Manual
Onmanualslackadjusters,theadjustingwormboltisturneduntilthebrakeliningstouchthedrumsandthenbackedoff,normallyN toMaturn.Alockingdevice,whichmaybeaspringloadedcollarovertheheadoftheadjustingbolt,mustbedepressedwhenthewrenchisslippedoverthebolthead.Thisisknownasapositivelockslackadjuster.
Ortheycoulduseaspring–loadedinternalcheckballtolocktheadjustment,anditmustberemovedtomakeanyadjustment.Thisisknownasaballindentslackadjuster.Themoreoftenthedriverchecksthe“slack”,thelesstheprobabilityofbrakefailure.Vehiclesrarely“lose”theirbrakesbecauseofairloss;itisusuallybecausetheyareoutofadjustment.
Itisthedriver’sresponsibilitytoensurethatbrakesareadjustedcorrectly.Asimpleservicebrakeapplicationatlowspeedtocheckbrakeadjustmentisnotadequate.Brakingathighwayspeedcausesbrakedrumexpansionduetoheat,whichinturnrequiresgreaterpushrodtraveltomaintainthesamebrakingforce.Ifabrakeisoutofadjustmenttherewouldnotbeenoughreservestrokeofthepushrodtraveltocompensatefordrumexpansion.Thiswouldcauseabrakefadeandwouldgreatlyextendstoppingdistance.Iftravellingdownahill,thiscouldcausecompletebrakeloss.
Note:DetailedbrakeadjustmentproceduresareoutlinedinSection8.
Pushrod
Air inlet
Slack adjuster
Brake Chamber and Slack Adjuster (Brakes on)
Thrust washer
Clevis
Clevis pin (large)Clevis pin (small)
Actuator rod
Hairpin clip
Boot and strapActuator (adjusting sleeve)
Roller (pin)
Actuator piston
Pressure relief capscrew (pull pawl)
Pawl spring
Adjusting pawl
Worm
Worm seal
Adjusting bolt
Grease groove
Grease fitting
Housing
Worm gear
Automatic Slack Adjuster
Air Brake Manual • 19
Somesystemshaveautomaticslackadjustersthatadjustautomaticallytocompensateforbrakeliningwear,usuallymaintainingthecorrectclearancebetweenthebrakelininganddrum.Automaticslackadjustersmustbecheckedregularlytoensurethatcorrectadjustmentisbeingmaintained.Therearevariousmakesandmodelsofautomaticslackadjustersinuse.Primarily,theyareeitherstroke–sensingorclearance–sensing.Astroke–sensingadjusterwilladjusttheslackwhenitsensesthesetstrokeisexceeded.Aclearance–sensingadjusterwilladjustwhentheproperclearancebetweenthebrakedrumandbrakeshoeisnotmaintained.Someautomaticslackadjustershavetheabilitytoback–offorincreasetheslackwhenithasoveradjustedthebrake.Ifavehicleisequippedwithautomaticslackadjusters,itshouldnotbetakenforgrantedthatthebrakeswillalwaysbeinadjustment.Thesystemisnotfoolproof.Anumberoffactorscouldresultintheautomaticslackadjusternotmaintainingproperslack.Therecouldbeimproperinstallation,inadequatemaintenance,deformedbrackets,worncambushings,bentpushrods.Evenpoorvisualinspectioncanresultinproblemsunrelatedtoadjusterfunction.Whenconductingapre–triporpost–tripairbrakeinspection,lookforwornordamagedcomponents.Automaticslackadjusterscanmalfunctionandnotkeepthebrakeinadjustment,especiallywhenithasbeeninserviceforalongperiodoftime.Thetwomostcommonproblemsareexcessiveprematurewearandinternalcontamination.Asanautomaticslackadjusteragesinservice,thecomponentswearthatsensewhenanadjustmentisrequired.Theresultismorestrokeisrequiredfortheliningtocontactthebrakedrum,andifnotcheckedthebrakecouldbeoutofadjustment.Ifevenasmallamountofwaterissuckedintoanautomaticslackadjustermechanismitcancause
corrosionor,inwinter,itcanfreezetheinternalsensingcomponentsandinhibitorpreventadjustment.Also,undercertainconditions,anautomaticslackadjusterthatdoesnothavetheabilitytoback–offorincreaseslack,mayoveradjustabrakecausingittodrag.Forexamplethiscouldtakeplacewhenatractor–trailerisnegotiatingalong,curvingdowngrade.Thedrivershould“snub”thebrakes,whichisrepeatedlyapplyingthebrakesmoderatelytomaintainsafecontrolofthevehicle.Howeveritwouldnottakelonginthisseverebrakingconditionforoneormoreofthebrakedrumstooverheatandexpand.Theoverheatingwillphysicallyincreasethebrakedrumsdiameter,andinextremeandprolongedconditionswillleadtolongerpush–rodstrokestoachievethebrakingforcerequired.Theautomaticslackadjusterinterpretsthisasaneedforadjustmentandwilltakeupslack.Whenthebrakedrumcoolsdownandreturnstonormalsizethebrakesareoveradjustedanddragging.Atthattimethedrivershouldstopandcheckthebrakesforadjustment.Anumberoffullbrakeapplicationsabove90psiperdayarerequiredtokeeptheautomaticslackadjustersinadjustment(seeSection8formoreinformation).
Becauseautomaticslackadjustersarenotfoolproof,itisimportanttheoperatorofavehicleequippedwithautomaticslackadjustersbeabletomanuallyadjustthem.Forinformationonmanuallyadjustingtheautomaticslackadjustersonyourvehicleconsultthemanufacturer.
Illustratedisacommontypeofbrakeassemblyusedontruckrearaxlesandtraileraxles.Afrontaxleassemblyhasthebrakechamberandslackadjustermountedonthebacking–platebecauseofthesteeringaction.
Brake drum
Brake chamberPush rod, clevis and pin
Slack adjuster
S–cam
Brake lining
Brake Assembly
20 • Air Brake Manual
Brakeliningmaterialisattachedtotheshoes.Thematerialuseddependsonthebrakingrequirementsofthevehicle.Brakeliningmustgiveuniformoutputofbrakeeffortwithminimumfadeathightemperatures.
Fadingorreductioninbrakingeffortoccurswhentheheateddrumsexpandawayfromthebrakelinings.Thebrakeliningsalsolosetheireffectivenesswithoverheating.
ThetwistingactionofthebrakecamshaftandS–camforcesthebrakeshoesandliningsagainstthedrums.Thebrakeliningsgenerateheatfromfrictionwiththebrakedrumsurface.
Thethicknessofthedrumsdeterminestheamountofheattheyareabletoabsorbanddissipateintotheatmosphere.Drumswornthinwillbuildupheattooquickly.Dangerouslyundependablebrakeperformancewillresultfromdistorteddrums,weakreturnsprings,improperlining,pooradjustment,orgreaseordirtonthelining.Drumsmustneverbemachinedorwornbeyondthemanufacturer’sspecification.
Wedge Brakes
Thisisanotherexampleofabrakeassemblyusedonsomeairbrake–equippedvehicles.Theactionofthebrakechamberpushrodforcesawedge–shapedpushrodbetweenthebrakeshoerollers.Thisforcesthebrakeshoeliningagainstthebrakedrum.
Thevehiclemaybeequippedwithasingleordualchambersoneachwheel,dependingonthevehicle’ssizeandstyle.
Thesebrakesmaybeequippedwithaself–adjustingmechanismorwithamanual“starwheel”adjuster.Thestarwheeladjustmentismadewiththevehiclejackedup,toinsurethatthebrakeliningsdonotdrag.Manualadjustmentofwedgebrakesisusuallydonebyaqualifiedmechanic.
Brake chamber
Adjusting wheel
Brake shoe roller
Push rod
Shoe return spring
Brake lining
Brake shoe
Wedge Brake – Single Chamber
Brake chamber
Single chamber Dual chamber
Shoe return springs
Brake lining
Adjusting wheel
Brake chambers
Adjusting wheel
Wedge Brakes
Air Brake Manual • 21
Disc Brakes
Theair–activatedheavytruckdiscbrakeissimilarinprincipletothatusedonpassengervehicles.Airpressureactsonabrakechamberandslackadjuster,activatingthebrakes.Insteadofthecamorwedgeusedinconventionalheavytruckdrumbrakes,a“powerscrew”isused.ApowerscrewworkslikeaC–clamp,sothattheliningpadsexertequalforcetobothsidesofthediscorrotor.Sometypesofdiscbrakeshaveabuilt–inautomaticadjuster.DiscbrakesthatrequiremanualadjustmenthaveadjustmentspecificationsthatdifferfromconventionalS–cambrakingsystems.Alwayscheckthemanufacturer’sspecificationsbeforeadjusting.Discbrakeassembliesmayhaveaspringparkingbrakeunitattachedtotheservicebrakechamber.
Air–Over–Hydraulic Brake Systems
Air–over–hydraulicbrakesystemsweredevelopedformediumweightvehiclesbecause:
• dieselenginesdonothaveasourceforvacuumboostingunlesstheyareequippedwithavacuumpump.
• mediumweightvehiclesdonotrequireafullairbrakesystem.
• itgivestheoptionofpullinganairbrakeequippedtrailer.
Thesesystemscombinethebestfeaturesofanairandhydraulicbrakesystem.Theyusehydraulicbrakesateachwheelwiththeirreliableselfadjustersandlimitedmaintenance.Onthesesystemstheairisusedtoeitheractuatethehydraulicbrakesorboostthehydraulicbrakepressureasexplainedinthefollowing.
Air–Actuated Hydraulic Brake System (Air Brake Endorsement Required)
Anair–actuatedsystemusuallyhasthesamecomponentsofastandardairsupplysystemincludingawarningbuzzerandlight,compressor,governor,wetanddryreservoirs,andafootvalvethatcouldbeasingleordualtype.Thesecomponentsarefoundusuallyinthesameplacesasonafullairbrakesystem.Alsothereareoneortwoairactuatedhydraulicpressureconvertersdependingonifthesystemisasingleoradualsystem.Thissystemconsistsofanairchamberorcylinderattachedtoahydraulicmastercylinder.Whenthefootvalveisdepressed,theairpressureactuatesthepushrodfromtheairunitthatpushesagainstthemastercylinderpiston,producinghydraulicpressuredirectedthroughtubingtothewheelcylindersactuatingthefrontandrearaxleservicebrakes.
Disc Brake
22 • Air Brake Manual
Itisessentialthattheoperatorofsuchavehiclehaveknowledgeofairpressurebuilduptime,governorloadingandunloadingpressure,warningdeviceoperation,andhowtodrainairreservoirsproperly(seeSectionNine;Pre–TripAirBrakeInspection).
Ifanair–actuatedhydraulicbrakesystemwastoloseitsairsupply,thevehiclewouldhavenoservicebrakes.Onlytheparkingbrakewouldbeoperatingasitismechanicalandrequiresnoairpressuretooperate.
Eachvehiclemanufacturermayhavedifferentparkingbrakeapplications,eitherautomaticallywhenairpressureisreducedinthereservoir,ormechanicallybyabrakeontherearofthetransmission,orwiththerearbrakesystem.Sincehydraulicbrakesystemsactuatedbyairpressureareregardedasanairbrakesystem,yourdriver’slicencemusthaveanairbrakeendorsementforyoutooperatevehiclesequippedwithair–activatedhydraulicbrakes.
Astherearemanydifferentsystemsinuse,refertotheoperator’smanual.
Air–Boost Hydraulic Brake System (Air Brake Endorsement not Required)
Anair–boosthydraulicbrakesystemusesairpressuretoassistbrakeforce.Thisissimilartovacuum–assistedbrakesonmostpassengervehicles.Anair–boostsystemusuallyhasthesamecomponentsofastandardairsupplysystemincludingacompressor,governor,wetanddryreservoirs.Thesecomponentsarefoundusuallyinthesameplacesasonafullairbrakesystem.Thebrakepedallinkageoperatesahydraulicmastercylinderthatsendshydraulicpressuretotheboosterunit.Initially,atlowpressurethehydraulicfluidpassesthroughtheboosterandbeginstopressurizethewheelcylindersmovingthebrakeshoesouttothedrums.Theseboosterunitsaresimilarinoperationto“Hypower”or“Hydrovac”vacuumboostersfoundonmostlightandmediumweightvehicles,butairpressureisusedtointensifythehydraulicpressuregeneratedbythemastercylinderratherthanvacuum.Builtintotheboosterunitisahydraulicallyoperatedaircontrolvalve.
Air linesReservoirsCompressor
Foot valve
Hydraulic lines
Air brake chamber
Hydraulic wheel
cylinders
Hydraulic wheel
cylinders
Air lines
Air brake chamber
Hydraulic master cylinder
Hydraulic master cylinder
Air–Actuated Hydraulic Brake System
Air Brake Manual • 23
Thisiswhereairfromthereservoirisdirected.Asthepressurefromthemastercylinderincreases,theaircontrolsectionintheboosterwillopenandbegintodeliverairpressuretotherearoftheaircylinder.Theaircylinderpushrodtransferspressureonapistoninthehydraulicsectionofthebooster,increasingthehydraulicpressureatthewheelcylinders.
Thedriverhasfullcontrolofthebrakingforceastheaircontrolsectionmodulatestheboostpressureinproportiontothemastercylinderpressure.Ifthevehiclewastolosealloftheairpressurethebrakesystemwouldlosetheairassistboost,howeverthehydraulicsystemwouldcontinuetoworkbutatreducedeffectiveness.Anairbrakeendorsementonadriver’slicenceisnotrequiredtooperateavehiclewiththisbrakesystem.Consulttheoperator’smanualforthevehicleyoudriveformaintenancerequirements.
Air lines
Hydraulic wheel
cylinders
Compressor
Reservoir Hydraulic master cylinder
Brake pedal
Hydraulic lineBooster unit
Air–Boost Hydraulic Brake System
Air lines Booster unit
Hydraulic line
Hydraulic wheel
cylinders
24 • Air Brake Manual
Section Summary Questions
1. Whatarethefivebasiccomponentsofanairbrakesystem?
2. Atwhatpressureshouldthegovernorcausethecompressortoreturntoits“loading”stage?
3. Atwhatpressurewillthegovernorplacethecompressorinthe“unloading”stage?
4. Howisapluggedairfilterlikelytoaffecttheaircompressor?
5. Whatcausesmoisturetoformintheairbrakesystem?
6. Whenisthecompressorabletoaccomplishmostofitscooling?
7. Howaremostcompressorslubricated?
8. Howoftenshouldthereservoirsbedrained?
9. Isitnecessarytoallowallthepressuretoescapefromthereservoirinordertoremovethemoistureandsludgewhichmayhaveaccumulated?
10. Whatisthemaximumpressureavailableforafullbrakeapplicationatanygiventime?
11. Whatwillresultifthebrakedrumsarewornthinorturnedtoofar?
12. Ifthegovernorvalvefailedto“unload”thecompressor,whatwouldprotectthereservoirsfrombecomingoverpressurizedandbursting?
13. Whatisthepurposeofhavingmorethanonereservoir?
14. Whataretwofunctionsoftheslackadjusters?
15. Doestheamountofslackinthebrakelinkageshaveanyeffectonthebrakingefficiencyofthevehicle?
16. Whatistheadvantageofkeepingthebrakechamberpushrodtraveladjustedwithinlimitations?
17. Whatisthemostcommoncauseoflossofeffectivebrakinginanairbrakesystem?
18. DoautomaticslackadjustersonS–cambrakesrequirechecking?
19. Cantheadjustmentonair–operateddiscbrakesdifferfromS–cambrakes?
20. Whatoccurswhendrumbrakesbecomeoverheated?
21. Whatcausesbrakefade?
22. Whatisthemainfunctionofthefootvalve?
23. Whydoesthe“feel”ofanair–operatedfootvalvedifferfromahydraulicbrakepedal?
24. Onwhatprincipledoesadiscbrakeoperate?
25. Whattypeofair–over–hydraulicbrakesystemrequirestheoperatortoholdanairbrakeendorsement?
Air Brake Manual • 25
HowtheBasicSystemWorks
Section3
26 • Air Brake Manual
Basic Air Brake System
Airispumpedbythecompressor(1)tothewetreservoir(5),whichisprotectedfromoverpressurizationbyasafetyvalve(4).Thegovernor(2)controlsthepressureinthereservoirtothebottomofthefootvalve(31).Thedriverpushesthefootvalvetreadledownandairpressureflowstothefrontandrearbrakechambers(32&11).Thebrakechamberpushrodsmovetheslackadjusters.TheslackadjustersrotatetheS–cams,forcingthebrakeshoesagainstthedrums.Thiscausesfrictionthatstopsthewheels.Thedriverreleasesthefootvalvetreadleandtheairinthebrakechambersisallowedtoexhaustthroughthefootvalve,releasingthebrakes.
