Chapter II the Centrifugal Fire Pump

8/3/2019 Chapter II the Centrifugal Fire Pump

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CENTRIFUGAL FIRE PUMP

CHAPTER IITHE CENTRIFUGAL FIRE PUMPA pump can be describedas "any ofvarious mechanical devices which utilize an external sourceof power to apply a force to a liquid or gas". There are many types of these devices, eachsuitedto a particular purpose, with none universally best for all applications. Pumps can generally becategorized into two basic groupings, according to whether they discharge liquid or gas involumes separatedby a period of no discharge positive displacement), or in a continuous flow(non-positive displacement).A positive displacement pump dischargesa definite volume of liquid or gas in each cycle ofpump operation, provided that the motive force driving the pump is greater han any resistanceoffered to the movement of the material being actedupon. The rotary vane priming pump is sucha pump. The vanes create chambers n the casing of the pump. This separation of the liquid orgas is constant due to the definite volume of each chamber and must have a open dischargeoutlet. If the discharge outlet of a positive displacement type pump, when pumping anincompressible material, were completely closed, either the driving force would be stalled, orsomething would break.A non-positive displacementpump in operation dischargesa volume of liquid in each cycle ofoperation which is dependentupon the resistanceoffered to the movement of the liquid beingpumped. This type of pump exerts a force upon the liquid that is constant for any given speedof the pump. When a resistanceequal to the force being exerted by the pump is presented o itsdischarge, the material reaches a state of equilibrium and does not move. This is due to thedesign of the pump casing area which allows the impeller to move freely without dischargingwater. Nothing more will happen,except hat the pump will chum the liquid, there by generatingheat.One ype of non-positive displacementpump applies an action to liquids by rotating them n sucha manner as o achieve a centrifugal force (the force tending to make rotating bodies move awayfrom the center ofrotation). This type ofpump is referred to as a "centrifugal pump". The basicprinciples ofhow a centrifugal pump developsvelocity and pressure,aswell as he basic designsof a centrifugal pump, are explained in this chapterIf a small amount of water is placed at the center of a rapidly rotating turntable, it would bethrown off. In other words, the turntable will impart horizontal radial velocity to the water. Thefaster the turntable is rotated, the further the water will be thrown, due to more velocity beingimparted to the water

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Should some water be placed n a container and then rotated on the turntable, as n Figure l, thewater at the center of the container would begin to move outward. However, the water at theouter edge cannot move outward becauseof the walls of the container, so it moves upward;which shows that pressure has been created in the water. The height to which it goes, (thepressure hat is created) dependsupon the speedof rotation. Therefore, by confining the water,the velocity imparted by the turntable is converted o pressure. n this illustration there was nowater either entering or leaving the container, so all of the velocity must have been convertedinto pressure.

TURNT ABLE AND GLASS PICTUREIGURE 1:The centrifugal pump employs an impeller as the means of imparting velocity to the water thatenters the pump. This impeller is mounted on a shaft, which is turned by a motive force. Figure2, shows one view of a typical impeller. In operation, water is introduced at the center inlet ofthe rapidly rotating impeller; is partially confined by the sides and vanes of the impeller; and isthrown by centrifugal force to the outer edge. Its path of travel is not a straight line however; dueto the rotation of the impeller, it takes a spiral path through the impeller. Since the outer edgeof the impeller is traveling at a much faster rate than the edge of the inlet, additional velocity isimparted to the water as it approaches the outer rim. This tangential velocity increase occursbecause the radius of the water path spiral increases and the water travels a greater distance perrevolution

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Front Shroud.ack Shroud

S-lin. Rin.

IMPELLER.IGURE 2:

There are vanes ocated between the two sides of the impeller which play an important part inthe design of the impeller. Thesevanesprevent eddying of the water, ( a current at variance withthe main current); and by presenting a constantly enlarging area between themselves as theyapproach he outer rim, allowing partial conversion of velocity to pressure. t will be noted thatthese vanes are curved away from the direction of rotation (Figure 2, impeller designed forcounterclockwise rotation) in order not to interfere with the natural movement of the water fromthe center to the outer edge as the impeller rotates. In this way the maximum efficiency of theimpeller is obtained.By locating the impeller in a chamber of a particular design, the basic configuration of a pumpis created. This chamber collects the water being thrown tangentially ( change of direction) fromthe outer edge of the impeller as it rotates.The impeller is positioned eccentric ( off center) o the pump casing, so that the areabetween heouter edge of the impeller and the wall of the pump casing is constantly increasing as itapproaches he discharge outlet. This produces what is known as a "volute", Figure 3.

