Compressed Air Installation Guide

A Guide toCompressed Air Installation

Presented byThomas Wright / Thorite Group

total compressed air solutions

SSo often nowadays the sale of industrialequipment is treated as a box movingexercise similar to domestic appliances where,say, if one needs a washing machine one knows it willdo the household wash perfectly well whatever itsmake, colour or style, without having to consider thetechnical aspects.The danger, however, in purchasing industrial plantthis way is that what seemed a bargain at the time ofpurchase turns out to be a costly nightmare in operationbecause technical factors relating to the particular dutyrequired were not studied beforehand.We at the Thorite/Thomas Wright Group have alwaysprided ourselves on our knowledge of the industry werepresent, which gives us the ability to advise ourcustomers on the correct equipment to match theirparticular requirements. Now we have put pen to paper

to produce this guide, so that you can have referenceto hand on the various factors involved in selectingthe correct compressor plant to match your particularrequirements.At the end of the guide we have an example of how toput the information contained to a practical use.We trust you will find it informative and helpful as areference to use as and when your need arises.ABBREVIATIONS USEDLitres/Minute (L/M).Litres/second (L/s).Cubic Feet/Minute (CFM)Pneumatic control equipment manufacturers use cubicdecimetres (dm3). Dont be confused, a cubicdecimetre is equivalent to a Litre.

This guide is printed and published by Thomas Wright / Thorite Group Ltd. We extend our grateful thanks to ARO,Hiross, HPC, Hydrovane and Norgren Martonair for material utilised in this publication. Special thanks are due to

T. R. (Tom) Taylor for his work compiling this publication from articles featured in Thorite Pneus. Thomas Wright/Thorite 1991. This Edition 2002 All rights reserved.

ContentsTYPES AND SELECTION .................................................................. 4 - 6AFTERCOOLING ............................................................................... 7 - 8CONDENSATE SEPARATION AND DRAINAGE ............................... 9 - 10REFRIGERATION DRYERS ........................................................... 11 - 12DELIQUESCENT AND DESICCANT DRYERS ................................ 13 - 14FILTRATION ........................................................................................ 15INSTALLATION............................................................................. 16 - 17ASSESSMENT OF COMPRESSOR PLANT ........................................... 18EXAMPLE ............................................................................................ 19PRESSURE SYSTEMS REGULATIONS ................................................ 21

Contents

Easy approx. conversion for Litres/second to cubic feet/minute. L/s x 2 + 10% or for greater accuracy L/s x 2 + 6%. 1 Bar equals 14.7 pounds/sq. inch.4

ComprComprComprComprCompressoressoressoressoressorsssssTYPES AND SELECTION

The ultimate aim whenpurchasing an aircompressor is toacquire an adequate supply ofcompressed air at the lowestcost consistent with reliableservice. As with all other formsof power transmission theinstallation of a compressed airsystem calls for capitalinvestment with consequentoperating and maintenancecosts and, therefore, theinformation on which selectionof plant is made should be asaccurate as possible.

Lowest initial capitalexpenditure does notnecessarily mean the bestinvestment bargain.

The factors to be considered are dealtwith below However, before detailingthese it may be helpful to mention thetypes of compressors available. Aircompressors fall into two generalcategories i.e. positive displacementand dynamic.

POSITIVEDISPLACEMENTThese compressors inhale air into avariable chamber which as it is reducedin size compresses the contained air anddischarges it at a higher pressure.Types of positive displacementcompressor:

a) Reciprocating compressors. Thecompressing element, either a piston ordiaphragm, has a reciprocating motioninside a cylindrical housing.

b) Helical and spiral lobe (screw)compressors have 2 rotary intermeshingrotors of helical form which displaceand compress the air. They have highrotational speed and air discharged isfree of pulsations.

c) Sliding vane compressors are rotaryunits in which axial vanes slide radiallyin a rotor which is revolving in aneccentric cylindrical housing.Discharged air is free of pulsations.

d) Two-impeller straight-lobedcompressors and blowers have twostraight mating but non-touching lobeswhich carry the air from intake port todischarge port. These are normally usedfor high flow/low pressure applications.

DYNAMICCOMPRESSORSThese are rotary continuous flowmachines in which a rapidly rotatingelement accelerates the air passingthrough the element, converting thevelocity head into pressure, partially inthe rotating element and partially instationary diffusers or blades.Types of dynamic compressor:

a) Centrifugal compressors -acceleration of the air is obtainedthrough the action of one or morerotating impellers, very high speed, freeof pulsation.

b) Axial compressors - acceleration ofthe air is obtained through the action ofa bladed rotor which is shrouded at theblade ends. Very high speed; highvolume.

The majority of compressors used in themanufacturing industry are positivedisplacement types, either recipro-cating, rotary vane or screw. Dynamiccompressors are used where very highvolumes of air are required.

THE BEST TYPEFOR THEAPPLICATIONThe first industrial use ofreciprocating compressors canbe traced back to 1860 and theyhave served industry very wellsince that date. However,despite their reliability and highefficiency (especially in thelarger sizes) they do poseproblems in respect of noise,vibration, installation costs and,due to the number of movingparts, overhaul when requiredcan be lengthy and expensive.The recent introduction of diecast aluminium components insmall reciprocatingcompressors, 0.37 to 7.5 kW

(0.5 to 10 H.P.), enables them to bemanufactured in large quantities at lowcost. This has opened up a very largemarket for D.I.Y. and small industrialusers. These units are very reliable andgive good monetary value.

Larger industrial users of compressedair now demand the low noise,reliability, ease of maintenance andinstallation offered by rotary vane andscrew type compressors and these nowhave the major share of this market.

SIZEThe sizing of compressor plant shouldideally be made on exact knowledge ofconsumption requirements of tools andaverage load factors. If this isunderestimated the compressor will betoo small and unable to maintain therequired pressure.

Conversely, if requirements are over-estimated there may be excessivecapital investment. However, it is saferto err on the high side, as in mostinstances the use of air will increase andtake up surplus capacity. Always bearin mind future expansion.

This may be hard to predict accuratelybut it should not be too difficult to planfor 3 years and if, after such time, thecompressor becomes overloaded itwould then be financially sound to

Easy approx. conversion for Litres/second to cubic feet/minute. L/s x 2 + 10% or for greater accuracy L/s x 2 + 6%. 1 Bar equals 14.7 pounds/sq. inch. 5

invest in additional or largercompressors.

Consideration should also be given toextra stand-by capacity by using two ormore compressors This would allowproduction to continue in the event offailure on one compressor and servicingof compressors can be carried out innormal working time. Where airdemand is variable it is also prudent tosatisfy demand by using a number ofcompressors running in tandem, whichcan be controlled automatically so thatonly the minimum amount of energy isused to meet the demand at any onetime. They can be set to cut ON andOFF in either sequential or cascadesequence.

OPERATING PRESSURE.The quantity of air delivered by acompressor is relative to its workingpressure. The higher the pressure thelower is the quantity delivered. It takes1 kW of energy to compress 2.83 L/S(6 CFM) to a pressure of 7 bar (100 psi).It is therefore wasteful to compress airto a higher pressure than the optimumworking pressure required. Most air-operated appliances work at 6 bar (88psi) pressure and it is usual to operatethe compressor at 7 bar (100 psi) toallow for regulation of the compressorand for transmission losses.