Thefollowingexplainstheadditionalcomponentsofabasicairbrakesystem.Othervalveswhicharenecessarytoensuresmoothandefficientoperationsarenotincludedinthissimpledrawing.Theywillbediscussedlaterinthemanual.
Note:Anairdryer(3)hasbeenaddedtoreducetheamountofmoistureinthesystem.
One–Way Check Valve
Inthediagrambelow,tworeservoirsareshown(5)(10).Topreventairfromflowingbackwardsinthesystemtowardthecompressor,aone–waycheckvalve(7)isinstalledbetweenthereservoirs.Thisvalveallowstheairtoflowinonedirectiononly.Thevalveisspringloaded.
Pressureattheinletsideovercomesthespringpressureandliftsthecheckvalveball,ordisc,offitsseat.Airpassesthroughthevalvetotheoutlet.Whenpressureattheoutletbecomesgreaterthanattheinlet—togetherwiththespringpressure—thecheckdeviceseats,preventingairfromflowingbackthroughthevalve.
123 4 5 7 9 1032 11
32 31 11
Basic Air Brake System
Ball
Spring
Body
Cap nut
One–Way Check Valve
Air Brake Manual • 27
Air Pressure Gauge
Vehicleswithanairbrakesystemareequippedwithareservoirairpressuregauge(29).Thisgaugeismountedinthecab,usuallyonthedashboardandindicatestheairpressureintheprimaryandsecondaryordryreservoirs.Thesupplyorwetreservoirdoesnotusuallyhaveanairpressuregauge.Commonoperatingpressuresare80to135psi,dependingonthesystem.Monitoringthegaugewillalertthedrivertoanyunusualchangesinairpressure.
Brake Application Gauge
Anadditionalgaugecanbeinstalledonthedashtoindicatetheapplicationairpressurewhenthebrakesareapplied.Thisgaugecanbepipedtoindicatethepressureofeitherafootorhandapplication.(Handapplicationwillbeexplainedlaterinthemanual.)
Low Pressure Warning Device
Allvehiclesequippedwithanairbrakesystemmusthaveadevicetowarnthedriveriftheairpressureinthesystemdropstoadangerouslevel.Thisdevicecouldbearedwarninglight,abuzzerorawig–wag.Duetooveruseorleaks,thelowpressureindicatorswitch(9)willturnonaredwarninglightonthedashorcauseabuzzertosoundatorbefore60psi.Somevehiclesareequippedwithbothalightandabuzzertowarnthedriverofalowairpressurecondition.
Wig–wagsarenotfoundinmodernvehicleshavingbeenreplacedwitharedwarninglightandbuzzer.Theymaystillbeinuseonoldervehicles.Therearetwotypesofwig–waglowpressurewarningdevicesthatmaybeused.Bothtypeswilldropintothedriver’sviewshouldthesystempressuredropto60psi.Theautomaticwarningdevicewillriseoutofthedriver’sviewwhenthepressureinthesystemrisesabove60psi.Themanualresettypemustbeplacedinthe“outofview”positionmanuallyandwillnotstayinplaceuntilthepressureinthesystemgoesabove60psi.
Whicheverwarningsystemisused,buzzer–lightsorwig–wag,thedrivermuststopthevehicleinasafeplaceimmediatelyandfindthecauseoftheairloss.Theairpressureremaininginthesystem(approximately60psi)isenoughforabrakeapplicationifthedriveractspromptly.
Keepinmindifthevehiclehasspringparkingbrakes,at60psithespringparkingbrakesarepartiallyappliedandyoucannotreleasethemuntilairpressureincreases.Ifyoudonotmoveyourvehicletoasafeplaceyoumayfindyourselfstrandedinthetraveledportionofthehighway.
Stop Light Switch
Anydriverfollowingyourvehiclemustbewarnedwhenreducingspeedorstoppingthevehicle.Thestoplightswitch(25)isanair–operatedelectricswitchthatturnsonthebrakelightsattherearofthevehiclewhenabrakeapplicationisbeingmade.
28 • Air Brake Manual
Quick Release Valve
Theapplicationofthebrakesinthebasicsystemwasdescribedearlier.Inabasicsystem,whenthedriverreleasesthefootvalve,itwouldbenecessaryfortheairunderpressureinthebrakechamberstoreturntothefootvalvetoreleasethebrakes.Thisreleasingactionwouldbeslowedinlongwheelbasevehiclesbecauseofthelongerlinesbetweenthefootvalveandtherearbrakechambers.Aquickreleasevalve(33)isinstalledtoallowthebrakestoreleasequicklyandfullybydischargingtheapplicationairnearthebrakechambers.Toallowthebrakestoreleasequicklyandfullybydischargingtheapplicationairnearthebrakechambers.
Relay Valve
Thefootvalveisusuallylocatedclosertothefrontwheelsthantotherearwheels.Thelongerthedistancefromthefootvalvetotherearchambers,themoretimeitwilltakebeforetherearbrakesapply.Thisisknownasbrakelag.Tocorrectthisconditiononalongwheelbasevehicle,arelayvalve(13)isinstalledneartherearbrakechambers.Alargerdiameterpipeisconnectedbetweenthemainreservoirandtherelayvalve.Theairlinefromthefootvalvetotherelayvalvenowbecomesa“controlline”.(Theairinthecontrolline“deadends”attherelayvalve.)Whenthefootvalveisdepressed,theairpressureinthecontrollineactsonthetopsectionoftherelayvalve,relayingreservoirairdirectlytotherearbrakechambersthroughthelargerdiameterpipe.Thepressureofthereservoirairdeliveredinthiswaywillbethesameasthecontrolpressuredeliveredbythefootvalve.
Releasingthefootvalveexhauststhecontrolairtotherelayvalve,allowingittocutofftheflowofreservoirairtotherearchambers.Thisinturnexhauststheairinthebrakechambersbythequickreleasefeatureoftherelayvalve.
Manual Front Brake Limiting Valve
Forbettersteeringcontrolwhenbrakingonaslipperyroadsurface,itcanbeanadvantagetoreducethebrakingefforttothefrontwheels.Thiscanbeaccomplishedbyinstallingacontrolvalve(35)inthecab,andafrontbrakelimitingvalve(36)onthefrontaxle.
Thecontrolvalveissetinthe“normal”positionfordryroadsurfacesandthefrontbrakingapplicationairpressureisnormal.Onaslipperyroadsurface,thecontrolvalve(35)issettothe“slipperyroad”position.Inthisposition,thecontrolvalvewillcausethelimitingvalve(36)tooperate.Applyingairpressuretothefrontbrakesisthenreducedto50percentoftheapplicationairpressurebeingdeliveredtotherearbrakechambers.
Delivery ports not shown
Manual Front Brake Limiting Valve
Dash Mounted Control Valve
Service port Lever
Exhaust port Service port
To limiting valve
From limiting
valve
Relay Valve
Quick Release Valve
Air Brake Manual • 29
Somesystemsareequippedwithanautomaticlimitingvalve(34).Thisvalvewillholdoffbrakeapplicationtothefrontwheelsfrom0to10psi,dependingonhowithasbeenpreset.Betweenthepresetpressureand40psiofbrakeapplication,thereductionis
approximately50percent.Brakeapplicationsbetween40psiand60psiarereducedbylessthan50percent.Brakeapplicationsmorethan60psiarenotreducedandfullapplicationisdirectedtothefrontwheels.
12
3 45
6 7 6 8 932 11
1135
31
32
29
1336
Service port Service port
Delivery port Delivery port
Piston spring
Inlet–exhaust valve springLower piston
assembly
Automatic Front Brake Limiting Valve
Basic Air Brake System with Manual Front Brake Limiting Valve
30 • Air Brake Manual
Theairbrakesystemdiscussedpreviouslyisforavehiclewithasinglerearaxle.Thediagramillustratesanairbrakesystemforavehicleequippedwithanautomaticfrontbrakelimitingvalve(34),aquickreleasevalve(33)andatandemsetofrearaxles.Bothaxlesofthetandemsetareequippedwithbrakes.
Arelayvalve(13)hastwouses:toprovideaquickerapplicationofairpressuretothetandemrearaxlebrakeswhenabrakeapplicationismade,andtoreleasethebrakesquickerwhenabrakeapplicationisreleased.
Section Summary Questions
1. Howcanthedrivertellhowmuchairpressureisinthemainreservoirs?
2. Whatmustthedriverdowhenalowpressurewarningsystemactivates?
3. Whatisthepurposeofaquickreleasevalve?
4. Whatisthepurposeofarelayvalve?
5. Whatisthepurposeofusingalargerdiameterpipebetweenthereservoirandtherelayvalve?
6. Ifthefrontbrakelimitingvalveisinthe“slipperyroad”position,andthefootvalveisdepressedtomakeabrakeapplicationof30psi,howmuchpressurewillbeappliedinthefrontbrakechambers?
7. Howisthereservoirprotectedfromoverpressurization?
8. Whatstopspressurizedairfromflowingfromthedryreservoirbackintothecompressor?
9. Atwhatpressureshouldthelowpressurewarningdeviceactivate?
10. Howis“brakelag”totherearwheelsminimized?
11. Whenshouldadriverusethefrontbrakelimitingvalve?
34
33 13
Tandem Rear Axles
Air Brake Manual • 31
SpringParkingBrakes
Section4
Spring Parking Brake Systems(Single circuit system only)
Theinstallationofspringparkingbrakesandtheirpipingarrangementsintoavehicleairbrakesystemwillvarydependingonthevehiclemake.
Springparkingbrakesmaybeinstalledonanairbrake–equippedvehicleforuseasareliableparkingbrakesystem.Intheservicebrakesystem,thebrakesareappliedbyairpressureandretractedbysprings.Inthespringparkingbrakesystem,thebrakesareappliedbyspringpressureandretractedbyairpressure.Thespringparkingbrakechambersareattachedtotheservicebrakechambersandoperatethroughthesamelinkage,thereforetheeffectivenessofthespringparkingbrakedependsontheservicebrakeadjustment.Thespringparkingbrakecontrolvalve(operatedbyasquare,yellowbutton)locatedinthecaballowsthedrivertoexhaustairoutofthespringparkingbrakecircuittoapplythebrakes,orpressurizethecircuittoreleasethem.Somesystemsmayhaveanadditionalvalvecontrolledbyabluebuttonthatappliesonlythetractorspringparkingbrakesandnotthetrailerspringparkingbrakes.Thesystemcanalsoactasanemergencybrake.Lossofairfromthesystemmayautomaticallyapplythebrakes.
Controlvalveswillvary,dependingonthemanufacturerandtypeofpipingarrangements.
Aspring–loadedvalverequiresthatthevalvebepushedintoreleasethespringparkingbrakes.Thisvalvecannotbeleftinthereleasedpositionwithairpressureinthesystembelowapproximately35psi.Anytimethereservoirpressuredropstoapproximately35psi,thisvalvewillcloseautomatically,placingthespringparkingbrakesintofullapplication.Onsomeoldervehiclestheremaybeasingletypeofpush–pullcontrolvalvethatdoesnothaveanautomaticreleasefeature.Toapplythespringparkingbrakes,thevalvemustbeoperatedmanually,eventhoughthereservoirpressurehasbeendepleted.
Duringnormaloperation,airpressurecages(compresses)thespring,holdingitreadyforparkingoremergencybraking.
32 • Air Brake Manual
Mounting Bolts
Spring parking brake
chamber
Service brake chamber
Clevis and pin
Push rod
Diaphragm
Dust cap
Brakes Off
Parking brake spring
Slack adjuster
Diaphragm return spring
Air Brake Manual • 33
Onthepre–tripairbrakeinspection(Section9),youmustensurethattheparkingbrakespringisnotmanuallycagedoritwillnotexpandandapplythebrake.Thebrakechambersshouldbecheckedforcracksanddamage.Thebrakechambershouldbefittedwithadustcaptoensuredebriswillnotenterthechamber.
Duringnormalservicebrakeoperation,theparkingbrakespringdoesnotexpand.Airpressurekeepsthespringcaged.
However,ittakesapproximately90psiofairpressuretokeepthespringscaged.Ifreservoirairpressureisallowedtodropbelow90psithespringswillstarttomove.Atapproximately70psithebrakeswillbepartiallyappliedmakingitdifficulttocontinuedriving.Iftheairpressuredropsbelow60psithebrakeswillbefullyappliedmakingitimpossibletomovethevehicleuntilairpressureisbuiltuptorecagethespringparkingbrakesorthespringsaremanuallycaged.
Springparkingbrakes(12),addedtothebrakechambersoftherearaxleonthesingleunitvehicle,areillustrated.Acontrolvalve(27)ismountedinthecab.Asupplylineofreservoirairispipedfromthedry
reservoirtothecontrolvalve.Openingthecontrolvalveallowsreservoirairpressuretoflowtothespringparkingbrakechambers,releasingthem.
Service Brakes Applied Brake On
12
12
27
Using a Spring Parking Brake
Mounting Bolts
Clevis and pin
Slack adjuster
Push rod
Diaphragm return spring
Diaphragm
Spring parking brake
chamber
Dust cap
Parking brake spring
Service brake chamber
34 • Air Brake Manual
Closingthecontrolvalveshutsoffthesupplyofreservoirairpressureandexhauststheexistingpressureinthespringparkingbrakechambers.Thismotionallowsthespringtoexpand,applyingthebrakes.
Caution:Parkingbrakesshouldbeinthereleasepositionbeforemakingaservicebrakeapplication.Afull–brakeapplication,madewhentheparkingbrakesareapplied,cancompoundtheforceexertedontheslackadjustersandlinkageandresultindamageorbrakefailure.Compoundingisthecombinationoftwoforces:theforceappliedbythespringbrakechamberandtheservicebrakechamber.
Springbrakesareprimarilyusedasaparkingbrake,butintheeventoflossofairpressureinthesystem,theycanassistinstoppingthevehicle.Howquicklytheywillstopthevehicledependsonsuchfactorsas:
• theweightandspeedofthevehicle;
• thesteepnessofthegrade;
• thespringforceofthespringbrakesthathavebeeninstalled;and,
• theadjustmentoftheservicebrakes.
Ifthebrakeshaveoverheated,suchasduringmountaindrivingorhardhighwaybraking,caremustbetakenwhenparkingthevehicle.Ifthespringparkingbrakesareappliedwhenthebrakedrumhasexpandedbecauseofextremeheating,whenthebrakedrumstartstocoolandcontract,thepressureexertedbythespringparkingbrakemaycausethebrakedrumtocrackorwarp.Whenparkingavehiclewithoverheatedbrakes,parkonlevelground,stoptheengineandleavethetransmissioninthelowestgearandblockthewheels.Donotsetthespringparkingbrakesuntilyouhaveverifiedthebrakedrumiscooltothetouch.
Mounting Bolts
Clevis and pin
Slack adjuster
Push rod
Diaphragm return spring
Diaphragm
Spring parking brake chamber
Dust cap
Parking brake springService brake chamber
Spring Parking Brakes Applied “Brakes On”
Air Brake Manual • 35
Mechanical Release (Caging)
Somespringparkingbrakescanbereleasedmechanicallyby“windingthemoff”or“caging”them.Cagingmeansthebrakesarebeingreleased.Thisisachievedwithaboltthatrunsthroughthecentreofthechamberbody,whichisturnedtocompressthespring.Itmaybenecessarytofirstremovealockplateandstudtogainaccesstotheheadofthebolt.Othertypeshaveadustcapthatmustfirstberemovedandaboltinserted.Insomecases,aspecialwrenchisrequired.Instructiononhowto“cage”isusuallyonthebodyoftheparkingbrakechamber.Ifallairislostandthevehiclehastobetowed,theparkingbrakescanbereleasedbycagingthem.Alwaysblockthewheelswhencagingtheparkingbrakespring.