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This constantly enlarging area isnecessary because water is thrownfrom the impeller around its entirecircumference and the total quantity ofwater passing through the chamber isincreasingly greater toward thedischarge outlet, Figure 3. The volutedesign of a centrifugal fire pumppermits the water passing through thegradually enlarging area to be reducedin velocity with a corresponding..Increase In pressure.

The water in the discharge area of thevolute casing is prevented fromreturning to the intake area of theimpeller by the close fit between a Pi~r. 3 ! Vn' , , r --clearance ring fitted in the pump c'asing, Figure 3: Voluteand either the hub of the impeller, or another-clearance ring attached to the impeller, Figure 2(Sealing Rings).Since this clearance s very small and the impeller is turning at a high rate of speed, t is veryimportant that the pump should not be run without water in it, or run for a long period of timewithout discharging water. This would cause he pump to overheat and expansion would takeup the clearancebetween the rings. The rings would then make contact and seize, resulting indamage o the pump and possibly to the drive mechanismbetween motive force and thepump.The impeller of a centrifugal pump must be rotated at a high rate of speed to develop thedesired volume and pressure. Most pump impellers rotate approximately at a (2: 1) ratio to theengine speed. For this reason, the speed of the motor should be increased and decreasedgradually to prevent damage to the pump shaft and gears of the pump transmission, and toavoid sudden changes in pressure developed by the pump.There are no blockages within the pump proper, and a continuous waterway is presentedthrough the pump from the suction inlet to the discharge outlet. Passageways through theimpeller are small, however, and are subject to clogging if foreign matter is permitted to enterthe pump. Since clogging of the impeller will seriously affect the operation of the pump,extreme care should be taken that the proper strainers are in place to catch such foreignmatter. Specifically when receiving a water supply from a non-municipal water source(rivers, ponds, etc.) 11-4


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In understanding he principles and behavioral patterns of centrifugal pumps, it is necessaryto remember the following points:Since the sizes and areasof impellers are fixed in the design and construction, andtherefore not variable within a given pump; the ratio between the velocity of waterentering the impeller and the velocity of water leaving the impeller at any given flowis always constant.

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2. The velocity of water entering the impeller dependsupon the revolutions per minute(rpm) of the impeller. It follow that since a rotating impeller with unrestricteddischarge mparts velocity to water, the velocity of water leaving the mpeller dependsupon the revolutions per minute (rpm) of the impeller.

3 The quantity of water discharged rom a pump is directly related to the ratio betweenentrance and exit velocities as well as the velocity of water entering the pump. Sincethe ratio is fixed and constant at a given flow, and the entrance velocity dependsuponthe rpm of the impeller; it would follow that, within the physical capabilities of thepump itself, with the dischargepressurebeing held constant; the greater the rpm of theimpeller, the greater the velocity , and, the greater he velocity, the greater hedischarge quantity .4. The increase n pressuredependsupon the same wo factors; (a) The ratio of enteringvelocity to exit velocity, and, (b) the velocity ofwater entering the impeller. Item (a)is constant for any given pump, and item (b) is variable, depending upon the rpm ofthe impeller. Therefore, within the physical capabilities of the pump itself, with thequantity discharge being held constant; he greater he rpm of the impeller, the greaterthe gain in discharge-pressure.5. It should be noted that 3 and 4 together ndicate that both quantity and pressurevarydirectly with the rpm of the impeller. However, quantity and pressure are interrelatedand their development n the pump occurs simultaneously. Therefore, within thephysical capabilities of the pump itself; when the rpm of the impeller is increased,both quantity and pressureoutputs increase,and, when the rpm of the impeller isdecreased,both quantity and pressureoutputs decrease.6 The discharge pressure or a centrifugal pump is equal to the change n pressurewhichthe pump itself can create,plus the pressureat the intake.