It is also wasteful to operate tools andappliances above their optimumworking pressure as it increases theconsumption without giving anyincrease in operating efficiency.

Where a specialised tool or applianceneeds a higher pressure than thatrequired for the rest of the factory it maybe more economical to fit a highpressure compressor to deal solely withthat particular requirement, especiallyif the volume required is small.

THE ENVIRONMENTCompressors should be sited in a clean,cool, well ventilated environment withample space around each unit to allowfor cooling and maintenance purposes.Where large compressors are requiredit is wise to provide lifting facilities, notonly for initial installation but also forfuture maintenance work to be carriedout efficiently.

Ventilation is important. Most small andmedium sized compressors are now aircooled, and adequate ventilation,although essential, is often overlooked.Frequently louvre openings are fitted tocompressor rooms to admit air, but noprovision is made to extract the heatedair. The result: there is no movement ofthe air and overheating occurs. A 4C

rise in ambient temperature will resultin a 1% increase in energy to achieveequivalent output from the compressor.

Local noise restriction and maximumpermissible noise level are furtherfactors to be considered; the rotary vaneand screw compressors are both muchquieter in operation than theirreciprocating contemporaries.

A CLEAN SYSTEM

SAVES MONEYThe two worst enemies of a compressedair system are water and the oil carriedover from the compressor. Poor qualityair reduces the efficiency of air operatedappliances and creates breakdownswhich result in lost production.Elimination of these two problems atsource, before the air is fed into thedistribution system, can pay largedividends.

ENERGYCONSERVATION.This is a topic often discussed yet so


High Temperature = Loss of efficiency

Water & oil In airlines = breakdown =lost production


often neglected. What then can one doin regard to a compressed air system tosave energy and stop ones hard earnedprofits going down the drain?

Regular preventative maintenance ofcompressor plant ensures maximumoperating efficiency. Correct sizing ofpipes, hoses and couplings and regularcleaning or renewal of filter elements,will all prevent pressure loss.

Earlier we mentioned that it takes 1 kWto produce 2.83L/s (6 CFM) at 7 bar(100 psi) so keep checking and

correcting leaks. The equivalent of a 3mm (1/8) dia. hole in a pipe containing7 bar (100 psi) will lose you 3.36 kW(5 H.P.) of electricity.

Considerable savings can be made byfitting a pressure regulator to each air-operated appliance so that only theminimum pressure required to giveoperational efficiency is supplied.

Use of pressures above the minimumwill increase consumption of theappliance without giving any increasein its efficiency.

CHECKLISTA summary of factors to consider when selecting compressor plant

1. Volume of air requiredCalculate total consumption of tools and appliances to be used, taking into consideration load factors, andadd 25% to allow for future expansion. If in doubt ask for assistance.

2. Working PressureUse minimum discharge pressure that will maintain acceptable working pressure at points of use. If just oneor two particular appliances require a higher pressure than the rest of the factory, consider a separate highpressure compressor for this purpose.

3. Load SplittingIn all installations thought should be given to having at least two compressors to allow for light loadperiods, energy saving and maintenance.

4. Site ConditionsMust be cool, clean, well ventilated. Lifting facilities, space for servicing. Noise level and local restrictionson noise, ambient conditions - temperature, humidity and cleanliness of air, electrical supply voltage, phasefrequency.

5. Quality of air requiredType of dryer to give required dewpoint. Type of oil removal filters to give required quality of air.

6. Initial Capital InvestmentLowest initial cost should not be the prime factor, as it may well prove to be the most expensive long term.Always take account of running, maintenance and repair costs and reliability.

7. ServicingAre spares and servicing facilities easily available.

The above table shows the volume of air(at 7 bar) lost through holes of variousdiameter, together with the resultantapproximate power required to maintainsuch leakage.

HEAT RECLAMATIONThe energy used by a compressor is allconverted into heat the majority ofwhich can be reclaimed. This ispotentially the most rewarding area forenergy savings and ideally should beconsidered when installing newcompressors.

It is advisable, therefore, to seek advicefrom specialists when selectingcompressor plant.



It is regrettable, but true, that asubstantial proportion of responsibleexecutives in small and medium sizedbusinesses consider that the quality ofcompressed air is a matter of secondaryimportance. They believe that the onlyfirms which need concern themselvesabout air quality are those which uselarge quantities of compressed air, thosemaking use of sophisticated pneumaticapplications. It is true that largecompanies go to considerable troublein this field but they do it for one reasonand one reason only. They know howmuch it will cost them if they dont.

The smaller compressed air user onlydiffers in that he can frequently get bywith poor quality air and is unaware ofthe extra running costs that it involves.These extra running costs of coursedirectly affect his profitability andcompetitiveness.

The truth of the matter, the undisputabletruth, is that every user requirescompressed air conditioning to a greateror lesser degree and responsibleexecutives, unless they really knowtheir subject, should always make apoint of obtaining expert advice on thesubject.

WATER VAPOURAtmospheric air always contains aconsiderable quantity of water vapour.The level of humidity may vary fromlocation to location and from day to day,but water is always there (indeed,without it we would die) and whateverwater vapour is in the atmosphere willbe sucked in with the air at thecompressor intake. When the air iscompressed to 7 bar gauge (100 psig),each cubic metre of air at the intake isreduced in volume to one eighth of acubic metre at the compressor dischargeport. If the compression were to takeplace at constant temperature thereduced volume of air would no longerbe able to retain all the water in vapourform and it would start to condense outas liquid water.

However, when air is compressed itstemperature also rises and the hotter the

air, the more water vapour it is able tocontain, even at the reduced volume.Condensation does not thereforeusually occur inside the compressor. Infact, manufacturers take stringentprecautions to try and ensure that it doesnot, because of the obviouslydetrimental effect liquid water wouldhave on the internal components of thecompressor.

The problem therefore comes if thecompressed air cools, which of courseit does, in the pipelines after thecompressor. As the air cools, waterbegins to condense out. The water thencauses problems of corrosion,equipment inefficiency or malfunctionand even (in the case of spray painting)product spoilage.

THE AFTERCOOLERAs much as 50 to 60% of the watervapour contained in the air can becondensed out by artificially cooling theair as soon as it leaves the compressor.This is the function of the aftercooler.Most of the new compressors, exceptthe smallest, offered today by ThomasWright/Thorite have their ownaftercooler built in, but there are still asurprisingly high number of existinginstallations without an efficientaftercooler.

In any case a knowledge of howaftercoolers work and their limitationsis important to an understanding of theoperation of other compressed airconditioning components.

There are two basic types of aftercooler:air- and water-cooled.

AIR COOLEDAFTERCOOLERSMost aftercoolers used in small systemsare air-cooled so that no cooling watersupply is required. The maincomponents of an air-cooled aftercoolerare the finned coil heat exchanger orradiator through which thecompressed air passes and a motor-driven fan which provides the ambientairstream across the coil.Clearly the compressed air can only becooled to a temperature somewhatabove the temperature of the ambientair used to cool it. This temperaturedifference is usually between 5 to 15Cdepending upon the size and type ofaftercooler, and how well it is matchedto the application.