Warning
Springparkingbrakechambersshouldneverbedisassembledwithoutfirstcompressingthespringwithacagingbolt.Thesespringsareunderextremepressureandcouldcauseseriouspersonalinjuryifdisassemblyisattemptedbyanyonenotexperiencedinservicingtheseunits.Disassemblyofaspringbrakechambershouldonlybepreformedbyaqualifiedmechanicortechnician.
Section Summary Questions
1. Whatismeantby“compounding”thebrakes?
2. Whyarespringbrakesareliabletypeofparkingbrake?
3. Howareparkingbrakesheldinthereleasedposition?
4. Whatarethefunctionsofthecab–mountedparkingbrakecontrolvalve?
5. Willparkingbrakesapply“automatically”inallbrakingsystems?
6. Whatisthereasonforreleasingtheparkingbrakesbeforemakingafullbrakeapplicationtest?
7. Whymustyoubecarefulparkingavehiclewithoverheatedbrakes?
8. Howcansometypesofparkingbrakesbereleasedwithouttheuseofairpressure?
9. Whatisthedangerofdisassemblingaspringparkingbrakeunit?
Mounting Bolts
Spring parking brake
chamber
Service brake chamber
Clevis and pin
Slack adjuster
Push rod
DiaphragmDiaphragm return spring
Caging bolt
Parking brake spring
Parking Brake Spring Caged “Brakes Off”
36 • Air Brake Manual
Notes
Air Brake Manual • 37 Air Brake Manual • 37
TrailerSystem
Section5
38 • Air Brake Manual
Uptothispoint,thesystemdiscussedistheairbrakesystemofatruckortractor.Ifatrailerwascoupledtoatruckortractor,thebrakesofthetrailerwouldhavetobeoperatedfromthetruckortractor.
Inthefollowingpagesthepowerunitofacombinationvehiclewillbereferredtoasatractor.
Glad Hands
Thistermreferstothecouplingdeviceusedtoconnectthecontrol(service)andsupply(emergency)linesofthetrailertothetractor.Thesecouplersconnecttogetherandlockinposition.Theyhaverubbergasketsthatpreventairfromescapingattheconnections.
Beforeconnectionismade,couplersshouldbecleanandfreeofdirtandgrit.Whenconnectingthegladhands,startwiththetwogasketstogetherandthecouplersata90°angletoeachother.Aquicksnapdownwardswilljoinandlockthecouplers.“Dead–end”couplersshouldbeusedwheneverthevehicleisdrivenwithoutatrailertopreventwateranddirtfromenteringthecouplerandlines.
Iftheunitisnotequippedwith“dead–end”couplers,thegladhandofthecontrol(service)linecanbelockedtothegladhandofthesupply(emergency)linetokeepwateranddirtfromenteringthelines.
Thecleanertheairsupplyiskept,thelesschanceofbrakeproblems.
Gladhandsandlinesshouldalsobesecuredtopreventthelinesfromchafingagainstvehiclecomponentsorbouncingoffthevehicle.Thiscouldseriouslydamagethegladhandsorlines.
Application Line
Theapplicationlineisreferredtoasacontrol(service)line.Thislineisconnectedtothefootandhandvalve.Whenthedriverdepressesthefootvalvetreadleapplicationairwillbedeliveredtothetractorbrakechambersandtothetrailerbrakechambers.Whenthedriverreleasesthefootvalvetreadle,theapplicationairtothetrailerbrakechambersmustreturntothefootvalvetobeexhaustedtotheatmosphere.
Thedisadvantagesofthissystemare:
• ifthetrailerbrokeawayfromthetractor,thetrailerwouldnothavebrakes.
• ifthecontrol(service)linepartedorruptured,thetrailerbrakeswouldnotbeapplied,andtheapplicationairwouldbelostfromthetractorifthebrakeswereapplied.
• iftheairpressureinthereservoirsislost,therewouldbenowaytoapplythebrakesofthetractororthetrailer.
• thetrailerbrakescannotbeappliedindependentlyfromthetractorandthereisnowaytosetthetrailerbrakeswhencouplingtothetractor.
• theapplicationandreleaseofthetrailerbrakeswouldbeslowerthanthoseofthetractor.
Thesedisadvantagesareovercomebytheadditionofthesupply(emergency)lineandvalvesdiscussedinthefollowingpages.
Theillustrationshowsthepipingofaunitwithbrakesapplied,similartothetandemaxlesofthetractor.Alsowithbrakesapplied,thetrailerhastandemaxlesequippedwithbrakechambers.
Theapplicationlinehasa“T”insertedbetweenthefootvalve(31)andthetractor’srelayvalve(13).Anairlinehasbeenconnectedfromthis“T”tothetrailerbyasetofcouplers(gladhands)(20).
Air line
Rubber seal
Air line
Air Brake Manual • 39
Thepurposeofthetrailerbrakehandvalve(30)istoallowthedrivertocontrolindependentlytheamountofapplicationairpressuretobedirectedtothetrailerbrakes.Italsoprovidesamethodofapplyingthetrailerbrakeswhencouplingthetrailertothetractor.
Thevalve,alsoallowsthedrivertoapplythetrailerbrakesindependentlyofthetractor.Theamountofapplicationairpressuredelivereddependsontheamountthevalveisopenedbythedriver.(Itcannotexceedthereservoirairpressure.)Somevalvesareequippedwithselfreturninghandles.
13 20“T”
31
Application Line
30
31
Trailer Brake Hand Valve
40 • Air Brake Manual
Note: Thetrailerbrakehandvalveisnottobeusedforparking,asairmaybleedoffiftheengineisstoppedorthehandvalvemovestothereleasedposition.
Thedriverhasappliedthebrakesbyusingthefootvalve(31).Applicationairisdirectedtothebrakechambersofthetractorandtothetrailerbrakesthroughatwo–waycheckvalve(26).Theshuttlehasshiftedtothelowpressureside,closingoffanyair
Two–Way Check Valves
Thepurposeofatwo–waycheckvalve(26)istodirectairflowintoacommonlinefromeitheroftwosources.Thisvalvewillpermitairtoflowfromthesourcethatissupplyingthehigherapplicationpressures.Theshuttlewillshiftsothatthehigherpressurewillbedirectedtothetrailerthroughthecontrol(service)line.Thisvalveislocatedbetweenthefoot–operatedvalveandthehand–operatedvalve.
flowtowardthehandvalveside.Thehandvalve(30)isintheclosedpositionandequalpressureisbeingappliedtothebrakechambersofthetractorandthebrakechambersofthetrailer.
30 26
31
Air from hand valve
Air from foot valve
To trailer
Shuttle
Foot Valve Application
Air Brake Manual • 41
Inthisillustrationwiththefootvalve(31)releasedandthehandvalve(30)opened,applicationairisdirectedfromthehandvalvethroughatwo–waycheckvalve(26),tothebrakechambers.Thetwo–waycheckvalveinthisapplicationhasshiftedtothelowpressureside,closingoffanyairflowtowardthefootvalveside.
Anytimeatrailerbrakeapplicationismadeusingthehandvalve,thedrivermaydepressthefootvalvetreadle.Ifthefootvalveapplicationisofahigherpressurethanthatofthehandvalve,thetwo–waycheckvalvewillshifttothelowerpressureside,allowingthehigherpressuretobedirectedtothetractorandtrailerbrakes.Duringafootvalveapplication,ifthedrivermakesahandvalveapplicationofahigherairpressure,thetwo–waycheckvalvewilldirectthehigherhandvalveairpressuretothetrailerbrakes.
Althoughthetrailerbrakesmaybeappliedindependentlybymeansofthehandvalve,themaximumapplicationpressurecanonlybethesameas,orslightlylessthan,reservoirpressure.
Tractor Protection System
Atractorprotectionsystempreventstotallossofairfromthetractorifthetrailerbreaksaway,oriftheconnectingairlinesbetweentractorandtrailerbecomeseparatedorruptured.Thetractorprotectionsystemconsistsoftwovalves:thetractorprotectionvalveandthetrailersupplyvalve.Othernamesforthetrailersupplyvalveare“trailersupplyvalve”and“emergencyvalve.”
Therearetwotypesoftrailersupplyvalves.Themostcommonistheautomatictrailersupplyvalve.Thisisaspring–loadedvalvethatisopenedmanuallyandheldopenbyairsystempressure.Onoldervehiclesyoumayfindamanualtrailersupplyvalve,whichmaybeatoggle–typeswitchorapush/pull–typevalve.
Tounderstandthefunctionofthetrailersupplyvalveandthetractorprotectionvalveinthesystem,itisimportanttounderstandhowtheyoperate.
30 26
31
Hand Valve Application
42 • Air Brake Manual
Tractor Protection Valve
Atractorprotectionvalve(24)isnormallylocatedneartherearofthetractorcabandhastwoairlinesrunningtoit,onefromthetrailersupplyvalve(28)andtheotherfromthetwo–waycheckvalve(26)fedbythehandorfootvalve.
Italsohastwoairlines:onegoingtothesupply(emergency)line(21),andonegoingtothecontrol(service)line(22).Thetractorprotectionvalveisspring–loadedandrequiresapproximately45psiinthesupply(emergency)linetoopenthevalve.Thisallowscontrol(service)airtopassthroughthecontrol(service)linetothetrailerwhilemakingabrakeapplication.Whenairlinesfromthetractorarecoupledtoatrailer,theopeningorclosingofthetrailersupplyvalveopensorclosesthetractorprotectionvalve.Disconnectingthesupply(emergency)linebetweenthetractorandtrailerwhilethetrailerischargedwillcauseanimmediatelossofpressureinthesupply(emergency)line.Thesuddenlossofairpressureinthelinewillcausethetrailersupplyvalvetoclose,andwithnoairpressureinthelinethetractorprotectionvalvewillclose.Whenthetractorprotectionvalueclosesitwillstoptheairflowtothecontrol(service)line.
Intheeventofacontrol(service)lineruptureordisconnectionbetweenthetractorandtrailernoactionorairlosswilltakeplaceuntilabrakeapplicationismade.Serviceairwillbelostoutofthedisconnectedorrupturedlinecausingthetractor’sairpressuretodrop.Atapproximately45psithetrailersupplyvalvewillclosecausinganemergencyapplicationofthetrailerbrakesandthetractorprotectionvalvetoclose.Thiswillstopthelossofserviceairatthedisconnectedline.
Thetractorprotectionvalvealsoprotectsthetractor’sserviceairfrombeinglostduringnormalbrakeapplicationswhileoperatingthetractorwithoutatrailer.
To the supply (emergency)
glad hand
To the control (service) glad
hand
Tractor Protection System (Open) (Trailer Charged)
Air from foot valve
Air from hand valve
Two–way check valve
(26)
Control (service) line (22)
Supply (emergency)
line (21)
Tractor protection valve (24)
Trailer supply valve (mounted in cab) (28)
Air from reservoir
Air Brake Manual • 43
Totesttheproperoperationofthetractorprotectionvalve,ensurethetractorspringparkingbrakesareappliedandthewheelsareblocked.Verifythesystemisatfullpressureandthetrailersupplyvalveisopen(trailercharged).Exitthecabanddisconnectthecontrol(service)andensurethatthereisnoairlossfromthecontrol(service)linegladhand.Enterthecab,ensurefullreservoirpressurebetween115psiand135psiandopenthetractorspringparkingbrakecontrolvalve.Shutofftheengineandmakeafullservicebrakeapplication.Airshouldescapefromthecontrol(service)linetonolowerthan20psi,thetractorprotectionvalvewillcloseandtheairlosswillstop.Releasetheservicebrakeapplication.Closethetractorspringparkingbrakecontrolvalveandensurethetrailersupplyvalveisclosed,ifnot,closemanually.Starttheengineandrebuildairpressure.Withairpressureatorabove90psi,makeatrailerservicebrakeapplicationwithtrailerhandvalve.Noairshouldescapefromthedisconnectedcontrol(service)line.Releasethebrakeapplication.Exitthecabandre–connectthecontrol(service)linegladhand.
Thisteststheproperopeningandclosingoperationofthespringportionofthetractorprotectionvalve.Atractorprotectionvalvewithabrokenreturnspringwillnotclosethevalveandwillcauselossofairduringnormalbrakeapplicationsifoperatingthetractorwithoutatrailer.
Trailer Supply Valve
Thetrailersupplyvalve(28)(usuallyaredoctagonalbutton)ismountedinthecabofthetractor.Thedriveropensthevalvebypushingorpullingthebutton,dependingonthetypeused.
Openingthevalvepermitsreservoirairpressuretoflowthrough.Thisairpressureispipedtothetractorprotectionvalveandthentothesupply(emergency)line.
Thevalveisspring–loadedandwillbeheldintheopenpositionwhensufficientpressureisreached.Iftheairpressuredropstoarangebetween45and20psi,thevalvewillcloseautomaticallybyspringpressure.Thedrivercanclosethevalvemanually,applyingthetrailerspringparkingbrakes.
Tractor Protection System (Closed) (Trailer Not Charged)
Air from foot valve
Air from hand valve
Two–way check valve
(26)
Control (service) line (22)
Supply (emergency)
line (21)
Tractor protection valve (24)
Trailer supply valve (mounted in cab) (28)
Air from reservoir
44 • Air Brake Manual
Automatic Trailer Supply Valve System
Thediagrambelowillustratesairbeingpipedfromthedryreservoirlinetothetrailersupplyvalve(28).Thetractorprotectionvalve(24)isfedbytwolines:onefromthetrailersupplyvalve(28)andonefrom
Inthediagramstheupperlineisthecontrol(service)line(22)andthelowerlineisthesupply(emergency)line(21).
Illustratedisatractorequippedwithatrailersupplyvalve(28)andatractorprotectionvalve(24).
thetwo–waycheckvalve(26).Leadingofffromthetractorprotectionvalvearetwolines,eachwithagladhandcoupler(20).Thesetwolinesarereferredtoasthecontrol(service)line(22)andthesupply(emergency)line(21).
Thetrailerisnotcoupledandthetractorisbeingoperatedalone(“bobtailing”).Thedriverhasnotopenedthetrailersupplyvalve(28)andthehandvalve(30)isclosed.
28 2624
22 21
30 28
31
2624
20
22 21
20
Air Brake Manual • 45
Inthisillustration,thedriverhasmadeabrakeapplicationwiththefootvalve(31)andapplicationairisbeingdeliveredtothetractorbrakechambers.Thetwo–waycheckvalve(26)hasshiftedtothelow
Ifthedriver,bymistake,appliedthehandvalve(30)withthetrailerdisconnected,theapplicationairdirectedtothetractorprotectionvalvewouldalsobe
pressureside,allowingapplicationairtoreachtheclosedtractorprotectionvalve(24).
Thereisnoairlossfromthetractorthroughthedisconnectedgladhands(20).
dead–ended.Again,noairlosswouldoccurifthetrailersupplyvalve(28)isintheclosedposition.
31
2624
30 28
20
31
2624
30 28
20
46 • Air Brake Manual
Inthisillustration,thetrailerhasbeencoupledtothetractor,andthecontrol(service)andsupply(emergency)lineshavebeencoupledusinggladhands(20).
Thetrailerunithasareservoir(16)installed.Thisreservoirwillprovideavolumeofairnearthetrailerbrakechambersfornormaloremergencybraking.Thetrailerreservoirisfittedwithadrainvalve(6),thesameasatractorreservoir.
Arelayemergencyvalve(39)ismountedonthetrailerreservoirortothetrailerframenearthebrakechambers.Therelayemergencyvalveservesthreemainfunctionsinthesystem:
1.Itrelaysairfromthetrailerreservoirtothetrailerbrakechambersduringabrakeapplication.Thispartofthevalveoperatesliketherelayvalvepreviouslydiscussed.Italsoprovidesaquickreleaseofthetrailerbrakes.