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Item 6 indicates that we can place centrifugal pumps in series and each successivepumpwould add its increment of pressure o the entire discharge pressureof the previous one. Thiscan be taken advantageof in lon:g elays ofwater from the source to the fire ground.It is necessary or the fire servic(~ o have some means of imparting velocity to water toobtain a desired quantity of discharge as well as some means of creating pressure n order toprovide nozzle pressure and overcome friction loss in the hose ines leading from thepumping apparatus..Centrifugal pumps can supply different volumes of water while runningat a constant speed,since the volume of dischargevaries with the resistanceagainst whichthe water must be discharged. A properly designedcentrifugal pump can create he pressuresnecessary or fire fighting activitjes. Centrifugal pumps can take advantageof intakepressures,a fact that proves very beneficial to fireground operations. They can run withoutpressure elief devices without doing structural damage o the pump. The initial cost of acentrifugal pump is considerable ess than other comparablepumps. All in all, centrifugalpumps possess he attributes desired and required for fire fighting applications.All of the pumping apparatus n 'theDistrict of Columbia Fire and EMS Department areequipped with centrifugal pumps:.They are all constructed o incorporate some of themechanical features previously reviewed, i.e., all impellers are in volute casings; all haveclearance ings, and all have a separatepriming system o enable them to draft water.The centrifugal fire pumps in this department,are single-stagecentrifugal pumps.

SINGLE STAGE PUMPSThe single-stagepumps in this d~~partmentre rated at either 1250 or 1500 gallons perminute, at 150 pounds per squar~:nch. The single-stagecentrifugal pump has evolved overtime to be an efficient centrifugal pump for the work to be accomplished. Preceding hesingle-stagepump was the two-stage pump which is still in use and will be touched on laterfor the purpose of understanding he principles of the centrifugal pump.In operation, the single-stage, centrifugal pump has a minimum ofcontrols. The enginethrottle control and discharge ga1:e alves control the volume discharged at any desiredpressurewithin the design capacilty ange. Water enters he eye of the impeller from thesuction chamber, flowing in an axial direction, (Parallel with the impeller shaft), making a 90degreechange n flow direction as t enters he impeller, which directs the flow in a radially

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outward direction to be picked up by the vanes n the impeller, FIGURE 4. An end thrust isproduced as the flow direction i~.abruptly changed, or which some compensationmust bemade to keep the thrust load within the load limits of the bearings.

DISCHARGE

FIGURE 4: WATERFLOW'THROUGHIMPELLER

To approximately balance this h:ydraulic hrust, clearance ings are provided in the housing atthe back side of the impeller. The rings are about same diameter as the clearance ings in thehousing at the eye of the impeller. Holes are provided in the rear wall of the impeller,between he hub and the edge of the vanes o admit water to the back side of the impeller.The provision for partial hydraulic balance reducesend-thrust so that any difference can beabsorbedby the impeller SUppOr1tearings. -In a singJe-stage, entrifugal pump, the impeller may be single-suction or a double-suctiontype. In designing a pump for fire service use, there is a practical limitation on physicaldimensions to permit vehicle mounting within the space equirements. Considerableattention is given to design characteristicswith reference o mounting location to efficientlysatisfy capacity rating requirements and provide the high lift characteristics essential n a firepump, the capacity rating for a single-stage,centrifugal pump with a single-suction impelleris usually limited to 750 G.P M.The double-suction impeller (figure 5), is in hydraulic balance due to the symmetry of designof each suction inlet. water enters each side of the impeller simultaneously, automaticallybalancing the end thrust. Double-suction impellers are used n fire pumps with high capacityratings. These mpellers develop a high efficiency. The double-suction impeller has also beenused n the parallel-series, two-s1tage entrifugal pump.

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Flow OperationWater enters suction channels A and Bwith equal separation of gallons Intoeach channel

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4~1~~jp-1 t.

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Figure S

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The double-suction impeller gives a volume reserve. This is what will be found on modemapparatus.Water is delivered to both sides of the impeller at the same ime, thus balancingthe impeller for axial thrust. Of mixed flow design, the impeller gives broad band efficiencyover full range of pumping performance, accurately machined, hand ground, and balanced.The single impeller design keeps waste friction horsepower to a minimum.Impeller shaft deflection, from unbalancedpressure n the volute housing, produces vibrationin the pump when operating, and may causeadded wear at the clearance ing and impellereye. Such deflection is also the causeof much packing wear, with a tendency to "bell mouth"the packing. To reduce these conditions, the double-volute, single-stage centrifugal fire pumpis introduced for fire service use, (figure 6).The dual volute for radial hydraulic balancewas engineered or rotational balance over thecomplete pumping range.The Double-volute design has been used formany years by pump manufacturersbuildingpumps for municipal and industrial watersupply systems,and has been proven highlysuccessful n reducing vibration, packingwear, and clearance ing wear, withconsequently ess maintenanceof the pump.The use of the double-volute design s ~Jonfined to the single-stagepump sinceno satisfactory design has been developed ouse the double-volute design in the parallel series,multi-stage, centrifugal pump.