In order to select the right aftercoolerfor an installation, four main parametersmust be considered:

- compressed air flow rate- compressed air temperature at the

inlet to the aftercooler

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- working pressure- the ambient conditions in the

vicinity of the compressor andaftercooler.

The lower the compressed airtemperature at the aftercooler outlet, thegreater will be the quantity of watercondensed out from the air. Here aretwo important tips in this respect:

1. Site the aftercooler where it hasaccess to the coollest possible ambientair and make sure that the location iswell ventilated

2. Brush out dirt and dust from betweenthe fins of the aftercooler regularly witha soft brush and clean the tinsthoroughly at least once a year.

Hiross air-cooled aftercoolers have acoil design incorporating copper tubeswith aluminium fins which make themparticularly efficient, compact andcorrosion resistant. Standard units useelectric motors to drive the cooling fanbut Hiross can also offer versions withair-driven motors when required.

WATER-COOLEDAFTERCOOLERS.For some applications a water-cooledaftercooler may be more appropriateand, in some circumstances, it may evenbe possible to recover heat from thecompressed air.

Thomas Wright/Thorite offer Hirosswater-cooled aftercoolers which are ofa shell-and-tube design. Thecompressed air flows through the tubesand is cooled by the water flowingacross the outside of the tubes withinthe shell.

The secret of the high efficiency andcompact dimensions of the Hirossaftercooler lies in the patented fininserts which are used inside the coppertubes.

In order to select the right water-cooledaftercooler for an installation, the sameparameters must be considered as foran air-cooled version, with additionalinformation on the temperature andquantity of cooling water available.

Depending upon the quality of thecooling water there may be a tendencyfor scale to form on the outside of thetubes in the aftercooler. Appropriatemeasures in terms of water treatmentand/or regular cleaning should be takenin order to prevent the build up of scaledeposits which would otherwise reducethe efficiency of the aftercooler.

CONDENSATESEPARATIONCausing water vapour to condense outof the compressed air is only part of thestory. The condensate actually forms asa very fine mist which is suspended inthe airstream and will still be carrieddownstream if some means is notemployed of physically separating itfrom the air.

Thomas Wright/Thorite Group areproud and active members of...

BFPDAand

BCASYour assurance of service.

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ComprComprComprComprCompressed air conditioningessed air conditioningessed air conditioningessed air conditioningessed air conditioningCONDENSATE SEPARATION AND DRAINAGE

In the previous section we examined theproblem of water vapour in air and howcompressed air can no longer retain allthe water in vapour form when itstemperature is reduced in an aftercoolerso that condensation occurs.

We looked at the different types ofaftercooler available, selection criteriaand gave some tips on getting the bestperformance from your aftercooler.

However, an aftercooler which issimply causing water vapour to con-dense out of the compressed air servesno useful purpose at all if the dropletsof water are not separated from theairstream and drained out of the system.

SEPARATIONWhen water condenses out ofcompressed air it does so as a very finemist of microscopic droplets which iscarried along in the airstream. Very fewdroplets are of sufficient weight simplyto fall out from the airstream and itrequires a change in direction of theairflow to start the process ofseparation.

A simple form of separator is shown inFigure A.

It consists of a small pressure vesselcontaining a baffle plate. The airentering the separator is forced tochange direction as it reaches the baffleplate in order to get past. The heavierwater droplets hit the baffle plate wherethey coalesce to form larger drops untilthe force of gravity is sufficient to causethem to run down the baffle and drip tothe bottom. The efficiency of this typeof separator can be increased by usinga larger number of baffles as shown infigure B.

One immediate drawback of anyseparator of this type is obvious: infalling to the bottom, the water dropletshave to traverse the airstream and someof the water is inevitably re-entrainedin the compressed air. This type ofseparator is also of limited effectivenessin separating the finer droplets of waterwhich tend to remain in the airstreamrather than stopping on the baffles.

CENTRIFUGALSEPARATORSA much more efficient way ofseparating condensate from theairstream is through the vortex actionof so-called centrifugal separation.Figure C illustrates how this approachworks. The air entering the separatorflows across the vortex generator whicheffectively spins the air around theinside of the vessel. This vortex actioncauses the water droplets to be flung tothe inside walls of the separator wherethey coalesce and run down to thebottom. It is important to note that thegreater proportion of finer droplets isalso separated in this way.

It will also be noticed that thecondensate that flows down the wallsof the vessel does not have to cross theairstream in reaching the bottom and therisk of reentrainment is practicallyeliminated. The location of a horizontalbaffle near the bottom of the separatorcreates a quiet zone to prevent the air

from stirring up the condensate at thebottom.

Hiross Condensate Separators offeredby Thomas Wright/Thorite are of thecentrifugal type. The ACS range coversflow rates up to 141L/s (300 cfm) andutilizes a cast aluminium construction,while for higher flow rates there are theNS models made from carbon steel.

A drawback with many separators isthat their efficiency can decreaserapidly at higher and lower flow ratesand pressures than the nominalconditions for which they are designed.

Computer-aided design techniques haveenabled Hiross to overcome thisproblem and guarantee a separationefficiency between 95 and 99% over awide range of operating conditions.

COMPRESSORPACKAGESMost rotary compressors today havebuilt-in aftercoolers and it is commonfor the manufacturer to rely on thedirectional changes in airflow withinthe aftercooler to cause separation ofthe condensate as shown in figure D.

This is not very efficient and anyinstallation incorporating such acompressor package would benefit fromfitting a proper centrifugal separator atthe outlet.

DOWNSTREAMSEPARATIONOf course it is not only in an aftercoolerthat moisture condenses out of thecompressed air. When the air leaves theaftercooler, even if all the liquid waterit contains is separated out, it is stillsaturated with water vapour. Since its


temperature is several degrees aboveambient, it will inevitably cool furtherin the distribution lines, causing moreof the water vapour to condense out.Further centrifugal separators shouldtherefore be installed near to the pointsof use of the air.

Ideally, though, a dryer should beinstalled in the first place immediatelydownstream of the aftercooler or airreceiver, thereby eliminating anyproblems of condensation in the system.

CONDENSATE DRAINAGEOnce the condensate has collected inthe bottom of the separator, or any otherlow point in the system for that matter,such as an air receiver or down-leg, itmust be drained regularly. Otherwisethe level will rise causing an excessivepressure drop and carry-over of waterdownstream.

A manual drain cock is not to berecommended in most cases because itwill not usually be operated regularlyor frequently enough. The answer is toinstall an automatic drain trap.

Automatic drain traps can be dividedinto two broad categories: electro-mechanical and mechanical.

ELECTROMECHANICALAUTODRAINSIn electromechanical autodrains thevalve is opened at preset intervals for apreset duration, either by means of atimer-operated solenoid or a motordriven cam.The advantage of this type of valve isthat being power operated it can have alarge bore valve seat and is thereforeusually good at handling quite viscousemulsions of condensate and oil.