2.Itdirectstrailerreservoirairpressuretothetrailerbrakes,causinganemergencyapplicationofthebrakes.Thisactionwilloccurautomaticallyintheeventofrupturedorseparatedsupply(emergency)airlinebetweenthetractorandtrailer,orlossofairpressurefromthetractor.Arupturedcontrol(service)linewouldnotcauseanemergencybrakeapplication.Ifabrakeapplicationwasmadetherewouldbearapidlossoftractorreservoirair.Ifthebrakeapplicationwasheldtheairpressurewoulddroplowenoughtocauseanemergencyapplication.Thedriveratanytimemayoperatethecab–mountedtrailersupplyvalve(28)tocauseanemergencyapplicationofthetrailerbrakes.
3.Ithasaone–waycheckvalvewhichstopsairpressureinthetrailerreservoirfromgoingbacktothetractor.
20
166
39
28
Tractor and Trailer Coupled
Air Brake Manual • 47
Intheillustration,thecompressorhasraisedthereservoirairpressuretomaximum.
Thedriverhasopenedthetrailersupplyvalve(28)toallowthereservoirairpressuretobedirectedthroughthetractorprotectionvalve(24)tothetrailer.Theairpressurepassesthroughtherelayemergencyvalve(39)
Thisandthenextillustrationaretoonlyshowwhichbrakecomponentsandlinesareusedforafootvalveandhandvalveapplication.•Applicationwiththefootvalve(31)inorange.•Applicationwiththehandvalve(30)inbrown.Orangeandbrownareusedtoshowwhereairisappliedanddoesnotrepresentthesourceoftheair.Whenthefootvalveisdepressed,theapplicationair
tothereservoironthetrailer.Pressurewillbuildupinthetrailerreservoirtothesamepressureasthereservoirsonthetractor.Thisisknownas“charging”thetrailersystem.Thetrailersupplyvalveshouldonlybeopenwhenthetractorpressurehasbuiltuptoapproximately90psi,dependingonthevalve.
willbeappliedtothetractorbrakesandthetrailerbrakestogether.Aspreviouslyexplained,thetwo–waycheckvalve(26)hasshifted,andapplicationairisbeingdirectedthroughthetractorprotectionvalve(24)tothecontrol(service)line.Ifthefootvalveisreleasedandthehandvalveisapplied,theshuttleinthetwo–waycheckvalvewouldshiftandapplicationairwouldapplythetrailerbrakesonly.
31
24
30
26
39
2428
Charging the Trailer System
Foot or Hand Valve Brake Application
48 • Air Brake Manual
Applicationairdirectedfromeitherthefootorhandvalvecausescontrolpressuretomovethroughthecontrol(service)lineandactontherelayemergencyvalve(39).Thiscontrolpressurewillcausetherelayemergencyvalvetodirectairfromthetrailerreservoir(16)tothetrailerbrakechambers(14).Thepressuredirectedbytherelayemergencyvalvetothetrailerbrakechamberswillbethesameasthepressuredirectedtothetractorbrakechambers.Insuchasystem,brakelagtimehasbeenminimizedwiththeadditionofthetrailerreservoirandrelayemergencyvalve.
Releaseofthefootorhandvalvestopstheflowofapplicationair.Therelayportionofthevalvereturnstoitsoriginalposition,stoppingtheflowofairpressure.Theexhaustingportsofthevalveexhausttheairpressurefromthebrakechambers,releasingthebrakes.Inthissystem,thebrakesofboththetractorandtrailercanbereleasedquickly.
Caution:Trailerbrakesmustnotbeusedtoholdaparkedvehiclethatisleftunattended.Lossofpressurewillresultinlossofbrakes.Alwayssettheparkingbrake.
14
39
14
22 21
16
14
39
14
16
30
31
Emergency Application
Air Brake Manual • 49
Ifatrailerthatisnotequippedwithspringparkingbrakesweretoseparatefromthetractor,thecontrol(service)line(22)andthesupply(emergency)line(21)woulddetachfromthetractor.Thesuddenlossofairpressureinthesupply(emergency)linewilltriggertherelayemergencyvalve(39)whichcausesthetrailerreservoir(16)todumpitsairdirectlytothetrailerbrakechambers(14).Thisplacesthetrailerbrakesintoemergencyapplication.Thecheckvalveintherelay
Supply (Emergency) Line Rupture
Aruptureofthesupply(emergency)line(21)oranuncouplingofthesupply(emergency)linegladhandswilltriggerthesameactionasdescribedabove.
Control (Service) Line RuptureIfthecontrol(service)line(22)isrupturedordisconnected,noactionwilltakeplaceuntilabrakeapplicationismade.Whenitismadebyeitherthefootorhandvalve,theairlossfromthecontrol(service)linewilllowertheairpressureinthetractor’sreservoirsquickly,dependingontheamountofbrakingdemanded.Thisairlosswilleventuallyactivatethetractorprotectionsystemwhichinturnwillexhaustthetrailersupply(emergency)lineandcausethetrailerrelayemergencyvalvetoapplythetrailerbrakes.Itshouldbenotedthatanyproblemthatcauses
emergencyvalvewillclose,preventinganybleedbackofpressurefromthetrailerreservoir.Thelossofpressureinthetrailersupply(emergency)linewillcausethetractorprotectionsystemtosealoffthetractorleavingsufficientairpressuretobrakethetractor.
Thetrailerbrakeswillremainapplieduntileitherthepressureinthetrailerreservoirandlinesisdrainedoff,orthesupply(emergency)lineisrepairedandthesystemisrecharged.
aseveredropinreservoirpressureonthetractorsystem,willcausethelowwarningdevicetosignalthedriver.
Inthefollowingillustration,thecontrol(service)line(22)hasrupturedandthedriverismakingabrakeapplicationwiththefootvalve(31).Thetractorwillhavebrakesappliedbutthetrailerwillhavenobrakes.Ifthebrakeapplicationisheld,theairpressureinthetractorsystemwilllowertoadangerouslylowlevelandthenthetractorprotectionsystemwillplacethetrailerbrakesintoanemergencyapplication.
21
39
16
14
14
50 • Air Brake Manual
Ruptureofthecompressordischargelinewouldresultinlossofairpressurefromthesupply/wetreservoir(5).Whentheairpressureinthesupply/wetreservoir(5)ofthetractorfallsbelowthewarninglevel,duetoacompressorfailureorexcessiveleakageonthetractor,thewarningdeviceswillstarttooperate.Inthediagram,theone–waycheckvalve(7)haspreventedthereservoirairpressureintheprimary/dryreservoir(8)fromescapingbacktothesupply/wetreservoirandtherupturedline.
Thereissufficientreservoirairpressureintheprimary/dryreservoirforalimitednumberofbrakeapplicationstostopthevehiclebeforethespringparkingbrakesareactivated.(Thiswilldependonhowthespringparkingbrakesarepipedinthesystem.)
22
31
Control (Service) Line Rupture
5 7 8
Loss of Reservoir Air Pressure
Air Brake Manual • 51
Inthisillustrationthepressurehasbeenloweredtoapproximately45–20psiandthetractorprotectionsystemhasclosedautomatically,placingthetrailerbrakesintoanemergencyposition.Also,thespringparkingbrakessystemhashadtheairpressurereleasedactivatingthespringparkingbrakes.
Manual Trailer Supply Valve
Someoldertractorsmaybeequippedwithadifferenttypeofcab–mountedtrailersupplyvalvewhichmustbeoperatedmanuallybythedriver.Ithastwopositions:normalandemergency.
Thetractorwillbeequippedwithatractorprotectionvalve,andthetrailerunitwitharelayemergencyvalve,asintheprevioussystem.
Thefunctionsofthetrailersupplyvalve,tractorprotectionvalveandtherelayemergencyvalvewillbesimilartothoseexplainedpreviously.However,thereisoneimportantdifference.Intheeventoftractorreservoirairloss,thetrailersupplyvalvemustbeshiftedtotheemergencypositionmanuallytosealoffthetractor.
Thetruckprotectionsystemdescribedisanexampleofatractorequippedwithatypeofcab–mountedtrailersupplyvalve(28)whichwillcloseautomaticallywhentheairpressureinthesupply(emergency)line(21)dropsbelow45–20psi.Thevalvemayalsobeclosedmanually.
Anytimethedrivershiftsthecab–mountedtrailersupplyvalvetotheemergencyposition,andthetrailersystemischarged,thetrailersupplyvalvewillexhaustthesupply(emergency)line,whichcausesthetrailerreservoirtodumpitsairdirectlytothetrailerbrakechambers.
Thetrailerbrakeswillremainappliedonlyaslongasairpressureremainswithinthetrailersystem.Howlongtheairinthesystemwillholdthebrakesapplieddependsonhowairtightthesystemis.Asasafetyprecaution,parkedtrailerswithoutspringparkingbrakesshouldalwayshavethewheelsblockedtopreventapossiblerunaway.Tomoveatrailerthathasbeenparkedwiththebrakesinanemergencyapplication,itisnecessarytochargethesystemtoreleasethetrailerbrakes.
2128
Loss of Reservoir Air Pressure
52 • Air Brake Manual
Trailer Spring Parking Brakes
Springparkingbrakesarenowcommonlyfoundontrailers.Springparkingbrakesserveasameansofsecuringaparkedtrailerwhetheritisattachedtoatractorornot.Thespringparkingbrakesareappliedwithspringpressureandnotairpressure,sothereisnoriskoftheparkingbrakesreleasingandthetrailermoving.Theyalsoactasanemergencybrakingsystemifthetrailerweretobreakawayfromthetractororifthetractorlostadequateairpressure.
Atrailerwithspringparkingbrakeshasthesecomponents:
• frontandrearservicereservoirs(16)
• trailerspringbrakevalve(18)
• relayvalve(17)(thesameasonatractor—notanemergencyrelayvalveusedontrailerswithoutspringparkingbrakes)
• springparkingbrakechambers(15)(sameasonatractor)
Thetrailerspringbrakevalveisresponsibleforseveralimportantfunctions:
1. Itcontrolstheapplicationandreleaseofthetrailer’sspringbrakes.
2.Itprotectsandisolatesthefrontservicereservoirfromtherearservicereservoir.Thisisimportantasitpreventsanautomaticapplicationofthetrailerspringbrakesifoneofthereservoirsweretoloseairpressure.
3.Itpreventsautomaticspringbrakeapplicationifthetrailersupplylinehasagradualleak.
4.Itwillautomaticallyapplythespringparkingbrakesifsupplypressureisrapidlylost(ie:trailerbreakaway).
22
21
18 17
15
16
Section Summary Questions
1. Whatisthepurposeofatwo–waycheckvalve?
2. Whyshouldthegladhandsbeprotectedwhennotinuse?
3. Howcanadrivercontrolthetrailerbrakesindependently?
4. Shouldthehandvalvebeusedforparking?
5. Whatisthepurposeofthetractorprotectionvalve?
6. Howcanyoutesttheproperfunctionofthetractorprotectionvalve?
7. Whatisthepurposeofthetrailersupplyvalve?
8. Namethreefunctionsoftherelayemergencyvalve.
9. Describethefunctionofthesupply(emergency)line.
10. Describethefunctionofthecontrol(service)line.
11. Whatwilloccurifthesupply(emergency)lineruptures?
12. Whatwilloccurifthecontrol(service)lineruptures?
13. Whatwilloccurifabrakeapplicationismadewitharupturedcontrol(service)line?
14. Ifthefootvalveandthehandvalveareoperatedatthesametime,cantheapplicationairpressurebegreaterthanthereservoirairpressure?
15. Whyisatrailerequippedwithspringparkingbrakes?
16. Whatbrakecomponentsareonatrailerequippedwithspringparkingbrakes?
17. Whatarethefourfunctionsofthetrailerspringbrakevalve?
Air Brake Manual • 53
DualAirBrakeSystem
Section6
54 • Air Brake Manual
Basic Dual Air Brake System
Mostairbrakeequippedvehiclesontheroadtodayareusingadualairbrakesystem.Thesystemhasbeendevelopedtoaccommodateamechanicallysecuredparkingbrakethatcanbeappliedintheeventofservicebrakefailure.Italsoaccommodatestheneedforamodulatedbrakingsystemshouldeitheroneofthetwosystemsfail.Itisactuallytwobrakesystemsinone,withmorereservoircapacityresultinginamuchsafersystem.Atfirstglance,thedualsystemmightseemcomplicated,butifyouunderstandthebasicairbrakesystemdescribedsofar,andifthedualsystem
isseparatedintobasicfunctions,itbecomesquitesimple.
Asitsnamesuggests,thedualsystemistwosystemsorcircuitsinone.Therearedifferentwaysofseparatingthetwopartsofthesystem.Onatwo–axlevehicle,onecircuitoperatestherearaxleandtheothercircuitoperatesthefrontaxle.Ifonecircuithasafailure,theothercircuitisisolatedandwillcontinuetooperate.
Air Brake Manual • 55
Intheillustration,airispumpedbythecompressor(1)tothesupply/wetreservoir(5)(blue),whichisprotectedfromoverpressurizationbyasafetyvalve(4).Pressurizedairmovesfromthesupply/wetreservoirtotheprimary/dryreservoir(8)(green)andthesecondary/dryreservoir(10)(red)throughone–waycheckvalves(7).Atthispoint,thedualcircuitsstart.Airfromtheprimary/dryreservoirisdirectedtothefootvalve(31).Airisalsodirectedfromthesecondary/dryreservoirtothefootvalve.Thefootvalveissimilartotheonedescribedearlierinthebasicairbrakesystem,butisdividedintotwosections(twofootvalvesinone).Onesectionofthisdualfootvalvecontrolstheprimarycircuitandtheothercontrolsthesecondarycircuit.Whenabrakeapplicationismade,airisdrawnfromtheprimaryreservoirthroughthefootvalveandispassedontotherearbrakechambers.Atthesametime,airisalsodrawnfromthesecondaryreservoir,passesthroughthefootvalveandispassedontothefrontbrakechambers.Ifthereisairlossineithercircuit,theotherwillcontinuetooperateindependently.Unlessairislostinbothcircuits,thevehiclewillcontinuetohavebrakingability.Theprimaryandsecondarycircuitsareequippedwithlowairpressurewarningdevices,whicharetriggeredbythelowairpressureindicatorswitch(9)andreservoirairpressuregauges(29)locatedonthedashofthevehicle.
1 4 5 7 98 10
31
29
Treadle
Supply ports
Exhaust port
Delivery ports
Dual–Circuit Foot Valve
Dual Air Brake System
56 • Air Brake Manual
Whenspringbrakesareaddedtoadualairbrakesystem,thesametypeofdashcontrolvalvediscussedpreviouslyisused.Blendedairisusedtosupplythespringparkingbrakecontrolvalve(27).Blendedairisairtakenfromtheprimaryandsecondarycircuits
throughatwo–waycheckvalve(26).Withthispipingarrangementthevehiclecanhaveafailureineithercircuitwithoutthespringbrakesapplyingautomatically.Ifairislostinbothcircuits,thespringbrakeswillapply.
27 26
Dual Air Brake System with Spring Parking Brakes
Air Brake Manual • 57
Springparkingbrakesinthissystemservetwopurposes:first,asaparkingbrake,andsecondasanemergencybrakingsystem.Ifafailureoccursintheprimarycircuit(green),andabrakeapplicationismade,controlairfromthefootvalveisdirectedtoaspringbrakemodulatorvalve(23).Asthereisnosupplyairtomaintainbalanceinthemodulatorvalve,becauseoftheprimarycircuitfailure,themodulatorvalvethenexhaustsairpressurefromthespringparkingbrakecircuit.Theamountofairreleasedisequaltotheamountofairappliedbythefootvalve.Thereleaseofairinthespringparkingbrakecircuitcausesthedriveaxletobrakeusingspringpressure(12).
Whenthebrakesarereleased,supplyairfromthesecondarycircuit(red)returnsthespringparkingbrakestoanoffposition.Brakeapplicationscanberepeateduntilalltheairfromthesecondarycircuitislost.Howeverastheairpressuredropsbelow85psi,thespringparkingbrakeswon’treturntothefulloffposition,infacttheywillstarttodrag.Atapproximately35psi,thespringparkingbrakecontrolvalve(27)onthedashwillexhausttheremainingairinthesecondarycircuit,andthespringparkingbrakesarefullyapplied.Theonlywaythevehiclecanbemovedafterallairislostistorepairthedamagedcircuitandrechargethesystem,orcagethespringparkingbrakesystem.