~Figure 6: Double Volute/Double Suction

One of the features of the single-stagepump is its high efficiency at or near rated capacityThe best efficiency is usually above 70 percent, a few percent higher than any of the multistage,centrifugal pumps. The efficiency at a given discharge rate (GPM) is subject tovariation according to the dischargepressure PSI), and though the effects of the pressure ssmall when operating-at or near rated capacity at lower discharge rates with higher pressuresthe efficiency drops quite rapidly. The maximum or cut-off pressure or most single-stage,centrifugal fire pumps is in the range of375 to 450 P.S.l. At cut-off, the discharge s zerogallons per minute. The Departmentsmaximum dischargepressure s 300 psi.

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The double-volute, single-stage centrifugal pump, has a very high efficiency at ratedcapacity , but more important, the high efficiency prevails over a considerable range ofdischarge.Pump efficiency is important as t deten11ineshe amount of power required to be delivered tothe pump for a given output (gallons per minutes at specified pressure).While over 90percent of fire departmentpump operation is at reduced volume and pressure, he lowerpump efficiency at these rated reduced flows is not too important at non11al ressures; here isadequateengine power to produce the required volume and pressure.

TWQ-ST AGE PUMPSThe following is a brief explanation of the operation of the two-stage pump. These pumps arestill in use by the fire service but the single-stagepump is just as efficient with the design ofthe double intake, double volute system and the increaseduse of the diesel engine as a powersource which produces a greater torque. The single-stagepump is more common todaybecauseof its simplified operation.In operation of the two-stage series-parallel pump, the two impellers, such as described,aremounted on a single shaft so that they rotate at the same speedat the same ime. Eachimpeller is contained in its own volute casing which is interconnected with the other in such amanner that these wo impellers may be operatedeither in parallel or series. This change ofoperation is accomplished by means of a transfer valve and either one or two flap valves. Thetransfer valve is a device which closes or opens certain waterways within the confines of thepump housing.The transfer valve is placed in the volume or capacity position for the parallel operation ofthe two impellers. In this position each mpeller independently receives water from thesuction intake manifold and discharges t into the discharge outlet manifold. This is theoperation used when large quantities of water are desired at lower pressures.The transfer valve is placed in the pressureposition for the series operation of the twoimpellers. In this position, the first impeller receives water from the suction intake manifold,and its discharge s made to flow into the intake of the other impeller. The second mpellerthen discharges he water into the discharge outlet manifold.If pumping is already in progress and it becomes-necessaryo change from pressure ocapacity or vice-versa, the pump pressureshould be reduced to within 50 p .S.I. of the pumpintake pressure.

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With the transfer valve in the volume position, figure 7, water entering the suction intakedivides: half flowing to the first impeller, the other half opening the flap valve and flowing tothe inlet of the second impeller. The discharge from both impellers then goes directly to thedischarge outlet, each impeller pumping half the water at identical pressure.

\ "Figure 7: Volume Position

(With the transfer valve in the pressure position, figure 8,water enters suction intake andflows into the first impeller. From the discharge of first impeller, the water is directed by thetransfer valve into the inlet of the second impeller. At the same time, pressure from theimpeller, since it is greater than the pressure atthe suction intake, holds the flap valve closed.After adding an equal amount of pressure the second impeller discharges the water directly tothe discharge outlet.

Figure 8: PRESSURE POSITIONPRIMING PUMPS

i,The impeller on a centrifugal pump will not pump air alone, so the centrifugal pump cannotprime itself. Therefore, it is necessary to have somemeans of priming a centrifugal pump sothat it may draft water. This may be a small positive displacement type pump, an ejectorprimer, or some other type system.

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This Department currently uses a rotary vane positive displacement ype priming pumpwhich is found on HALE PUMPS. The rotary gear priming pump may still be found in useon fire apparatuspumps.

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This hole should be kept open, as t breaks the syphoning effect when the pump isdisengaged.The four to six quart capacity oil tank shall be kept full with S.A.E. 30 motor oil.Check oil level after each use.