However, it does need a power supplywhich can substantially increaseinstallation costs and may make it ratherinconvenient for downstream use. Sinceit operates on a time cycle and not whenmoisture has accumulated, it can eitherleave accumulated liquids in the systemor waste air, depending on the setting.

Some autodrains of this type allow foradjustment of the setting but since therate of moisture condensation can varyconsiderably over a day and over theyear the settings will always be acompromise.

MECHANICALAUTODRAINSNearly all mechanical autodrains use afloat valve in one form or another. Theimmediately obvious advantage of thistype is its simplicity of installation: itdoes not need a power supply. It alsoprevents wastage of air and accumu-lation of liquid because it maintains anearly constant liquid level. As thelevel, and therefore the float, rises, thevalve opens to discharge condensate,causing the level to fall and the valveto close again.The discharge orifice is smaller thanthat in electromechanical types becauseof the mechanical force needed to openthe valve. For this reason many floattraps cannot readily cope withcondensate that is contaminated with oiland dirt and are accordingly prone toblockage. This is especially true of draintraps designed for the comparativelyclean condensate encountered in steamsystems and such traps should never beused in a compressed air system.

A well designed float trap however,such as the Hiross SAC 120 (1/2") orSAC 100 (l"), can handle condensatewith the degree of contamination found

in most systems. Excessivecontamination though is a symptom ofa serious problem upstream and shouldbe tackled at source.

Another important feature to look forin a drain trap is a manual vent whichcan be operated periodically to flush thetrap and ensure that it is functioningcorrectly.

When an autodrain is first installed itis common for a lot of particles of dirt,rust, swarf etc. to find their way into itand it is therefore good practice todismantle and clean it once or twice inthe first few weeks of operation toprevent blockages.

Thereafter it may only need cleaningout once a year, depending upon thestate of the system.

Under certain circumstances anautomatic drain trap may fail to operatedue to a phenomenon known as airbinding. This occurs when the air inthe body of the trap is unable to passback into the system past thecondensate. This causes an increase inpressure in the trap to the point at whichthe condensate ceases flowing into it.The problem is solved by installing aninternal balance nipple or an externalpipe for pressure equalisation.

As always, it is worth seeking the kindof expert advice which can be providedby specialists such as Thomas Wright /Thorite Group.

AIR DRYINGThe single most important step that themajority of compressed air users cantake to improve the overall efficiencyof their systems is the installation of adryer. Why this should be so is dealtwith in the next section.

For Compressed Air TreatmentcontactCompressed Air Specialists

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There is a popular misconception thatthe compressed air leaving anaftercooler is dry. Whilst it is true thatan efficient aftercooler and separatormay remove up to 60% of the watervapour contained in the air, there aretwo very important reasons why itcannot, by any stretch of theimagination, be considered dry:

1. the air leaving the aftercooler is 100%saturated so that any furthertemperature reduction will inevitablycause more water to condense out.

2. the temperature of the air leaving theaftercooler is likely to be between 25and 35C and certainly above thesurrounding ambient temperature.

The temperature of the compressed airwill therefore fall as it flows throughthe distribution system, causing furthercondensation inside pipes, tools,instruments and other air-operatedequipment.

To take care of this difficulty, and allthe extra running costs it causes, a dryeris needed to provide compressed airwith the right dewpoint.

DEWPOINTWhat is dewpoint? The quantity ofwater vapour which air can holddepends upon its temperature and itspressure. If air is cooled at a constantpressure it will eventually reach atemperature at which it becomessaturated and any further reduction intemperature will cause moisture tocondense as a liquid (as it does in anaftercooler). This saturationtemperature is therefore a measure ofthe water vapour contained in the airand is referred to as its dewpoint.

REFRIGERATION DRYINGAn obvious means of reducing thedewpoint of the air is by artificiallycooling the air down to a lowtemperature before it passes into thedistribution system. This is exactly whata refrigeration type dryer does.Refrigeration dryers normally cool thecompressed air down to a temperaturea little above freezing point, about 2

to 3C because below this thecondensate could freeze and block thesystem. The condensed water that thiscooling produces is separated anddrained so that the air leaving the dryerhas a dewpoint of 3C.

In the vast majority of industrialapplications, the air temperature withinthe distribution lines is never likely todrop below this value; accordingly, nofurther condensation will occur and thewhole system will stay dry. In fact mostrefrigeration dryers, except the smallest,also employ an air-to-air heat exchangerwhere the cold dry outgoing air pre-cools the warm saturated air enteringthe dryer. Provided that the condensedwater has been effectively separatedfrom the air in the dryer, reheating doesnot affect the dewpoint of thecompressed air which remains at 3C.

Employing the air-to-air heat exchangerreduces the amount of refrigeration cap-acity required and hence also reducesthe energy consumption of the dryer.

Refrigeration dryers fall into twocategories; thermal mass and directexpansion. The difference between thetwo types of refrigeration dryer is in theapplication of the cooling effect.

i) Thermal mass refrigeration dryer

A conventional refrigeration circuit isused to reduce the temperature of avessel containing a thermal mass (e.g.a water/antifreeze mixture, brine,

aluminium granules, etc.) toapproximately 0C.

Compressed air is then cooled bypassing it through a coil immersed inthe thermal mass in order to achieve thedesign pressure dewpoint. Within thethermal mass, the condensed watervapour is separated from the air streamand rejected to drain.

Obviously, in order to give the correctpressure dewpoint, the dryer mustalways maintain the thermal mass at thecorrect temperature so this type of dryermust always be switched on some timebefore the air compressor is started, inorder to bring the thermal mass downto the operating temperature.

Thermal mass dryers may or may notbe fitted with an air-to-air heatexchanger.

ii) Direct expansion refrigeration dryer

This type of dryer employs the simplestmost positive method of dryingcompressed air: by cooling it via directheat exchange with refrigerant.

A direct expansion dryer usuallyemploys two heat exchangers which canbe either separate vessels orencapsulated in one module. Saturatedair enters an air-to-air heat exchangerwhere it is partly cooled by heatexchange with cold outgoing air. Theair then passes to the air-to-refrigerantheat exchanger, or evaporator, where,

HIROSSDXB1, Compressor2. Condenser3. Motor-fan4. Evaporator5. Separator6. Condensate drain7. Expansion capillary8. Filter - dryer9. Hot gas valve10. Air-to-air heat exchanger11. Suction gas muffler12. Fan pressure switch13. Dewpoint gauge

Diagram of the larger Polair range shows theair-to-air heat exchanger circuit.


by direct heat exchange withevaporating refrigerant, the compressedair is cooled to about 3C.

The water vapour thus condensed isseparated from the air stream andejected via an automatic drain trap. Thecold dry air then passes to the air-to-airheat exchanger where it is reheated bywarm incoming air before leaving thedryer and entering the compressed airsystem.

Efficient heat exchanger design andeffective pre-cooling/reheating not onlyreduces the cooling requirements fromthe evaporator (i.e. the running costs)but also delivers compressed air into theair main at near ambient temperaturesthus preventing the formation ofcondensation on the outside ofdistribution pipework.