27 23 12
12
Spring Parking Brakes with Modulator Valve
58 • Air Brake Manual
Combination Tractor and Trailer with Spring Parking Brakes
Thetrailersystemissuppliedbyblendedtractorairtakenfromtheprimaryandsecondarycircuitsthroughatwo–waycheckvalveaspreviouslydescribed.
Thesystemischargedbyopeningthetrailersupplyvalve(28),allowingairfromthetractortopassthroughthetractorprotectionvalve(24)andthetrailerspringbrakevalve(18)directlyintothetrailerspringparkingbrakechambers(15).Whenairenters,thepressureprotectionpartofthetrailerspringbrakevalveopens,allowingtheairtofillthetrailerreservoirs.Thetrailerspringbrakeswillnotreleaseuntilthereservoirpressureonthetrailerisadequate.
Whenabrakeapplicationismade,blendedcontrolairactsontherelayvalve(17),whichreleasesairfromthetrailerreservoirtothebrakechambers.
Inadualairbrakesystem,ifonecircuitdevelopsaleak,theothercircuitwouldbeprotectedfromairpressurelossbythetwo–waycheckvalve(26).
Ifthetrailerbreaksawayfromthetractor,thecontrol(service)andsupply(emergency)lineswillbepulledapart.Thesuddenlossofairinthesupply(emergency)linewillcausethetrailersupplyvalvetoclose,whichwillcausethetractorprotectionvalvetoclose,preventingairfromescapingoutofeitherbrokenconnection.Theairsupplyinthetractorissealedoffandisavailabletocontrolthetractorbrakes.Atthesameinstant,thesuddenlossofairinthesupply(emergency)linecausesthetrailerspringparkingbrakevalvetoexhausttheairfromthe
trailerspringparkingbrakechambers,applyingthetrailerbrakes.Thetrailerbrakescannotbereleasedundertheseconditionsunlessthelinesarere–coupledandthetrailerreservoirsrecharged.
Ifonlythesupply(emergency)linebreaksbetweentractorandtrailer,thesamesequenceofeventswilloccur.
Abreakorruptureinthecontrol(service)linewillnotaffectthetraileruntilabrakeapplicationismade.Alossofpressureinthetractorsystemwillthenresult,ifpressureisallowedtodroplowenoughitwillcausethesameemergencybrakeapplicationdescribedabove.However,thedriverwillbeabletoreleasethespringparkingbrakesbyreleasingthefootvalve,rebuildingairpressureandopeningthetrailersupplyvalve.
Toapplythespringparkingbrakes,thespringparkingbrakecontrolvalve(27)isclosed,causingalossofairpressureinthelinewhichappliesthespringparkingbrakesasdescribedabove.
Theoldandnewtractorandtrailersystemsarefullyinterchangeable,whethertheyareadualairbrakesystemorbasicairbrakesystem,andwhethertheyaresystemswithorwithoutspringparkingbrakes.
28 18 15
15
17
242627
Air Brake Manual • 59
Section Summary Questions
1. Whatisthebasicprincipleofthedualairbrakesystem?
2. Whatvalveisusedtoprotecttheprimarycircuitfromthesecondarycircuit?
3. Inadualairbrakesystem,willthevehiclecontinuetohavebrakingabilityifonecircuitfails?
4. Isthereadifferencebetweenthefootvalveusedinabasicairbrakesystemandthefootvalveusedinthedualairbrakesystem?
5. Nametwofunctionsofthespringparkingbrakesinadualairbrakesystem.
6. Describethefunctionsofthespringbrakemodulatorvalve.
7. Ifthetrailerbreaksawayfromthetractoronadualairbrakesystem,whatappliesthebrakesonthetrailer?
8. Whatisblendedair?
9. Canatrailerwithabasicairbrakesystembetowedbyatractorwithadualairbrakesystem?
60 • Air Brake Manual
Notes
Air Brake Manual • 61
ElectronicControlledBrakingand
TractionSystems
Section7
WheelAxle
62 • Air Brake Manual
Anti–Lock Brake System (ABS)
Ananti–lockbrakesystemisanelectronicsystemthatmonitorswheelspeedatalltimesandcontrolswheelspeedwhilebraking.Ifitdetectsawheellocking–upduringabrakeapplication,thesystemreleasesbrakepressuretothatwheelonly.Thiskeepsthewheelfromskiddingandincreasesvehiclestabilityandcontrolduringemergencystopsandinadversesituationssuchasonwetoriceslickedroads,throughcurvesorduringlanechanges.TheairbrakesystemremainsthesamewiththeadditionoftheABScomponents.
AnABSbasicallyconsistsof:
• Anelectroniccontrolunit(ECU)
• Awheelsensorandtoothwheel
• ABSvalves
TheECUisthebrainofthesystem.Thewheelsensorsarelocatedonaminimumoftwo,oruptoallsixsetsofwheels,dependingonthesystem.ThewheelsensorsconstantlysendinformationtotheECU.Whenabrakeapplicationismadeandthesystemdetectsawheellocking–up,theECUsendsamessagetotheABSvalvestoreleasebrakepressureonthatparticularwheelpreventinglockup.Usuallythereisawarninglightlocatedonthedashtoinformthedriverofthesystemoperation.Everydrivershouldhavefullunderstandingofthewarninglightoperationforthevehicletheydrive.
WhendrivingavehiclewithABSapplythebrakesnormally.WhentheABSstartsworking,donotreleasethepressureyouhaveappliedtothebrakepedal.AvoidpumpingthebrakepedalastheABSautomaticallyappliesandreleasesthebrakesuptofivetimesasecondwhichismuchfasterthanyoucanpumpthebrakepedal.ForoptimumABSoperation,thedrivershouldmakeabrakeapplicationandhold,allowingtheABStocontrolbrakingpressureateachwheel.
Whenusinganenginebrakeandyouencounteraslipperyroadsurface,theABSwilldetectthewheellockupandautomaticallyturnofftheenginebrakeuntiltractionisregained,thenresumeenginebraking.
Forinformationspecifictothevehicleyoudrive,refertotheoperator’smanual.
TrailersmayalsobeequippedwithABSandthesystemwilloperatemuchthesameasonthetractor.However,trailerswithABSwillhaveasystemwarninglighttypicallymountedonthetrailer’sleftfrontcorner,visibleintheleftsidemirror.Onsomesystemstheymayhaveanextrawarninglightonthedashofthetractor.
TractorsandtrailerswithorwithoutABScanbeconnectedtooneanotherwithoutaffectingtheoperationoftheairbrakesystem.
Tooth Wheel and Sensor Block
Air Brake Manual • 63
Four Sensor–Four Modulator Valve Anti–Lock Brake System
E.C.U.
Relay block
Tooth wheel and sensor block
Tooth wheel and
sensor block
Modulator valves
Modulator valves
Brake chambers
Brake chambers
Brake pedalBrake
chambers
Dash lamp
Tooth wheel and sensor block
Tooth wheel and sensor block
64 • Air Brake Manual
Automatic Traction Control (ATC)
Automatictractioncontrolisanelectronicsystemthatmonitorswheelspinonaccelerationandusescontrolledbrakingtogaintraction.Thissystemreducesthepotentialofpoweringintoajackknifecausedbywheeloverspinduringacceleration,alongwithimprovingtheabilityofthedrivertomanoeuvrethevehicleonslipperysurfacesthroughcurvesandlanechanges.ATCisanoptiononlyavailableonvehiclesequippedwithABS.
Thesystemusestwofunctions:differentialbrakingandelectronicenginecontrol.
DifferentialbrakingoccurswhenadrivewheelbeginstospincausingtheATCtoautomaticallyapplythebrakeonthatwheelandtransferpowertotheotherdrivingwheels.
Differentialbrakingisactivatedwhenthesystemdetectsawheelslippingbecausethewheelsareoperatingondifferentsurfacessuchasonewheelondrypavementandtheotheronice.
ElectronicenginecontrolisactivatedautomaticallybytheATCifallthewheelsbegintoslip.Enginepowerisreducedtoattainoptimumtire–to–roadtractionwithoutdriverintervention.Whenavehicleisbeingoperatedwiththecruisecontrolsetandwheelslipisdetected,theATCwillautomaticallycancelthecruisecontrolsetting.Thiswillaidthedriverinmaintainingcontrol.Cruisecontrolshouldnotbeusedonslipperysurfaces.
Awarninglightislocatedonthedashtoinformthedriverwhenwheelslipisdetected.TheATCsystemusesmanyofthesamesensingandcontrolcomponentsastheanti–lockbrakesystem.Forinformationspecifictothevehicleyoudrive,refertotheoperator’smanual.
Section Summary Questions
1. Whatisthepurposeoftheanti–lockbrakesystem?
2. Whatthreecomponentsdoesananti–lockbrakesystemconsistof?
3. Howshouldyouapplythebrakeswhenbrakingonwetoricyroadsinavehicleequippedwithanti–lockbrakes?
4. Canatrailerwithanti–lockbrakesbeconnectedtoatractorwithoutanti–lockbrakesystem?
5. Whatisthepurposeoftheautomatictractioncontrolsystem?
6. Whattwofunctionsdoesthesystemusetocontroltraction?
Air Brake Manual • 65
BrakeAdjustmentandIn–ServiceCheck
Section8
66 • Air Brake Manual
Brake AdjustmentOnvehiclesequippedwithhydraulicbrakesitispossibletopumpthebrakepedaltocompensateforbrakesthatareoutofadjustment.Thisisnotpossiblewithavehicleequippedwithanairbrakesystemwithmanualslackadjusters.Whenthebrakesareadjustedbyslackadjusters,theshoesaremovedtowardthedrum.Thisbringsthemasclosetothedrumsaspossibleminimizingtheamountoffreetravelwhenthebrakesareapplied.Italsoreducesthevolumeofairusedtoapplythebrakes.
Brakeadjustment(pushrodtravel)mustbecheckedaspartofthepre–tripairbrakeinspection(Section9).
Yourcompanymayhaveamaintenancecrewtokeepvehiclessafelyrunning.Butonepersonaloneisultimatelyresponsibletoensurethatthebrakesareoperatingproperlybeforethevehicleismoved.Thatpersonisthedriver.
Brake Adjustment–It’s CriticalThemostimportantpartofanybrakingsystemisthefoundationbrakes.Ifthesearenotincorrectworkingorderandproperlyadjusted,thebestdesignedairbrakesystemwon’tbeabletosafelystopthevehicle.
Unfortunately,brakeadjustmentisoftenneglected.Therealityisthatbrakefailuresandrunawaysthatresultincrashesarealmostnevercausedbyanairsystemfailure,butbytheabsenceofroutinebrakemaintenance,orbythedriverfailingtocheckbrakesonadailybasis.
Dailypre–andpost–tripinspectionsaremandatory.Thedrivermaybeheldresponsibleifthebrakesareincorrectlyadjustedornotworkingproperly.
Brake Adjustment–It’s the LawFederalandprovinciallawsrequirethatmanualandautomaticslackadjustersbecheckeddaily,duringthepre–tripinspection.Itisuptoyou,theprofessionaldriver,toensureyourvehiclehassafe,correctlyadjustedbrakes.Youthedriver,canbefinedifthebrakesonthevehicleyouaredrivingarefoundtobeoutofadjustment.
You’realsorequiredbylawtocheckyourbrakesbeforedrivingdownsteepgradesthatarepostedwithregulatorysigns.
Youcan’talwayscrawlunderneathyourvehicletomeasureairbrakechamberpushrodtravel,buttherearedevicesavailabletohelpyouvisuallycheckforbrakeadjustment.
Air Brake Manual • 67
DefinitionSlackadjustmentmeansadjustingthebrakestokeepairchamberpushrodtravelwithintolerancetoensurethatthebrakesareeffective.
Pushrodtravelmeansthedistancethepushrodextendsfromtheairbrakechamberwhenthebrakesareapplied.
S–Cam Brake–Released
A�typical�s–cam�brake.��The�brake�is�shown�in�the�released�position.
ThemostcommontypeofairbrakechamberusedontrucksandtrailersistheType30.Thesechambershaveamaximumavailablestrokeof2Minches.AlongstrokeType30isdesignatedType30LS,andhasamaximumavailablestrokeofthreeinches.
S-Cam Brake–Applied
A�typical�s–cam�brake.��The�brake�is�shown�in�the�applied�position.
Inthisdiagram,thebrakeshavebeenappliedandthebrakeliningshavecontactedthebrakedrum.ThebrakechamberhasstrokedlessthanMofitsmaximumstroke,indicatingthatthebrakeisincorrectadjustment.
Eachbrakeonanaxleshouldbeadjustedtohaveasimilaramountofpushrodtravel—thatis,thepushrodtraveloftheleftbrakeshouldbesimilartothepushrodtraveloftherightbrakeontheaxle.
68 • Air Brake Manual
S–Cam Brake–Incorrectly Adjusted and Cold Brake Drum
Check�air�brake�chamber��pushrod�travel�at�least�daily.
Inthisdiagram,thebrakesareappliedandtheliningshavecontactedthebrakedrum.
This�brake�chamber�pushrod�has�excessive�travel,��but�may�work�as�long�as�the�brake�drum�is�cool.��But�it�won’t�stay�cool�for�long!
NotethatthebrakechamberhasstrokedmorethanMofitsmaximum,whichmeansthatthisairbrakechamberpushrodhasexcessivetravelandthebrakesareinneedofadjustment.
Whenthebrakedrumiscoolandwithnormalbrakeapplicationpressure,thebrakewillseemtobeeffective,soitiseasytobelulledintoafalsesenseofsecurity.
Airbrakeequippedvehiclesrarely“lose”theirbrakes.Rather,brakefailureoccursbecausethedriverhasfailedtocheckandcorrectlyadjustthebrakes.
S–Cam Brake–Incorrectly Adjusted and Hot Brake Drum
Now�that�the�brake�drum�is�hot,�the�brake�linings�will�no�longer��contact�the�drum.�The�brake�chamber�has�bottomed�out.
Thisdiagramshowsthesamebrakeafterafewbrakeapplications.
Castironbrakedrumsexpandwhenheated,causingtheairchambertostrokefurtherandfurtherasthetemperaturerises.
Ifanunforeseeneventrequiredthedrivertomakeasuddenstop,thebrakechambercouldbottomout,andbrakingpowerwouldbegreatlyreduced.
Onlongdowngrades,theexpansionofhotbrakedrumscancauseatotallossofbrakingandresultinarunaway.
Evenincorrectlyadjustedbrakesmayseemtoworkwhenbrakesarelightlyapplied.
Thiscouldresultinbrakefadeundermoderatetoheavybraking,oronadownhill.
Air Brake Manual • 69
Checking and Adjusting S–Cam Brakes–Manual Slack AdjustersDriversseldomhavetheluxuryofhavingtheuseofapitandhydraulicjackssothatbrakeadjustmentcanbedonewithwheelsofftheground.However,brakescanstillbeadjustedveryaccuratelywiththewheelsonthegroundusingoneofthefollowingmethods.
Besurethatthevehicleissafelyparkedwiththewheelsblocked.Theairsystemshouldbeatfullpressureandthespringparkingbrakesreleased.Turntheengineoffsothatyoucanlistenforairleaks.
Therearetwomethodsofcheckingforcorrectadjustment,butthemeasurementsthatindicatetheneedforadjustmentaredifferent.
Pry Method of Free Stroke Measurement
Thispictureshowsthecommonmethodofcheckingthefreestrokeofthepushrod:
Using�a�brake�tool�to�measure�air�brake��chamber�pushrod�free�stroke.
Makesureyouhavetheproperequipmenttocheckandadjustthebrakes.Youwillneed:
•Awrench
•Amarkertomeasurepushrodtravel
•Sturdyclothingsuitableforcrawlingunderthevehicle
•Aflashlight
Youshouldalsoweareyeprotectionandabumpcap.
Tobegin,makesuresystemairpressureisatleast90–100psiandallparkingbrakesarereleased.
1. Makeamarkonthepushrodwhereitexitsthebrakechamber.
Note:Itissometimesdifficulttomarkthepushrodatthislocation.Alternatively,markthecentreoftheclevispinontheslackadjusterarm.