Figure 11: Primer Oil ReservoirPriming pumps are either clutch or electrically driven. It is possible to operate some primingsystemswithout the main pump being engagedsince the motive power for the priming pumpis electrical. However, more dependableand rapid priming will occur with both pumpsengaged,and the operational steps or individual apparatur; eflect this process. Electricalpriming pumps are likely to be found on modern centrifugal pumps.Piping connects he priming pump intake to the eye of the impeller of the centrifugal pump.A cut-off, or priming valve, is provided in this pipe line which, when open, allows a clearpassagewayso that the priming pump can exhaust he air from the main pump. This valve,when closed, prevents any pressure n the main pump from being exerted against the primingpump. The priming valve is operatedby the same controlling handle that operates hepriming motor .The discharge rom the priming pump is made directly to the ground, thereby permitting theoperator to see when the main pump is primed. Because he priming pump is operating withthe main pump engaged,pressurewill be indicated on the discharge gauge when the mainpump is primed.

RELIEF V AL YEIf the centrifugal pump is supplying one line of hose with the playpipe open, and theplaypipe is then shut off, an increase n pump pressurewill occur which will result in anexcessive nitial nozzle reaction when the playpipe is again opened.Also, if a centrifugalpump is supplying two hose ines with the playpipes open, and the playpipe on one of thelines is then shut off, an

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increase n pump discharge pressurewill occur which will result in excessivenozzle pressureon the remaining line. The operation of the centrifugal pump is such that when the playpipeis closed, the engine load is decreasedbecause he pump is no longer discharging thatquantity of water resulting from a particular throttle setting and discharge opening. With theengine load thus reduced, the engine speed ncreases.When the engine speed ncreases, hepump speed ncreasesand pump pressure ises proportionately to the throttle setting.Such ncreasesare objectionable-becauseof potential serious njury to the f ire ightersholding the playpipe, and becauseof the possibility of the higher pressure upturing the hose.Therefore all centrifugal fire pumps are equipped with either an automatic governor or arelief valve. Either one, when properly set, will prevent the increase n pump pressure hatoccurs when a playpipe is closed, the automatic governor controls the fuel supply to theengine ( commonly used on gas engines), and by such control decreases he speedof theengine when the playpipe is closed, and increases he speedof the engine when the playpipeis again opened. This maintains the pressure or which the governor is set. This DeDartmentutilizes relief valves only. The relief valve maintains a constant oad on the engine byopening a passagewaybetween the discharge and suction sides of the pump when theplaypipe is closed, thus permitting water to churn from the discharge side to the suction sideof the pump. When the playpipe is again opened, hat passagewaycloses, and water isprevented from churning. With this relatively constant oad on the engine, its speed emainsrelatively constant, hus maintaining the pressure or which the relief valve is set.All pumping apparatus n this Department are equipped with a relief valve. There may beminor differences in the relief valves found throughout the Depa~ent, but all operatebasically the same. SeeFigure 12, for a schematic of one type relief valve.The complete relief valve assembly consists of a chum valve, which is contained within theconfiguration of the main pump housing; a control valve, which is mounted in a convenientoperating position on the side control panel of the apparatus;and a pilot light, the switchbeing located on the chum valve assembly, and the lamp being located on the side controlpanel of the apparatus.The chum valve resemblesa large double endedpiston with unequal face areas, .e., the flatarea on one end is larger than the flat area on the other end. This valve operates n such amanner that when pressure s applied at the larger end of the piston, it moves, and the otherend opens a passagewaybetween the discharge side and the suction side of the pump.

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The control valve may be slightly different fromone relief valve to the next, but all are basicallyoperatedby a handwheel which in turn eitherincreasesor decreases ension on the controlspnngs. -,--These wo valves are designed so that when thepressureon the discharge side of the pumpexceeds he pressureat which the controllingspring is set, the control valve opens. Thisallows the pump discharge pressure o open thechurn valve, permitting water to flow from thedischarge side of the pump to the suction side ofthe pump; thus relieving the dischargepressure.When the discharge pressuredrops below thesetting of the spring, the control valve closes,allowing the churn valve to close, and the flowfrom the discharge side of the suction side of thepump ceases.The relief valve is equipped with a pilot light,Figure 12: StandardReliefValve actuatedbythe pilot light switch on the chum valve. Withthe chum valve in the closed position, the pilotlight switch button is depressedby part of thechum valve assembly. When the chum valveopens, he button is released,allowing an electrical Figure 12: Standard ReliefValvecontact to be made which actuates he pilot lightlamp. While the lighted lamp is an effective gauge hat the chum valve has opened, t doesnot indicate the degree of aperture opening, hence cannot be used to determine that the valveis opening sufficiently far to by-pass water in great enough quantity to maintain correctpressure.The lamp will remain lighted until the chum valve is completely closed.When the pump is operating and supplying one or more lines ofhose at the correct pressure,and the relief valve is set for that pressure, he control valve piston will remain in a normaloperating, or closed position, as ong as the playpipes are open. At this point the controllingspring pressure s equal to the pump dischargepressure.