Of course, it is not enough for the dryerto ensure that it cools the air to adewpoint of 3C under steady full loadconditions. The airflow and inlet temp-erature will always vary to a greater orlesser extent and the dryer must becapable of handling such a fluctuatingload and still maintain a constantdewpoint. The Hiross dryers offered byThomas Wright/Thorite all have a fullyautomatic system of control whichensures that the dewpoint remainsconstant from the full rated capacity

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right down to no-flow conditions.

Finally, it is important that the separatorbuilt in to the dryer is efficient,otherwise condensed water will be re-entrained into the compressed air.

SELECTION OF AREFRIGERATION TYPEDRYERIn order to select the right dryer for aninstallation four main parameters mustbe considered;- compressed air flow rate- air temperature at the inlet to dryer- working pressure- the ambient air temperature in the

vicinity of the dryerThe compressed air flow rate maysimply be that of the compressor forwhich the dryer is to be installed butnot necessarily.

If the dryer is to be located downstreamof the air receiver for example, themaximum flow rate through it may belower or even higher than the ratedoutput of the compressor. It is importantto seek the advice of your ThomasWright/Thorite representative in thisrespect.

The inlet temperature to the dryershould be as low as possible. At typicalvalues of inlet temperature a differenceof just 1C can mean a difference of

4% in the thermal load on the dryer.

Make sure therefore that the aftercooleris efficient, adequately sized and wellmaintained.

The capacity of the dryer is also affectedby the temperature of the ambient airaround it. It should be sited where it hasaccess to cool ambient air and thelocation should be well ventilated. Thecondenser fins of the dryer should bebrushed and cleaned on a regular basisin the same way as for an airblastaftercooler.

LOWER DEWPOINTWhile a dewpoint of 3C is adequatefor the vast majority of industrialapplications there are some for which alower dewpoint may be necessary, e.g.:

- handling systems for hygroscopicand some foods and beverages.

- instrumentation located out of doors.- systems with very extensive external

air mains subject to sub-zerotemperature.

- assembly of some electroniccomponents.

- special manufacturing processesrequiring extra dry air.

Drying systems suitable for theseapplications, together with the benefitsof drying, are covered in the nextsection.


The previous section discussed howwater is removed from a compressed airsystem simply, effectively andeconomically by the installation of arefrigeration type air dryer. It didhowever mention a number of specialistapplications which require compressedair at very low dewpoints. Suchdewpoints cannot be achieved bycooling so a different type of dryer mustbe employed. There are two main types:deliquescent and desiccant.

DELIQUESCENT DRYERSDeliquescent dryers will reduce thepressure dewpoint to approx. -16C: theactual figure achieved will depend uponthe inlet air temperature and a numberof other factors. They operate bypassing air through a vessel filled withchemical pellets which graduallydissolve. The pellet stock requiresregular servicing: the rate varies withconditions but it is not unusual for totalreplacement within a matter of months.

A deliquescent dryer should be fittedwith an oil-removal filter immediatelyupstream because of the adverse effectof oil in any form on the pellets: a highquality after-filter, either integral orseparate, is also essential because of thecorrosive potential of the dissolvedsolution.

DESICCANT DRYERSThese units are able to providecompressed air at a pressure dewpointas low as -40C. This dewpoint cannotbe measured as a temperature: it is adegree of dryness that would have beenachieved if the air temperature hadactually been reduced to the statedlevel. Desiccant dryers employ granulesof a special material which extract watervapour from compressed air byattraction and adhesion of gaseous andliquid molecules to their surfaces. Thisprocess is termed adsorption. Thegranules can then be regenerated byextraction of the stored water. There aretwo basic types of desiccant dryers:heated and heatless so namedbecause of the different processes theyemploy for regeneration of thedesiccant.

ComprComprComprComprCompressed air conditioningessed air conditioningessed air conditioningessed air conditioningessed air conditioningDELIQUESCENT AND DESICCANT DRYERS

With both designs, wet air enters at theinlet of the unit and is diverted to theselected adsorber where it is dried priorto leaving by way of a check valve. Theadsorber is sized to dry a given air flowfor a fixed period during which time theother adsorber is reactivated andpressurised.

HEATLESS DRYERSHeatless dryers work on the principleof utilising the heat created byadsorption to assist in the regenerationof spent desiccant. Expanded dry air ispassed through the spent adsorber andcarries the desorbed moisture out of thesystem. Units of this type consist of twoadsorbers connected in parallel througha main diversion valve on the inlet andopposing check valves on the outlet.

HEAT REACTIVATEDDRYERSThese dryers operate on the internallyheated plus dry purge air principle. Heatsupplied to a wet adsorber (by electricresistance heaters or steam coils)liberates the moisture from the pores ofthe desiccant and the dry air carries itto waste. Like heatless dryers theseunits also consist of two adsorbersconnected in parallel through a main

diversion valve. Approximately 3 - 5%of the total compressed air throughputis required to supplement the heatapplied and regenerate the inactiveadsorber. With both types of desiccantdryer, the inactive adsorber ispressurised prior to being put back onstream.

Running costs for both are considerablygreater than for a refrigeration dryer ofthe same capacity. The granulesthemselves, furthermore, do not last forever: replacement every 10,000 hoursis advisable. It is important to bear thesepoints in mind when selecting a dryersystem.

ECONOMICINSTALLATION OF ADRYER SYSTEMAs has already been explained, for themajority of applications, a pressuredewpoint of 3C is more than adequateand, if lower dewpoints are required,they may not be necessary all yearround. It is also often the case that, evenif some processes or machines requirevery low dewpoint air, there are manymore areas of the factory where adewpoint of 3C is sufficient.


ComprComprComprComprCompressed air conditioningessed air conditioningessed air conditioningessed air conditioningessed air conditioningDELIQUESCENT AND DESICCANT DRYERSIt is for circumstances such as these thata combined drying system should beconsidered.

COMBINED SYSTEMIn such a system, all the compressed airproduced is dried at source using arefrigeration dryer. Areas and processesrequiring very low dewpoint air, forwhatever reason, can be satisfied by the

installation of smaller point-of-usedesiccant dryers. These desiccantdryers, with their relatively highrunning costs, need only be used whenambient temperatures are low, or whenprocesses requiring extra low dewpointair are in operation.

At other times the plant is protectedfrom all the problems associated with

wet compressed air by the refrigerationdryer installed at source. This dryer withits much lower running costs not onlyyields a more cost-effective dryingsystem but also takes the bulk of theload off the point-of-use desiccantdryers thus greatly reducing theirrunning costs, in turn.

WHY DRY COMPRESSED AIR?Water in compressed air causes rust, corrosion, wastage of air and many other problemseven before the air is used. All these problems cost money. How many of the followingproblems do you accept?