2. Pullthepushrodoutfromthebrakechamber,usingatoolforleverage.
3. MeasurethedistancebetweenthechalkmarkandthefaceofthebrakechamberMtoPofaninchoffreestrokeisagoodrangeforatype30standardstrokebrakechamber.IfthisdistanceismorethanPofaninch,thebrakesneedadjustment.
70 • Air Brake Manual
Applied Stroke Method (service brake application)Theappliedstroke(brakeapplication)methodrequirestwopeople—onetoapplythebrakesandonetomeasuretravel.
Ifyouhaveadevicetoapplyandholdtheservicebrakeson,youcanusethebrakeapplicationmethodwithoutneedinganotherperson.
Checking�the�pushrod�stroke��by�applying�the�brakes.
Brake Adjustment IndicatorsNewairbrakechamberpushrodshaveamarking(usuallyred)toindicatewhenbrakeadjustmentmustbedoneimmediately.Ifthepushrodtravelbecomesexcessive,themarkingwillshow.
Don’twaituntiltheredmarkingisexposedbeforeadjustingthebrakes.
If�the�red�marking�on�the�pushrod�(at�the�chamber�face)�is�visible,��it�indicates�that�the�brake�is�dangerously�out�of�adjustment��and�it�needs�immediate�attention.
Theappliedstrokemethodisthepreferredmethodandisalsoamethodrecommendedbycommercialfleetmaintenancesupervisors.
1. Withthebrakesreleased,makeamarkwherethepushrodexitsthebrakechamber.
2. Withtheengineoff,makeaseriesofbrakeapplicationstoreducethereservoirpressuretobetween90to100psi.
3. Applyandholdafullbrakeapplication(90to100psi).
4. Measurethedistancebetweenthemarkandthefaceofthebrakechamber.Thedifferencebetweenmeasurementsiscalledthechamberappliedstroke.
Whilecheckingairbrakeslookforotherbrakecomponentwearandexcessiveplayincluding:
•S–cambushingwear
•S–camsplinewear
•Slackadjusterplay(worngear)
•Clevispinwear
Air Brake Manual • 71
Brake Adjustment–Manual Slack Adjuster
WithatypicalType30standardstrokebrakechamber,youmustadjustthebrakesifpushrodtravelis:
•morethanPofaninchusingtheprymethodoffreestrokemeasurement,or
•morethan1 1/@inchesusingthebrakeapplication—appliedstrokemeasurementmethod.
Notethatthesearemaximummeasurements.Youshouldadjustthebrakesifyourmeasurementsapproachtheselimits.
AdjustmentMostmanualslackadjustershaveaspring–loadedlockingsleevethatmustbepressedinandheldsotheadjustingboltcanbeturned.
Dependingupontheorientationoftheslackadjuster,thecorrectdirectiontoturntheadjustingboltmaybeclockwiseorcounterclockwise.Watchtoensurethatyouaretighteningandnotlooseningtheslackadjustment.
Withawrenchofthepropersize,usuallya9/!^inch,depressthelockingsleeveandturntheadjustingboltwhilewatchingtheendofthecamshaft.Thecamshaftwillrotateslightlyastheboltisbeingturned.Ifyouareturningintherightdirection,thecamwillrotateinthesamedirectionthatitwouldifthebrakeswerebeingapplied,asshownbythearrowonthecamendinthediagrambelow.
The�push�rod�and�the�slack�adjuster�arm�should�never�move�away�from�the�brake�chamber�while�turning�the�adjusting�bolt.
Ifwhenturningtheadjustingbolt,theslackadjusterispullingthepushrodoutofthechamber,stop.Theadjustingboltisbeingturnedinthewrongdirection.
72 • Air Brake Manual
Oncetheproperdirectionisestablished,continueturninguntilsolidresistanceismet.Thisindicatesthatthebrakeliningshavecontactedthebrakedrum.
Ifthebrakehasnodustshields,orifyoucanseethebrakeshoesandliningsthroughaninspectionslot,youcanvisuallyverifythattheliningshavecontactedthedrum.
Backingofftheadjustingboltabout1/ #ofaturnshouldestablishcorrectrunningclearancebetweenthelininganddrum.Besurethelockingsleevere–engagestheboltsothattheadjustmentwillnotbackoff.
Itiscommon,especiallyontandemaxleunits,fortheadjustingboltsononeaxletoadjustinonedirection,whiletheotheraxlerequiresanoppositeturn.Itisnotuncommontofindthatthebrakesononeortheotheraxlehavebeenmistakenlybackedoff,creatingaserioussafetyhazard.
Afteradjusting,verifythatthereissufficientclearancebyagainpullingorpryingontheslackadjusterarm,andre–measuringthefreestroke,rememberthatMinchisideal.
Adjusting S–Cam Brakes with Automatic Slack Adjusters—Why—When—How
Automaticslackadjustersareentirelydifferentthanthemanualtypes.
Onceproperlyinstalled,automaticslackadjustersshouldnotneedmanualadjustment.Ifanautomaticslackadjusterisfoundtostrokebeyondthemaximumallowed,thisusuallyindicatesthattherearebrakeproblemsthatneedtoberepairedbyqualifiedbrakeservicepersonnel.
Automaticslackadjustersstillneedtoberegularlycheckedtoensurethatcorrectadjustmentisbeingmaintained.
Pushrodstrokeswithautomaticslackadjustersareusuallyslightlylongerthanwithwell–adjustedmanualslackadjusters.Whileamanualadjustmentmaytemporarilyshortenthestroke,theautomaticslackwillsoonre–settoitsdesignedstroke.
Manufacturersrecommendthatautomaticslackadjustersbecheckedbyamechanicateachchassislubricationinterval,orfrom40,000to80,000km.
However,theNationalSafetyCodeofCanada,aswellasfederalandstatelawsintheU.S.requireadailycheckofbrakeadjustmentaspartofapre-tripinspection.Also,incertainmountainousareasofNorthAmerica,trucksarerequiredtostopandcheckbrakesbeforeproceedingdownlonggrades.Thecheckingisrequiredregardlessofwhethermanualorautomaticslackadjustersareused.
Priortomanuallycheckingslackadjusterstroke,ensuretractorspringparkingbrakecontrolvalveandtrailersupplyvalveareopen.Ensurereservoirairpressureisabove90psiandmakeafullbrakeapplicationandrelease.Repeatthisprocess6times—thesebrakeapplicationswillbeadequatetocauseanautomaticslackadjustertoadjust.Alightbrakeapplicationwillnotcausetheadjustment.
Ifaftermaking6fullbrakeapplicationswithreservoirpressureabove90psi,apushrodstrokeisexcessive,theautomaticslackadjusterhaseitherfailed,beenincorrectlyinstalled,orthereisaproblemwithinthefoundationbrake.Manualadjustmentatthistimeisonlyastop–gapmeasuresothevehiclecanbedriventoaservicedepotforinspectionandpossiblereplacement.
Mostmanufacturersofautomaticslackadjustersspecifythatpushrodstrokebecheckedbymakinga90to100psiapplication.Ifyouhavenoapplicationpressuregauge,turntheengineoffandpumpthereservoirpressuredowntobetween90and100psi–thenmakeafullapplication.
Automaticslackadjustersshouldonlybeadjustedorrepairedbyaqualifiedmechanicexceptinanemergency.Followthemanufacturer’sinstructionsincarryingouranyadjustment.
Air Brake Manual • 73
Emergency Manual Brake Adjustment—Automatic Slack Adjusters
Ifthevehiclemustbedriventoaservicedepot,anemergencymanualadjustmentmaybedone.
THESE ARE EMERGENCY PROCEDURES ONLY. A REPAIR OR REPLACEMENT MUST BE MADE AS SOON AS POSSIBLE.
Besurethatthevehicleissafelyparkedwiththewheelsblocked.Theairsystemshouldbeatfullpressureandthespringparkingbrakesreleased.
WithatypicalType30standardstrokebrakechamber,youmustadjustthebrakesifpushrodmeasurementsare:
•morethanPofaninchusingtheprymethodoffreestrokemeasurement,or
•morethantwoinchesusingthebrakeapplication—appliedstrokemethod.
Four�types�of�automatic�slack�adjusters
Notethatthesearemaximummeasurements.Youshouldadjustthebrakesifyourmeasurementsapproachtheselimits.
Ifyoumakeanemergencyadjustmentofanautomaticslackadjuster,besuretorecorditonyourdailypost–tripinspectionreport.
Itisstronglyrecommendedthatyouobtaintheservicedatabooksforthemakeofautomaticslackadjustersthatyouareusing.Theycontainalltheinformationneededtokeepthemoperatingproperly,includinglubricationrequirements,initialsetup,inspectionandtesting.Theyareavailablewheretruckpartsaresold.
74 • Air Brake Manual
Slack Adjusters with Hexagonal Adjusting Bolts
Iftheslackadjusterhasahexagonal(six-sided)adjustingbolt,thebrakesmaybesetupbyturningtheadjustingboltinaclockwisedirectionuntiltheliningcontactsthedrum.BackingofftheadjustingboltbyMaturnshouldrestorerunningclearance.Backingoffmaytakeconsiderableforceandmaybeaccompaniedbyaratchetingsoundandfeel.Thisisnormal.
These�two�types�of�automatic�slack�adjusters�both�have�hexagonal�adjusting�bolts.
Slack Adjusters with Square Adjusting Bolts
Iftheslackadjusterhasasquareadjustingboltlocatedatthebottomendofthebody,donotattemptadjustinguntilaspring–loadedpawlthatmesheswithinternalteethisdisengaged.TheseunitshaveaPinchhexagonal(hex)caplocatedontheslackadjusterbody.Someofthesehexcapsareequippedwitharound“button”thatcanbepriedupapproximately1/ #@ofaninchandheld,usingascrewdriver.Onunitsnotequippedwiththebutton,thehexcap,springandpawlmustberemoved.Withthespringandpawldisengaged,anadjustmentcanbemade.
Thesebrakesmustbesetupwithacounter–clockwiseturnuntiltheliningcontactsthedrum.TurningtheadjustingboltMaturnclockwisewillrestorerunningclearance.Releasethebuttonorre–installthespringandpawliftheywereremoved.
This�type�of�slack�adjuster�has�a�square�adjusting�bolt.
Air Brake Manual • 75
Disc Brake Adjustment
Thereareanumberofmakesandmodelsofairdiscbrakes,eachwithadifferentadjustmentprocedure.Itisthereforerecommendedthatyouconsultthemanufacturer’smanualforadjustmentorservice.
Wedge Brake Adjustment
Manualadjusters:
• Hoistorjackwheelsofftheground.
• Removedustcoverfromadjustingslotsattwoplacesoneachbrake.Ontwinchamberunitstheadjustingslotsareinthebackingplatebelowtheforwardchamberandabovetherearchamber.Ifstarwheeladjustingboltsarenotfoundatthesepositions,thebrakehasbeenassembledonthewrongsideofthevehicle.Thesinglechamberunitshaveadjustingslotsinthebackingplateoneachsideofthechamber.
• Adjustingboltshaveright–handthreads.Turningthewheelbyhand,useanadjustingspoontoturnthestarwheeluntiltheshoedevelopsaheavydragonthedrum.Thenbackoffthebolttoaverylightdragonthedrum.
• Repeatfortheothershoeonthatbrakeassembly.
• Replacethedustcoversintheadjustingslots.
• Repeattheabovestepsontheotherbrakeassemblies.
There is no reliable substitute for physically checking brake adjustment.
After a Brake Adjustment
Atthefirststopafteradjustingthebrakes,checkeachbrakedrumorrotorfortemperature.Anextrahotbrakedrumindicatesthatyouhaveoveradjustedit.
Onlywhenallbrakesareproperlyadjustedwillthesystembeabletoabsorbtherequiredamountofenergytobringtheloadedvehicletoasafestopunderextremeconditions.Rememberthatpoorlyadjustedbrakesmayappeartobeworkingatslowspeedsonlightairapplication.Theonlywaytobesureyourvehiclebrakesareproperlyadjustedistophysicallycheckthepushrodtravelateachwheel.
76 • Air Brake Manual
In–Service Checks
Insomeareassignsarepostedinadvanceofsteeporlongdowngrades.Thesesignsindicatethatthedrivermuststopthevehicleinthepulloutareaandinspectthebrakingsystembeforeproceeding.Checkthat:
• thecompressorismaintainingfullreservoirairpressure;
• pushrodtraveliswithinlimitationsonallchambers;
• therearenoairleaks;
• thegladhandsandthelinesaresecure;
• thedrums,bearingsandtiresarenotoverheating;
• thetrailersupplyvalveisoperatingproperly.
Thisshouldbeusedasanin–servicecheckonlyandnotmistakenasadailypre–tripairbrakeinspection.
Thedrivermustbeawareoftheconditionofthevehicle’sbrakingsystematalltimes.Thiscanbedoneby:
• watchingthepressuregauges;
• hearingthewarningsignals;and
• feelingthebrakingresponseofthevehicle.
Bythismethodofobservation,thedrivershouldbeabletonoticeanydefectsdevelopinginthebrakingsystemandbeawarethatserviceoradjustmentisrequired.
Maintenance and Servicing of the Air Brake System
Ensuringthatthevehicleisinproperconditiontodriveistheresponsibilityofeveryoneinvolved.
Preventivemaintenancechecksaredesignedtopreventmechanicalfailuresthatcouldresultfromneglect.Thesecheckscutrepaircostsbydetectingminormechanicaldefectswhichwouldotherwisedevelopintomajorbreakdowns.
Preventivemaintenancemaybeassignedtoamaintenancecrewortothedriver.Howeverthedrivermustensurethatthebrakingsystemisinsafeoperatingconditionbeforethevehiclemoves.
Air Brake Manual • 77
Air Brake Adjustment Myths
There�is�some�misinformation�about�air�brakes�that�you�may�hear.�Most�of�this�is�not�critical,�but�the�following�three�myths�could�be�dangerous,�if�believed.
Myth#1:Brakeadjustmentcanbecheckedfromthecabbymakingafullbrakeapplicationandcheckingforaninitialpressuredropofbetween8–12psi.Theassumptionisthatasthebrakechambersstrokefurtherandfurther,thatmoreairvolumewillberequired,andthisshouldshowuponthereservoirgauges.
Fact #1:Modern trucks have very large air reservoirs, and even if all the brakes had excess pushrod travel, the pressure drop would not reach the 8–12 psi range. Also, most truck reservoir gauges do not have markings fine enough to accurately estimate such pressure changes.
Myth#2:Withthebrakesapplied,a90-degreeanglebetweenthecentreoftheslackadjusterarmandthechamberpushrodisagoodindicationthatthebrakeisincorrectadjustment.
Fact #2: The 90-degree angle is more dependent on the length of the chamber pushrod than on brake adjustment. Also, to prevent interference between the slack adjuster and suspension parts, some manufacturers will vary the angle up to plus or minus 10 degrees.
Myth#3:Aclockwiseturnoftheadjustingboltonamanualslackadjusterwillsetupthebrakes.
Fact #3: Depending on the orientation of the slack adjuster on the brake assembly, the correct direction to set up the brakes may be clockwise, or counter-clockwise. On vehicles with tandem axles, it is common to find that one axle sets up with a clockwise turn, while the other requires a reverse direction.
78 • Air Brake Manual
Section Summary Questions
1. Whyisitsocriticaltocheckslackadjustment?
2. Whoisultimatelyresponsibleforthebrakesonavehicle?
3. Whowillbefinedforoperatingavehiclewithbrakesimproperlyadjusted?
4. Whatarethedangersofoperatingavehiclewherethepushrodtravelisbarelywithintolerancewhenthebrakedrumsarecold?
5. Whatitemsshouldyoucarrytomeasureandadjustslackadjusters?
6. Whatisthefirstthingyoushoulddowhenpreparingtomeasureslackadjustment?
7. Howmuchpressureshouldyouapplytothefootvalvewhenmeasuringslackadjustmentusingtheappliedstrokemethod?
8. Howdoyouknowyouareturningtheadjustingboltinthecorrectdirectionwhenadjustingaslackadjuster?
9. Whatisanadvantageofautomaticslackadjusters?
Air Brake Manual • 79
Pre–TripandPost–TripAirBrakeInspection
Section9
80 • Air Brake Manual
Vehicle InspectionAnairbrakeinspectionmustbecarriedoutoneveryairbrakeequippedvehiclebeforeyoustartdrivingitfortheday.
EverydriverofacommercialmotorvehiclemustcarryoutaninspectionandlogitasoutlinedinThe�Highway�Traffic�Actanditsregulations.Acommercialmotorvehicleis:
a. amotorvehiclewithaGVWRof4,500kgormorethatisapublicservicevehicleorcommercialtruck;
b. abuswithaseatingcapacityof11ormore,includingthedriver,thatisusedfortransportationofpersonsorpropertyonahighwayforgainorcompensation;or
c. aschoolbus.
Theinspectionwilltakeplacebeforethevehicle’sfirsttripoftheday,andifatriplastsmorethanoneday,beforethetripbeginsonthefirstday,andnolaterthanthefirstreststoponthesecondandeverysubsequentday.
Regardlessofthemaintenancepoliciesofcompaniesofvehicleowners,alldriversmustbecapableofdeterminingiftheirvehicleisinsafeoperatingconditionasoutlinedinThe�Highway�Traffic�ActanditsRegulations.
Apersonwhocarriesoutavehiclepre–tripinspectionmustmakeatripinspectionreportinlegiblewritingthatcontainsthefollowing:
1. Thelicenceplatenumberorunitnumberofthevehicleandanytrailertowedbyit.
2. Thedateofinspection.
3. Alistofanysafetydefects.
4. Ifnoitemsaredefectiveorrequiredtobereportedonthevehicleoranytrailertowedbyit,astatementtothateffect.
5. Thenameandsignatureofthepersonwhocarriedouttheinspection.
Ifadriverbelievesorsuspectsthatthereisasafetydefecttheymustreportthatbelieforsuspiciontothecarrier.Ifthedefectposesanunreasonableriskitmustbereportedimmediately.Anyothercasemustbereportedinatimelymanner.
Everycommercialvehicledrivermusthaveacurrenttripinspectionreportintheirpossessionforthevehicle?
Checkingavehiclebeforestartingout,asrequiredbylaw,willoftenpreventcostlydelaysaswellasreducethechancesofanaccidentresultingfromamechanicalfailure.
Air Brake Practical TestWhenupgradingyourdriver’slicencefromsingletocombinationvehicleswithairbrakes,youwillberequiredtosatisfactorilydemonstratethecompletepre–tripairbrakeinspectionforcombinationvehicles.
Thepre–tripairbrakeinspectionforcombinationunitsshouldbecompletedwithin30minutesand20minutesforsingleunits.Failuretocompletethetestwithintheabovetimelimitmayresultinthetestbeingdiscontinued.
Theairreservoirsmustbedrainedorfanneddowntozeropressurepriortothepre–tripinspectiontosimulatethattheyweredrainedduringtheposttripinspection.
Youarerequiredtobringallmaterial/toolstocompletetheairbraketest(i.e.wrench,chalk,watch,etc.)Itisrecommendedthatyouwearsafetyglassesandabumpcapwhenperformingapre–tripinspection.
Practicalexaminationwillbeconductedineitherthemetricorimperialsystemsofmeasurement,whichevercoincideswiththeequipmentbeingoperated.
Air Brake Manual • 81
Pre–Trip Inspection—Combination UnitTheairbrakepre–tripinspectionwhenperformedcorrectlywillidentifyanymalfunctioningcomponentsorproblemswiththesystem.Failuretocompleteathoroughpre–tripinspectionoftheairbrakesystemcouldresultinavehiclebeingoperatedonthehighwaywithafaultybrakesystem,whichcouldpotentiallybedeadly.Completingathroughpre–tripinspectionwillallowthedrivertooperatethevehiclewithreducedchanceofbreakdownorsystemmalfunction.Itisthedriver’sresponsibilitytoensuretheairbrakesystemissafeandfunctioningproperlybeforemovingthevehicle.
Vehicle Secure
A.1 Ensureparkingbrakeisapplied(trailersupplyvalveandtractorspringparkingbrakecontrolvalveareclosed),wheelsareblockedandparkedonlevelground.
A.2 Checkreservoirairpressureisat0psiandthecompressorissecure,nooilorcoolantleaksanddrivebeltsforwearandtension.
A.3 Visuallyinspectallbrakesystemairhoses,gladhands,chambers,pushrods,slackadjusters,drumsfordamageandaremountedproperlyandsecure.
Compressor and Warning Devices Check
A.4 Starttheengineandcheckthatthegaugesarefunctioningproperlyandlowairpressurewarningdevicesareoperating.
A.5 Buildairpressureathighidle,ensurereservoirairpressurebuildsfrom50to90psiwithinthreeminutes.
A.6 Lowairpressurewarningdevicesmustoperatetoaminimumof60psi.
A.7 At90psiorabove,openthetractorspringparkingbrakecontrolvalveandthetrailersupplyvalve,releasingthespringparkingbrakes.Applyandreleasethetrailerservicebrakeswiththetrailerhandvalvewhilelisteningforairtoexhaustatthetrailer.Thiswillindicateifthebrakesarereleasingandthatthegladhandsarenotcrossed.
A.8 Continuebuildingairpressureandcheckthatthegovernorplacesthecompressorintheunloadingstagebetween115psiand135psi,(theairpressuregaugeswillstoprising).
A.9 Fantheservicebrakepedaluntiltheairpressuredropsto90psiandnolowerthan80psi.Stopfanningtoseeifthegovernorhasplacedthecompressorintheloadingstage(thereadingontheairpressuregaugeshouldincrease).
A.10 Continuefanningtheservicebrakepedal.Lowairpressurewarningdevicesmustoperateataminimumof60psiandthetrailersupplyvalvemustcloseataminimumof20psi.
Note: Tractor spring parking brake control may–or may not–also close.
Tractor and Trailer Emergency Systems Check
A.11 Ensurethetrailersupplyvalveandtractorspringparkingbrakecontrolvalveareclosed,applyingthespringparkingbrakes.Exitthecabanddisconnectthesupply(emergency)linegladhands.Noairshouldescapefromeitherofthegladhands.
82 • Air Brake Manual
A.12 Enterthecabandensurethereservoirairpressureisbetween115psito135psi,shut–offtheengine.Openthetrailersupplyvalve.Airlossfromdisconnectedgladhandwilleitherstopimmediatelyorbleeddowntonolowerthan20psiwhenthetrailersupplyvalveclosesandtheairlossstops.
A.13 Ensuretrailersupplyvalveandtractorspringparkingbrakecontrolvalveareclosed,applyingthespringparkingbrakes.Startenginetorebuildtofullreservoirairpressurebetween115psiand135psi.Exitthecabandre–connectthesupply(emergency)linegladhands.
Tractor Protection Valve Check
A.14 Enterthecabandatorabove90psi,openthetrailersupplyvalve.Exitthecabanddisconnectthecontrol(service)linegladhands.Noairshouldescapefromeitherofthegladhands.
A.15 Enterthecab,ensurefullreservoirairpressurebetween115psiand135psi,openthetractorspringparkingbrakecontrolvalve.Shutofftheengine.
A.16 Makeafullservicebrakeapplicationandholdit.Airshouldescapefromthecontrol(service)linetonolowerthan20psi,thetractorprotectionvalvewillcloseandtheairlosswillstop.Releasetheservicebrakeapplication.
A.17 Closethetractorspringparkingbrakecontrolvalveandensurethetrailersupplyvalveisclosed,ifnot,closeitmanually.Starttheengineandrebuildairpressure.Atorabove90psi,makeatrailerservicebrakeapplicationwithtrailerhandvalve.Noairshouldescapefromthedisconnectedcontrol(service)line.Releasethehandvalveapplication.
A.18 Exitthecabandre–connectthecontrol(service)linegladhands.
A.19 Enterthecabandatorabove90psi,openthetractorspringparkingbrakecontrolvalveandtrailersupplyvalve,continuebuildingairpressuretobetween115psito135psi.Onceatfullpressure,shutofftheengine.
Air Leak Check
A.20 Makeafullservicebrakeapplicationwiththefootvalveandholditforoneminute.Airpressuremustnotdropmorethan4psi.
A.21 Listenforaudibleairleaks.Releasetheservicebrakeapplication,starttheengineandrebuildtofullsystemairpressurebetween115psiand135psi.
Brake Adjustment—Combination UnitNote: For checking if your brakes are in adjustment you will require a second person to apply and hold the service brakes on or a device to apply and hold the service brakes on.
A.22 Ensurethetractorspringparkingbrakecontrolvalveandtrailersupplyvalveareopen.(Forvehiclesequippedwithautomaticslackadjusters, makeafullservicebrakeapplicationandrelease.Repeatthisprocess6times,ensurereservoirairpressureisabove90psiforeachfullbrakeapplication).
A.23 Ensurereservoirairpressureisabove90psi,shutofftheengine.(Foraddedsecurity,placemanualtransmissioninlowgear.)
Air Brake Manual • 83
Brake Adjustment Verification for Automatic or Manual Slack AdjustersForsafetyreasonsinspectthetractorortrailerbrakesseparately.Thiswillallowthespringparkingbraketobeappliedonthebrakesthatarenotbeinginspectedpreventingthevehiclefrommoving.Measurementsforslackadjustmentarefortype30standardstrokebrakechambers.
A.24 Exitthecabandmakeachalkmarkonthepushrodwhereitentersthebrakechamber.Repeatforallchambers.
A.25 Enterthecabandensurereservoirpressureisbetween90psiand100psi.Withabrakepedalassistingdeviceorasecondperson,makea90psito100psiservicebrakeapplicationandhold.
A.26 Returntothebrakechambersandmeasurethepushrodtravelbycheckingthedistancefromthechambertothechalkmarkonthepushrod.Ensurethepushrodtraveliscorrectforthesizeandtypeofbrakechamberbasedonmanufacturer’sspecifications.Also,brakechamberswhichsharethesameaxlemusthaveapushrodtravelmeasurementwithin1/$inchofeachother.
Note:For automatic slack adjusters, the slack adjuster must be replaced if measurements are not within the above specifications.
Adjustment for Manual Slack Adjusters OnlyFordriver’swith“S”airbrakeendorsement
M.1 Enterthecabandremovethebrakepedalassistingdevicereleasingtheservicebrakes.Ensurereservoirpressureisatorabove90psi.
M.2 Returntotheslackadjusterrequiringadjustmentandlocatetheadjustmentbolt.Withtheproperwrench,disengagetheadjustmentboltlockingmechanism.Turntheadjustmentboltuntilthebrakeliningcomesintocontactwiththebrakedrum.Ifthiscannotbeconfirmedbyvisuallyseeingtheliningandbrakedrumduetothedustcover,observethedirectionoftheS–camshaftwhileturningtheadjustmentbolt.TheS–camshaftshouldturninthesamedirectionasitwouldwhenabrakeapplicationisbeingmade.
M.3 Aftertighteningtheadjustmentbolt,turntheadjustmentboltintheoppositedirection1/$toMaturn.Removethewrenchandensurethelockingdevicereturnstothe“locked”position.Failuretoengagethelockingdevicecouldresultintheadjustmentboltturningandcausingthebraketobecomeoutofadjustmentwiththeapplicationofthebrakes.Completethesestepsforallslackadjusters.
M.4 Enterthecab;ensurereservoirairpressureisabove90psiandmakea90psito100psiservicebrakeapplicationandhold.Useabrakepedalassistingdeviceorasecondpersontoholdtheapplication.
M.5 Returntothebrakechambersandmeasurethepushrodtraveltoensuretraveliswithin1Minchesorwithinmanufacturer’sspecifications.Alsobrakeswhichsharethesameaxlemusthaveapushrodtravelmeasurementwithin1/$inchofeachother.
Note: If one slack adjuster requires adjustment then all slack adjusters must be adjusted.
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Brake Response Tests
A.27 Ensurethetractorandtrailerspringparkingbrakesareappliedandremovethewheelblocks.
A.28 Enterthecabandstarttheengine.Openthetractorspringparkingbrakecontrolvalveandplacethevehicleinalowforwardgear.Gentlytugagainsttheappliedtrailerspringparkingbrakes.Theymustholdthevehicle.
A.29 Closethetractorspringparkingbrakecontrolvalveandopenthetrailersupplyvalve.Gentlytugagainsttheappliedtractorspringparkingbrakes.Theymustholdthevehicle.
A.30 Openthetractorspringparkingbrakecontrolvalveandapplythetrailerservicebrakesusingthetrailerhandvalve.Gentlytugagainstthetrailerservicebrakes.Theymustholdthevehicle.
A.31 Releasethetrailerservicebrakeapplication,movethevehicleaheadslowlyandmakeaservicebrakeapplicationwiththefootvalvetocheckbrakeresponse.
Post–Trip Inspection—Combination UnitAttheendofthefinaltripofthedayyoumustinspectyourvehicleforanydamageofproblemsthatmayhavedevelopedontheroadandcompleteatripinspectionreport.Thisreportmustnoteanydefectsfoundduringthepost–tripinspection.Thepost–tripinspectioncanbeaddedtothereportyoucompletedduringthepre–tripinspectionatthestartofthatday.
Theairbrakesystempost–tripinspectionshouldincludethefollowing:
• Parkthevehicleonlevelground,applythespringparkingbrakes,shutofftheengineandleaveitingear.
• Visuallyinspectallbrakesystemairhoses,chambers,pushrods,slackadjusters,drumsfordamageandaremountedproperlyandsecure.
• Openthedrainvalvesonallairreservoirsandallowallairpressuretoescapethenclosethedrainvalves.
Air Brake Manual • 85
Pre–Trip Inspection—Single Unit(Not for air–over–hydraulic brake systems.)
Theairbrakepre–tripinspectionwhenperformedcorrectlywillidentifyanymalfunctioningcomponentsorproblemswiththesystem.Failuretocompleteathoroughpre–tripinspectionoftheairbrakesystemcouldresultinavehiclebeingoperatedonthehighwaywithafaultybrakesystem,whichcouldpotentiallybedeadly.Completingathroughpre–tripinspectionwillallowthedrivertooperatethevehiclewithreducedchanceofbreakdownorsystemmalfunction.Itisthedriver’sresponsibilitytoensuretheairbrakesystemissafeandfunctioningproperlybeforemovingthevehicle.
Vehicle Secure
B.1 Ensurethespringparkingbrakecontrolvalveisclosedapplyingthespringparkingbrakes,wheelsareblockedandparkedonlevelground.
B.2 Checkreservoirairpressureisat0psiandthecompressorissecure,nooilorcoolantleaksanddrivebeltsforwearandtension.
B.3 Visuallyinspectallbrakesystemairhoses,chambers,pushrods,slackadjusters,drumsfordamageandaremountedproperlyandsecure.
Compressor and Warning Devices Check
B.4 Starttheengineandobservethegaugesarefunctioningproperlyandlowairpressurewarningdevicesareoperating.
B.5 Buildairpressureathighidle,ensurereservoirairpressurebuildsfrom50to90psiwithinthreeminutes.
B.6 Lowairpressurewarningdevicesmustoperatetoaminimumof60psi.
B.7 Continuebuildingairpressureandcheckthatthegovernorplacesthecompressorintheunloadingstagebetween115psiand135psi.(theairpressuregaugeswillstoprising.)Openthespringparkingbrakecontrolvalve,releasingthespringparkingbrakes.
B.8 Fantheservicebrakepedaluntiltheairpressuredropsto90psiandnolowerthan80psi.Stopfanningtoseeifthegovernorhasplacedthecompressorintheloadingstage(thereadingontheairpressuregaugeshouldincrease.)
B.9 Continuefanningtheservicebrakepedal.Lowairpressurewarningdevicesmustoperateataminimumof60psi.Buildreservoirairpressureatfastidletofullairpressurebetween115psiand135psi.
B.10 Ensurethespringparkingbrakesarereleasedbyopeningthespringparkingbrakecontrolvalveandthenshutofftheengine.
Air Leak Check
B.11 Makeafullservicebrakeapplicationwiththefootvalveandholditforoneminute.Airpressuremustnotdropmorethan3psi.
B.12 Listenforaudibleairleaks.Releasetheservicebrakeapplication,starttheengineandrebuildtofullsystemairpressurebetween115psiand135psi.