! Rust! Extra air cylinder maintenance! Corrosion of air main! Paint spraying blemishes! Deliberate wastage of air! Lubricator malfunction! Extra air motor maintenance! Corrosion of air receiver! Accidental wastage of air! Factory downtime! Pneumatic instrument inaccuracy! Emulsification of compressor oil! Extra air system maintenance! Product spoilage


ComprComprComprComprCompressed air conditioningessed air conditioningessed air conditioningessed air conditioningessed air conditioningFILTRATION

One final problem remains: oil and dirtin the line. The oil in question is notthe cool clean oil which is put into thesystem at the point-of-use to lubricateair tools, cylinders etc. but hot highpressure oil which is discharged into thedistribution system by the aircompressor. The latter is not suited tothe lubrication of air tools.

We must consider two fundamentalpoints:- compressor oil carry-over must not beallowed into the air system.- filtration is the only way to ensure itseffective removal.

It must also be remembered that dirt,fumes and other impurities are presentin the ambient air which is drawn intothe air compressor, Only a limitedquantity of the coarser particles can beremoved by the intake filter and the restare concentrated by the compressionprocess. Also, pipework prior to thedryer will deposit rust scale, gasketmaterial etc. into the air stream.

To ensure contaminant-free compressedair, filters must be used in conjunctionwith aftercoolers, separators and dryers.Each item has its own function toperform and when installed correctlyeach will complement the other.

FILTER ELEMENTSFilter elements are manufactured invarious forms to suit particularapplications, be it a very coarse pre-filter or an activated carbon element toremove odours and vapours.

Prefilters - The removal of bulk liquidsand particles. Generally these filtersperform a mechanical function i.e. theelements are manufactured from aporous material which sieves particlesfrom the air stream. These filters alsoprotect subsequent finer filters.

Fine Filters - The removal of micro-scopic droplets of liquid, aerosols anddust.

The operation of these filters is basedupon three different actions:

a) direct interception - larger particles

collide with the filter media and arethereby removed from the airstream.

b) inertial impact - successive changesin direction of smaller particles as theyencounter filter media fibres will leadto their progressive loss of energy untilthey finally adhere to a filter fibre.

c) Brownian diffusion - the randommovement of smaller particles causingthem to coalesce into larger ones dueto electrostatic or intermolecular forces.

The coalesced liquid particles arepushed by the airflow towards the out-side of the element. An anti-re-entrainment and shock resistant barrierprevents them from being reabsorbedinto the air stream and causes them todrain to the lower part of the elementfrom where they are discharged fromthe filter casing.

Activated Carbon Filters - Odours andvapours are removed by a process ofadsorption. The larger the surface areaexposed to the air flow, the moreefficient is this process. For this reasonthe element comprises a cartridge madeof layers of finely ground and highlypermeable activated carbon.

The Hiross Hyperfilter range includesthe grades of filtration referred to aboveand covers flow rates from 15 cfm toover 6000 cfm and is stocked by all ourbranches.

FILTER SELECTION ANDINSTALLATIONThe efficiency and cost effectiveness ofa filtration system depends upon thecorrect selection and installation of theindividual components. The followingsuggestions are the result of many yearsexperience in this field.- When selecting a grade of filter, notonly must the required air quality beknown but also the existing air quality.This will allow for adequateprefiltration to be installed.

- Choose the filter corresponding to themaximum flow and minimum operatingpressure expected at the point offiltration.

- When installing filters in existingpipelines choose a filter size whichcorresponds to the existing pipe sizeeven if the filter is oversized. This willlead to minimal pressure drop andextended life.

- Install filters at a point where the airis sufficiently cool - not only tomaximise the element life but also toallow contaminants in vapour form tocondense in order for the filter to actupon them.

- Provide enough space for thesubsequent removal of the filter casingto allow ease of element replacement.

- Always install filters with amechanism which indicates the airpressure drop across the element. Thiswill indicate its working efficiency andensure that the element is replaced ontime, i.e. not too late - and not too soon!

- Always be aware of the different usesto which air from a single aircompressor is put, e.g. a generalpurpose filter may be installed in afactory air main, but should some of thatair be used for breathing purposes, orcome into contact with food, thensecondary point-of-use filtration mustbe installed.

The uses to which compressed air is putare many and varied but, in most cases,the single most effective step acompressed air user can take to reducethe running costs of his system is toinstall the right equipment to removeoil and water.


So far we have dealt with the variousfactors affecting the selection of aircompressors, aftercoolers, dryers andfilters, it therefore seems logical to endwith some hints on how to transport thecompressed air from the compressorplant to the final points of use.

Frequently the installation of thecompressed air pipe system representsa large proportion of initial capital costsof a compressed air installation andtherefore careful consideration shouldbe given to ensuring that it is designedand installed correctly, in order tominimise high operational cost in thefuture. There are three main parametersto consider:

1. Lowest possible pressure lossbetween compressor plant and points ofair consumption

2. Minimum leakage

3. Efficient separation of condensatethroughout the system.

Loss of pressure through the pipesystem results in either decrease ofpower to tools and appliances andinefficient operation, or having to runcompressor plant at higher pressurethan normal in order to obtain correctworking pressures at tools andappliances thereby creating higherrunning cost of compressor plant.

To keep pressure loss to an acceptableminimum level the pipework should beof adequate internal dimensions and asdirect as possible. Where restrictions to,or changes in direction of, air flowoccur, such as through valves andfittings, the valves should be full flowtype and sweep type bends and teepieces should be used.

Allowance should be made for anyfuture increase in compressor outputand/or extensions to the pipe system.The cost of installing pipes and fittingsof larger diameters than are strictlynecessary at the outset is slightcompared with the cost of changing tolarger dimensions at a later date.

Leaks from a pipe system arecontinuous, whereas tools andappliances on average only operate 40- 50% of the time. A leak, therefore,consumes twice the power of a tool withthe same momentary consumption. Aleak equivalent to a 3mm hole (l/S dia.)in a pipe containing 7 bar (100 PSI)pressure will lose 3.36 kW (5 H.P) ofelectrical energy. Pipelines shouldtherefore be accessible so that they canbe maintained easily.

The main pipes should slope in thedirection of air flow by a gradient of1%. On long runs the pipe can revert toits original height by fitting a drain leg

and 2 long sweep bends. Drain legsfitted with either manual or automaticdrain valves should be fitted at all lowparts of the pipe system.

Pipework should be adequatelysupported throughout its entire lengthand where materials with a high rate ofthermal expansion are used allowancemust be made for movement in orderto relieve possible stresses occurring inthe pipework. Main air lines may besited at any level but it is generallyfound best to place them at high levelas this practice affords easy access andgood draining facilities. The speed ofair flow through main line pipeworkshould be less than 6 m/sec. and speedin final feed lines to tools andappliances that do not exceed 15 metresin length should be less than 15 m/sec.

These air flow rates can be assessedusing the following formula:

Main Line piping.

V = 1273Q(P+1)D2

where

V = Flow velocity in Metres/SecondQ = Free air flow in Litres/SecondP = Air Pressure in Bar (Gauge)D = Pipe Internal Diameter in mm.

Alternatively, if the free air flow isknown the minimum diameter of the air

ComprComprComprComprCompressed air systemsessed air systemsessed air systemsessed air systemsessed air systemsINSTALLATION

AIR FLOW THROUGH NOZZLES

NOTES:1. The data right is based on 100%

flow coefficient for a well roundednozzle entrance; multiply thesevalues by 0.96 where nozzles havesharp edged entry.