86 • Air Brake Manual
Brake Adjustment—Single Unit
(Buseswithlowgroundclearancemustbeadjustedbyaqualifiedmechanic)
Fortestingpurposes,applicantsoperatingbuseswithlowgroundclearancewillnotbeallowedtomanuallyadjustedthebrakesonthebus.
Note: For checking if your brakes are in adjustment you will require a second person to apply and hold the service brakes on or a device to apply and hold the service brakes on. Measurements for slack adjustment are for type 30 standard stroke brake chambers.
B.13 Ensurethespringparkingbrakecontrolvalveisopen.(Forvehiclesequippedwithautomaticslackadjusters,makeafullbrakeapplicationandrelease.Repeatthisprocess6times,ensurereservoirairpressureisabove90psiforeachfullbrakeapplication).
B.14 Ensurereservoirairpressureisabove90psiandshutofftheengine.(Foraddedsecurity,placemanualtransmissioninlowgear.)
Brake Adjustment Verification for Automatic or Manual Slack Adjusters
B.15 Exitthecabandmakeachalkmarkonthepushrodwhereitentersthebrakechamber.Repeatforallchambers.
B.16 Enterthecabandensurereservoirpressureisbetween90psiand100psi.Withabrakepedalassistingdeviceorasecondperson,makea90to100psiservicebrakeapplicationandhold.
B.17 Returntothebrakechambersandmeasurethepushrodtravelbycheckingthedistancefromthechambertothechalkmarkonthepushrod.Ensurethepushrodtraveliswithintwoinchesforautomaticslackadjusters,andwithin1Minchesformanualslackadjustersorwithinmanufacturer’sspecifications.Also,brakechamberswhichsharethesameaxlemusthaveapushrodtravelmeasurementwithin1/$inchofeachother.
Note: For automatic slack adjusters, the slack adjuster must be replaced if measurements are not within the above specifications.
Air Brake Manual • 87
Adjustment for Manual Slack Adjusters OnlyFordriver’swith“S”brakeendorsement
M.1 Enterthecabandremovethebrakepedalassistingdevicereleasingtheservicebrakes.Ensurereservoirpressureisatorabove90psi.
M.2 Returntotheslackadjustersrequiringadjustmentandlocatetheadjustmentbolt.Withtheproperwrench,disengagetheadjustmentboltlockingmechanism.Turntheadjustmentboltuntilthebrakeliningcomesintocontactwiththebrakedrum.Ifthiscannotbeconfirmedbyvisuallyseeingtheliningandbrakedrumduetothedustcover,observethedirectionoftheS–camshaftwhileturningtheadjustmentbolt.TheS–camshaftshouldturninthesamedirectionasitwouldwhenabrakeapplicationisbeingmade.
M.3 Aftertighteningtheadjustmentbolt,turntheadjustmentboltintheoppositedirection1/$toMaturn.Removethewrenchandensurethelockingdevicereturnstothe“locked”position.Failuretoengagethelockingdevicecouldresultintheadjustmentboltturningandcausingthebraketobecomeoutofadjustmentwiththeapplicationofthebrakes.Completethesestepsforallslackadjusters.
M.4 Enterthecab;ensurereservoirairpressureisabove90psiandmakea90psito100psiservicebrakeapplicationandhold.Useabrakepedalassistingdeviceorasecondpersontoholdtheapplication.
M.5 Returntothebrakechambersandmeasurethepushrodtraveltoensuretraveliswithin1Minchesorwithinmanufacturer’sspecifications.Also,brakeswhichsharethesameaxlemusthaveapushrodtravelmeasurementwithinNinchofeachother.
Note: If one slack adjuster requires adjustment then all slack adjusters must be adjusted.
Brake Response Test
B.18 Ensurethespringparkingbrakesareappliedandremovethewheelblocks.
B.19 Enterthecabandstarttheengine.Withthespringparkingbrakecontrolvalveclosed.Placethevehicleinalowforwardgear.Gentlytugagainstthespringparkingbrakes.Theymustholdthevehicle.
B.20 Openthespringparkingbrakecontrolvalve,movethevehicleaheadslowlyandmakeaservicebrakeapplicationwiththefootvalvetocheckbrakeresponse.
Post–Trip Inspection—Single UnitAttheendofthefinaltripofthedayyoumustinspectyourvehicleforanydamageofproblemsthatmayhavedevelopedontheroadandcompleteatripinspectionreport.Thisreportmustnoteanydefectsfoundduringthepost–tripinspection.Thepost–tripinspectioncanbeaddedtothereportyoucompletedduringthepre–tripinspectionatthestartofthatday.
Theairbrakesystempost–tripinspectionshouldincludethefollowing:
• Parkthevehicleonlevelground,applythespringparkingbrakes,shutofftheengineandleaveitingear.
• Visuallyinspectallbrakesystemairhoses,chambers,pushrods,slackadjusters,drumsfordamageandaremountedproperlyandsecure.
• Openthedrainvalvesonallairreservoirsandallowallairpressuretoescapethenclosethedrainvalves.
88 • Air Brake Manual
Pre–Trip Inspection—Air–Over–Hydraulic (Air Actuated) Brake SystemTheair–over–hydraulicpre–tripinspectionwhenperformedcorrectlywillidentifyanymalfunctioningcomponentsorproblemswiththesystem.Failuretocompleteathoroughpre–tripinspectionoftheairbrakesystemcouldresultinavehiclebeingoperatedonthehighwaywithafaultybrakesystem,whichcouldpotentiallybedeadly.Completingathoroughpre–tripinspectionwillallowthedrivertooperatethevehiclewithreducedchanceofbreakdownorsystemmalfunction.Itisthedriver’sresponsibilitytoensurethebrakesystemissafeandfunctioningproperlybeforemovingthevehicle.
Vehicle Secure
D.1 Ensuretheparkingbrakeisapplied,thewheelsareblockedandparkedonlevelground.
D.2 Checkreservoirpressureisat0psi(0kPa),thecompressorissecureandithasnooilorcoolantleaksandcheckthecompressordrivebeltsforwearandtension.Checkthehydraulicfluidreservoirlevelandthatthereisnohydraulicfluidleaks.
D.3 Visuallyinspectallwheelcylindersandlinesforhydraulicfluidleaks,drumsfordamage.
Compressor and Warning Devices Check
D.4 Starttheengineandcheckthatthegaugesarefunctioningproperlyandlowairpressurewarningdevicesareoperating.
D.5 Buildairpressureathighidle,ensurereservoirairpressurebuildsfrom50psi(344kPa)to90psi(621kPa)withinthreeminutes.
D.6 Lowairpressurewarningdevicesmustoperatetoaminimumof60psi(414kPa).
D.7 Continuebuildingairpressureandcheckthatthegovernorplacesthecompressorintheunloadingstagebetween115psi(793kPa)and135psi(931kPa).(theairpressuregaugewillstoprising).Openthespringparkingbrakecontrolvalve,releasingthespringparkingbrakes(ifequipped).
D.8 Fantheservicebrakepedaluntilthepressuredropsto90psi(621kPa)andnolowerthan80psi(552kPa).Stopfanningtoseeifthegovernorhasplacedthecompressorintheloadingstage(thereadingontheairpressuregaugeshouldincrease.)
D.9 Continuefanningtheservicebrakepedal.Lowairpressurewarningdevicesmustoperateataminimumof60psi(414kPa).Buildreservoirairpressureatfastidletofullpressurebetween115psi(793kPa)and135psi(931kPa).
D.10 Releasethespringparkingbrakesifequipped.Shutofftheengine.
Air Leak Check
D.11 Makeafullservicebrakeapplicationwiththefootvalveandholditforoneminute.Airpressuremustnotdropmorethat3psi(21kPa).
D.12 Listenforaudibleairleaks.Releasetheservicebrakeapplication,starttheengineandrebuildtofullsystempressurebetween115psi(793kPa)and135psi(931kPa).
Brake Response Test
D.13 Ensuretheparkingbrakeisappliedandremovethewheelblocks.
D.14 Applytheparkingbrakeandplacethevehicleinalowforwardgearandgentlytugagainsttheparkingbrake.Itmustholdthevehicle.
D.15 Releasetheparkingbrake,movethevehicleaheadslowlyandmakeaservicebrakeapplicationwiththefootvalvetocheckbrakeresponse.
Air Brake Manual • 89
Metric Conversion TableAconversiontothemetricsystemtookplaceinCanadaonSeptember1,1977,andsomecommonlyusedconversionsarelistedbelow.Numbershavebeenroundedandthereforearenotpreciseequivalents.
kPa to psi
5 0.72
10 1.45
15 2.17
20 2.90
25 3.62
30 4.35
35 5.07
40 5.80
45 6.52
50 7.25
60 8.70
70 10.15
80 11.60
90 13.05
100 14.50
150 21.75
200 29.00
250 36.29
300 43.51
310 44.96
350 50.76
400 58.01
415 60.19
450 65.26
500 72.51
550 79.77
585 84.84
600 87.02
650 94.27
700 101.52
725 105.15
750 108.77
800 116.03
850 123.28
900 130.53
950 137.78
1000 145.03
1050 152.29
psi to kPa
1 6.89
2 13.78
3 20.68
4 27.57
5 34.47
6 41.36
7 48.26
8 55.15
9 62.05
10 68.94
15 103.42
20 137.89
25 172.36
30 206.84
35 241.31
40 275.78
45 310.26
50 344.73
55 379.20
60 413.68
65 448.15
70 482.62
75 517.10
80 551.57
85 586.04
90 620.52
95 654.99
100 689.47
105 723.94
110 758.41
115 792.89
120 827.36
125 861.83
130 896.31
135 930.78
140 965.25
145 999.73
150 1034.20
Post–Trip Inspection—Air–Over–Hydraulic (Air Actuated) Brake System Attheendofthefinaltripofthedayyoumustinspectyourvehicleforanydamageorproblemsthatmayhavedevelopedontheroadandcompleteatripinspectionreport.Thisreportmustnoteanydefectsfoundduringthepost–tripinspection.Thepost–tripinspectioncanbeaddedtothereportyoucompletedduringthepre–tripinspectionatthestartofthatday.
Theair–over–hydraulicbrakesystempost–tripinspectionshouldincludethefollowing
• Parkthevehicleonlevelground,applythespringparkingbrakes,shutofftheengineandleaveitingear.
• Openthedrainvalvesonallairreservoirs,allowallairpressuretoescapeandthendrainvalves.
Section Summary Questions
1. Whatisthemaximumtimepermittedforthecompressortobuildfrom50to90psi?
2. Whatisthemaximumairpressurelosspermittedonafullbrakeapplicationwiththemotorshutoffforcombinationandsingleunits?
3. Howcantheholdingpowerofthetrailerbrakesbetested?
4. Whatisthefinalbraketestthatshouldbemadebeforethevehicleisputintoservice?
5. IsabrakeadjustmentpartoftheairbraketestgivenbyManitobaPublicInsurance?
90 • Air Brake Manual
Metric Conversion Table
1 inch = 2.54 cm
1 foot = 30.48 cm
1 mile = 1.61 km
Length
Volume
1 pint = 0.57 l
1 quart = 1.13 l
1 gallon = 4.55 l
Speed
1 mph = 1.61 km/h
10 mph = 15 km/h
15 mph = 25 km/h
20 mph = 30 km/h
30 mph = 50 km/h
40 mph = 60 km/h
50 mph = 80 km/h
60 mph = 100 km/h
8’ 6” = 2.60 m
10’ = 3.00 m
12’ 6” = 3.80 m
13’ 6” = 4.15 m
14’ = 4.20 m
35’ = 11.00 m
38’ = 11.50 m
40’ = 12.50 m
45’ = 14.00 m
60’ = 18.50 m
65’ = 20.00 m
100’ = 30.00 m
500’ = 150.00 m
Converted Linear Measurements
Converted Weight
10,000 lbs = 4 500 kg
12,000 lbs = 5 500 kg
20,000 lbs = 9 100 kg
24,000 lbs = 11 000 kg
Abbreviations
mm = millimetre
cm = centimetre
l = litre
km/h = kilometre per hour
m = metre
kg = kilogram
kPa = kilopascal
Air Brake Manual • 91
Pre-trip Inspection Tear Out SheetYou may use this sheet for your test. Do not add to, or write on this form. If altered it cannot be used on the test. The Air Brake Manual has specific inspection information that must be studied prior to the test.
Key points:• You need to perform the steps required for the
inspection of various air brake components and tell the examiner what you’re checking for. Never assume the examiner has enough information and delete items. When the examiner is satisfied in your knowledge of the area you may be asked to move along.
• The pre-trip inspection should be done in a systematic manner to conserve time. The air brake pre-trip inspection should take no more than 30 minutes to complete.
Inspection PointsVehicle Secure
• Check all air brake components outside
Compressor and Warning Devices Check
• Confirm zero air pressure
• Pressure build up
• Fan down air pressure
Tractor and Trailer Emergency Systems Check
• Disconnect the supply (emergency) line
Tractor Protection Value Check
• Disconnect the control (service) line
Air Leak Check
Brake Adjustment Verification
Adjustment for Manual Slack Adjusters Only (if Needed)
Brake Response Tests
✄
92 • Air Brake Manual
Air Brake Manual • 93
Organ and Tissue DonationEvery year in Canada, thousands of people are waiting for organ and tissue transplants. You can make the diff erence in the lives of many people by deciding to become a donor. Everyone has the potential to be an organ and tissue donor. The health of the donor, not the age, is the most important thing considered. Generally, organ donors are healthy people who have suff ered an irreversible brain injury, as in a motor vehicle accident or a brain hemorrhage. Organs and tissues that can be donated include: kidneys, heart, lungs, liver, pancreas, small bowel, corneas, solid bones and joints, skin and heart valves.
Sign a Donor Card Today and Discuss Your Wishes with Your Family!Signing a donor card is one way to indicate your wishes to be an organ and tissue donor. However, donor cards are often not available at the time of the donor’s death. Therefore, it is important that you discuss your wishes with your family. Other people you may want to inform of this wish are your clergy and family doctor. A Living Will is another place where you can record your wishes. If you have named a proxy in your Living Will, the proxy has precedence over the legal next-of-kin to give consent for organ and tissue donation if you have discussed your wishes with your proxy.
Drivers under the age of 18 years require the signature of a parent or guardian. Simply cut out the card on the following page, complete the information, and keep it with your Manitoba Health Registration Certifi cate or Driver’s Licence so it’s visible for law enforcement and hospital offi cials. Your donor card is a legal document that allows you to give any or all tissues and organs after death.
For further information and extra donor cards, contact:
Transplant Manitoba – Gift of Life Programwww.transplantmanitoba.ca204-787-1897
Tissue Bank Manitoba204-940-1750
The Lions Eye Bank of Manitoba and Northwest Ontario Inc.204-788-8419
DONOR CARDDirection under The Human Tissue Gift Act The Human Tissue Gift Act T C.C.S.M. c. H180
I,
direct the use, after my death (please check ✓) of:❑ any needed organs or parts of my body; or❑ the following specified organs or parts of my body, namely:
for the following purposes:❑ transplant and other therapeutic purposes;❑ medical education; ❑ scientific research.
Donor Signature Date
Co-signature of parent or guardian Date where donor is under 18 years of age.
94 • Air Brake Manual
If you wish to donate organ(s) or tissue after death, complete theattached donor card and KEEP IT WITH YOUR MANITOBA HEALTHREGISTRATION CERTIFICATE OR DRIVER’S LICENCE SO IT IS VISIBLEFOR LAW ENFORCEMENT AND HOSPITAL OFFICIALS.
IT IS EXTREMELY IMPORTANT TO DISCUSS YOUR DECISION WITHYOUR FAMILY TO ENSURE YOUR WISHES ARE FULFILLED.YOUR FAMILY TO ENSURE YOUR WISHES ARE FULFILLED.Y
For more information on organ and tissue donation, please contact one of the Human Tissue Gift Agencies listed below:
Transplant Manitoba-Gift of Life Program 204-787-1897
Tissue Bank Manitoba 204-940-1750
Lions Eye Bank of Manitoba and Northwest Ontario Inc. 204-788-8419
(R-09/09)
ORGAN AND TISSUE DONATION
$10.00DVL0025/0337–16–B3 (R–2010)
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