2. Values should be multiplied by0.65 for approximate results withnon-circular shapes.

3. Volume of air in L/s at 1 bar and15C

4. Pressure (bar) is gauge pressure.


ComprComprComprComprCompressed air systemsessed air systemsessed air systemsessed air systemsessed air systemsINSTALLATION

main to ensure velocities below 6m/seccan be found from the following

D = 212 Q(P+1)

Maximum permissible flow in branchfeed lines may be found by using

Q = (P+1) D285

There are two basic systems forcompressed air mains:1. A single line from supply to point(s)of usage2. A closed loop circuit (ring main)

For installations where the point ofsupply and usage are relatively close, asingle direct line will suffice. In thiscase the diameter of the pipe must becapable of carrying the maximum flowwith no more than the maximumacceptable pressure drop. Forinstallations with numerous take offpoints which are not relatively adjacentto each other a closed loop (ring main)system has advantages in that thevelocity of air flow to any one point isreduced, since the air can converge onthat point from two directions; also, bycorrect siting of isolating valves in themain line, it can be made possible toclose down a section at a time formaintenance or emergency repair workwhilst leaving the remainder of thesystem operational.

Feed lines to tools and machineryshould be taken from the top of the mainand sweep bends used to drop the lineto a working height. An isolation valveshould be fitted which is easilyaccessible. It is important that the finalpressure to tool or appliance does notfall below minimum requirements. Thefeed line and items such as isolationvalves, quick acting couplers andflexible hoses should therefore be ofsufficient diameter to carry the requiredflow rate.

Piping materials can be of steel, copper,A.B.S. or thin-wall stainless steel.Copper and stainless steel are usuallyused for systems below 25 mm diameteror final drop feed lines,

Steel pipe, when used, should be toBS1387. This is available in black orgalvanized form. The latter isrecommended as it is less liable tocorrode. It can be screwed to acceptproprietary malleable fittings whichshould conform with BS 143 or BS1256. For piping over 65mm bore,welded type fittings are recommended.

A.B.S. pipe suitable for use withcompressed air is available. It isextremely tough and ductile and is selfcoloured light blue (the recommendedcolour for compressed air lines). It hasgood flow characteristics. As with allthermoplastics, A.B.S. has a limited

temperature range. A.B.S. pipe must notbe threaded.

A full range of fittings are available,joints being made by solvent fusion.Only jointing compound compatiblewith A.B.S. should be used. Mostsynthetic oils and a few mineral oils willdegrade thermoplastics and elastomersand therefore oil suitability must bechecked with pipework suppliers.

Experience has proved that plannedmaintenance of compressed air plantpays great dividends and likewise thesame is equally true regarding the airdistribution system.

Pressure gauges or test points at criticalparts of the system and at final usagepoints will give easy indication ofpressure losses and leak rates can bemonitored at regular intervals bymeasuring the quantity of air deliveredby the compressor to maintain normalpressure when all outlet points areturned off. In addition to this, regularinspection of couplings, hoses andpneumatically operated appliancesshould be made to locate and, if needbe, correct leakage.

Compressed air is a valuable source ofpower, its efficient use will increaseyour profits. If you wish to check theefficiency of your existing systemplease contact our TechnicalDepartments in Bradford or Leeds.

RECOMMENDED AIR FLOWS THROUGH MEDIUM WEIGHT BS1387 STEEL PIPE


EXAMPLEIn order to give a practical example of how to use the infor-mation contained in this guide let us consider a hypothetical,new, medium sized production factory and work through thefactors that we need to consider in order to ascertain thecompressed air plant requirements. The factory will be oncontinuous production cycle.

ASSESSING VOLUME REQUIREDPRODUCTION DEPT.Two machines.Refer to Cylinder Consumption Table 11 machine using 2 off 160mm bore cylinders with 75mmstroke operating at 2 times/minute.160mm bore = 0.13 litres per mm strokeTherefore 0.13 x 75mm stroke x 2 strokes/cycle =19.75 x 2ops/minute x 2 off cylinders = 78L/M (1.3L/s).1 machine using 4 off 100mm bore x 50mm stroke cylindersat 15 ops/minute0.051 x 50 x 2 x 15 x 4 = 306 L/M (5.1 L/s).Total Consumption Production Dept. = 6.4 L/s

ASSEMBLY SHOPRefer to Tool Consumption Table 2

Qty Item Column 1 Col. 2 Col. 3 Total2 Drills Medium 8 L/s 0.20 1.6 L/s 3.2 L/s2 Drills Light 6 L/s 0.20 1.2 L/s 2.4 L/s2 Imp. wrenches 23 L/s 0.10 2.3 L/s 4.6 L/s

Total Consumption Assembly Shop = 10.2 L/s

PREPARATION DEPT.2 Orbital sanders 11.0 L/s 0.50 5.5 L/s 11.0 L/s

FINISHING DEPT.2 Spray Guns 7 .0 L/s 0.50 3.5 L/s 7.0 L/s

GENERAL3 Blow Guns 8.0 L/s 0.10 0.8 L/s 2.4 L/s

Average Consumption Required = 37.0 L/sAdd 25% for future expansion = 46.25 L/sAdd 5% Allowance for Leakage = 48.56 L/sTotal Factory Requirement = 48.56 L/sTo convert L/s - CFM. multiply by 0.03531 and then by 60.

OPERATING PRESSURERefer to Page 5

Production Dept. requires 5.5 Bar Gauge.Assembly & Preparation Depts. need 6 Bar Gauge.Finishing Dept. 3.5 Bar Gauge, Blow Guns 2 Bar Gauge.Therefore Maximum Pressure required is 6 bar gauge.Allow for transmission losses and compressor controldifferential - use compressor with minimum working pressureof 7 bar gauge. Note 1 Bar = 14.7 pounds/Square Inch (P.S.I.)

FREQUENCY OF AIR DEMANDIs air demand continuous or variable? In this case it iscontinuous production therefore we would recommend a vaneor screw type compressor in preference to a reciprocatingtype. Refer to Pages 4 & 5.

ENVIRONMENTAL CONDITIONSRefer to Page 5.

They need to be clean, cool, well ventilated, with adequateroom for maintenance and repairs. Consider local noise levelrestrictions. In this instance the vane or screw compressorsrecommended have much lower noise levels than thereciprocating types.

QUALITY OF COMPRESSOR AIRREQUIREDConsider the financial benefits of getting rid of condensateand oil carry over by fitting a dryer aud main line filtration.Refer to Pages 5 and 6 and Pages 9 to 14.

Consider the dewpoint required in order to choose the correcttype of dryer. Do not use a lower dewpoint than is reallynecessary as it will increase the running costs without givingany added advantages. In our example the compressor plantis in the same building (no outside air lines) and there is noapplication requiring a very low dewpoint, so a refrigerationdryer would satisfy the requirements.

FILTRATIONWe would need a general purpose filter but there is noapplication requiring the removal of oil vapour or odour soan oil filter down to 0.01 PPM will suffice.

INSTALLATIQN OF COMPRESSORPLANTConsider unloading facilities and electrical requirements ofcompressor and dryer.COMPRESSOR STAND-BY CAPACITYConsider the importance of air supply in relation to needs.Will serious loss be involved if air supply fails? In aproduction plant the answer is Yes. Therefore we need morethan one compressor so that production is not lost duringperiods of maintenance or breakdown.

IS THE FACTORY DEMAND VARIABLE?If so we would need a multiple of smaller compressors whichwould switch on and off automatically according to airdemand and thereby save energy.

In our example it is continuous production so we only need2 compressors - 1 on duty and 1 on stand-by.

ComprComprComprComprCompressed air systemsessed air systemsessed air systemsessed air systemsessed air systemsASSESSMENT OF COMPRESSOR PLANT


SERVICINGAre spares and service easily available? Also considerpreventive maintenance i.e. A contract service facility.

MAIN FACTORY PIPING SYSTEMRefer to Pages 17 and 18.

In our example an ideal, reliable system would need:2 off 25 H.P. vane or screw compressors. 50 L/s (106 CFM)1 off Vertical air receiver to match would be 500 litres (17cu.ft.) capacity1 off Refrigeration dryer. Minimum flow at 30C inlet temp.1 off General purpose filter1 off Oil removal filter to 0.01 PPMFactory Piping would be closed loop (Ring Main)2" N.B. Pipe for mains with l/2" drop feed linesDryer and Filters would have a 3-valved bypass system.Filters would have pressure drop indicators to indicate needto change elements.Automatic Drain Valves on receiver, aftercooler and filters.

ComprComprComprComprCompressed air systemsessed air systemsessed air systemsessed air systemsessed air systemsEXAMPLE

PREFERRED METRIC UNITSCompressor and tool manufacturers prefer Litres, up to 1000(L) and cubic metres (M3) above 1000L

Pneumatic equipment manufacturers prefer cubic decimetres,dm3.

Normally quoted as Free Air at specified conditions in thecase of air compressors, the conditions are those prevailingat the air compressor inlet.

For pneumatic tools and control equipment the conditionsare those at standard reference atmosphere (ANR). Use ofthe letters ANR (Atmosphere Normale De Reference) afterthe rate of flow indicates that the flow is Free Air at standardatmosphere conditions. Unless otherwise stated pressures inBar are assumed to be gauge pressures.

References for further information on S.I. units are ISOlOOO,

BS5555, CETOP RP71 and BSI Publication PD 5686 1978.

A TYPICAL COMPRESSED AIR PIPEWORK SYSTEM

CORRECT AIRLINE INSTALLATION


ComprComprComprComprCompressed air systemsessed air systemsessed air systemsessed air systemsessed air systemsPRESSURE SYSTEMS REGULATIONSPressure Systems and Transportable Gas Container Regulations 1989Statutory Instrument 1989 No. 2169The above Regulations came into force on 1st. July 1990 and as a user/owner of a compressed air system you are directlyresponsible for ensuring that your system complies with these regulations. One of your responsibilities will be to draw up,or certify a written scheme of examination for your air system, which must be carried out by a legally competent person.

Whom does it affect?Owners and Users of compressed air installed or portable, existing or new

Those who design compressed air systems and components:

Those who manufacture compressed air systems and components

Those who install compressed air systems

Those who maintain compressed air systems

Those who import compressed air systems and components

Those who supply compressed air systems

Competent Persons and Examiners

Components which should be included in each Scheme of Examination1. Air receivers.

2. Air/Oil separator vessels of screw compressors.

3. Pressure relief valves (Safety Valves).

4. Pressure gauges and temperature gauges.

5. Filters and lubricators with plastic bowls.

6. Filters and automatic drain valves with metal bowls.

7. Pressure switches if failure could give rise to danger.

8. Oil and/or air temperature controls of compressors.

9. Oil level controls of oil flooded compressors.

10. Intercoolers of two stage compressors.

11. Pipework of reciprocating compressors between compressor and aftercooler

12. Any metallic pipework which is located in a position where,failure couldgive rise to personal injury

13. Fusible plugs and bursting discs.

14. Any aftercoolers with headers exceeding 250 bar litres.

15. Pressure regulators if regulator failure could result in the rupture of thedownstream pipework or equipment

Our Company is a Competent Person as defined in the Pressure SystemsLegislation and is therefore fully qualified to draw up a Written Scheme ofExamination and to carry out such examinations.If you require advice, or are in doubt regarding your responsibilities under theseregulations or if you wish us to act as your Competent Person please do nothesitate to contact any of our Centres listed on the back page.

Suggested ReadingThe British Compressed Air Society have published a guidance and interpretation document covering these Regulationswhich is available from our Group of Companies entitled Owners and Users Guide Part 4.


AIR CYLINDER AND AIR TOOL CONSUMPTIONSCOMPRESSED AIR SYSTEMS

AIR CYLINDER AND AIR TOOL CONSUMPTIONS

TABLE1AIR CYLINDER THRUSTS AND

CONSUMPTIONS

0 0 approx Thrustmm inches Newtons

250 10 27080

200 8 17330

160 6 1/4 11090

125 5 6770

100 4 4330

80 3 1/8 2770

63 2 1/2 1720

50 2 1080

40 1 1/2 693

32 1 1/4/, 443

25 1 270

20 3/4 173

16 5/8 111

12 1/2 62.4

Thrust

lb.

6085

3895

2490

1520

973

623

386

243

156

100

61

39

25

14

Air Usage- litres

per mm stroke

.316

.202

.130

.079

.051

.032

.020

.013

.OO81

.OO52

.OO32

.0020

OO13

.0007For cylinders smaller than 012. theoretically derived figures become

meaningless because of the increased significance of factors which may

safely be ignored in cylinders of larger diameter. Figures apply to non-

cushioned cylinders at 80 psi (5.52 bar)

Thrust - varies directly with pressure. At 60 psi, thrusts arethree-quarters of those shown: for thrusts exerted by cylindersfed with air at 100 psi, multiply figures from the table by 1.25.

Thrusts given are gross theoretical; as a rule of thumb, whenselecting cylinders multiply required thrust by 1.5 thenchoose the next larger bore.

Example: Thrust required - 400 lb. Pressure available - 80 psi.

400 x I .5 = 600. Therefore use 080 cylinder (delivers 623 lb.)

4ir Consumption - is given in litres of free air per mm ofstroke. To convert litres to cubic feet, multiply by 0.0353.

Example: What is the air consumption for a cylinder 080,IOOmm stroke, supplied with air at 80 psi, for three completecycles (extend + retract)?

3.032 x 100 x 3 x 2 = 19.2 L/s 19.2 x 0.0353 = 0.678 cu. ft

Consumption will be greater at pressures higher than 80 psi,less at lower pressures.

TABLE2AIR CONSUMPTIONS OF AIR TOOLS

The table gives typical free air consumption figures for airtools and appliances. *These figures are governed by the sizeof nozzle used.

When assessing compressor requirements it is important tawork with the compressor manufacturers F.A.D.characteristic which states the actual Free Air Delivered. Itshould also be remembered that consumption tends tcincrease as tools age.

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Compressed Air Installation Guide