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CEN11RIFUGAL FIRE PUMP

The instant that one or more playpipes are closed, the pressureon the discharge side of thepump exceeds he pressureexerted by the controlling spring, and the control valve opens.Although water at pump dischargepressure s now acting upon both ends of the churn valve,the churn valve opens oward the discharge side of the pump becauseof the greater totalforce exerted on the larger face. With the churn valve open, water flows from the dischargeside to the suction side of the pump, thereby reducing the discharge pressure o the pressurefor which the relief valve is set which is equal to the controlling spring pressure.With thedischarge pressureagain equaling the controlling spring pressure, he control valve movesback to the normal operating or closed position, blocking off the passage o the large end ofthe churn valve and stopping the flow of water to that chamber. This holds the churn valve ina partially open position to maintain the pressure or which the relief valve is set. When theplaypipes are reopened, he pump dischargepressureacting against the control valve isreduced. This allows the control spring pressure o close the control valve and drain thepressure etained in the water chamber at the large end of the churn valve. Pump pressureacting upon the small end of the churn valve then causes he churn valve to close and theflow between the discharge and suction sides of the pump is stopped. The pump pressureagain equals he controlling spring pressure,and the control valve closes, returning to thenormal operation positicn.Pumping situations are varied; therefore, various operating pressuresand quantity flows arerequired to suit them and the demandsmade upon the relief valve are also varied. In order toprovide complete control over pressurechangeswhen pumping in situations where playpipesare frequently being closed and opened without notice to the pump operator, such as nfirefighting, drill, etc.; the relief valve and throttle must be properly set. To set the reliefvalve so its operation becomesautomatic and effective for the given situation, first thecontrol hard wheel must be turned clockwise a sufficient number of turns so that the springpressurewill be greater than the desired pump pressure; second he playpipe(s) on the hoseline(s) being supplied must be open; and, third the throttle must be carefully adjusted oachieve the correct pump pressure.With these criteria met, then:Turn control handwheel counterclockwise until pump pressure drops. The control handwheel should be turned counterclockwise until the pump pressure starts to drop; the reliefvalve pilot light should come on. Then, stop turning in that direction and

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Turn control valve clockwise until desired pump pressure s reached.This should be doneslowly until the desired pump pressure s again reached.The relief valve pilot light should gooff. Unless pumping conditions change, he relief valve requires no further attention.Adjustments in pump pressureshould not be made with the relief valve. If a pump pressurehigher than the one being used s desired; turn control hand wheel clockwise a sufficientdistance so that the spring pressurewill be greater han the desired higher pump pressure,raise the pump pressurewith the throttle, and reset he relief valve. If a pump pressure owerthan the one being used s desired; ower the pump pressurewith the throttle and reset herelief valve.If the relief valve is mechanically sound, the steps of setting should insure that when the pipeis closed, the chum valve will open far enough o chum that quantity of water which wasformerly being discharged, and no increase n pump pressurewill occur. When the pipe isreopened, he chum valve will close, and pump pressurewill remain the same. Of course, aswith any mechanical device having maximum performance evels, there is a limit to theopening size of the chum valve, and hence a limit as to the amount of water that can passthrough it. Therefore, if a pump is discharging a quantity of water that is near the totalcapacity of the pump, and the pi}Jesare then shut off, the chum valve cannot open far enoughto maintain proper pump pressure.There are times when it is impossible to set the relief valve with water being discharged; orinstance. f the company is still attempting to locate the fire inside a building, an operator ofpumping apparatuscannot ask that the playpipe be opened ong enough for him to set therelief valve. There may be other times when the water flow from an open pipe may be toosmall to warrant concern over maintaining constant pressure,such as n wetting down withthe small line. Under these circumstances, he relief valve can be set only to prevent thepump pressure rom exceeding he desired pressure.To set the relief valve, with no waterflowing, and accomplish the protection against higher pressures, irst the control hand wheelmust be turned clockwise a sufficient number of turns so that the spring pressurewill begreater than the desired pump pressureand second he throttle must be carefully adjusted oachieve he correct pump pressure.With these criteria met, then:Turn control hand wheel counterclockwise until pump pressuredrops. The control handwheel should be turned counterclockwise until the pump pressure starts to drop; the reliefvalve pilot light should come on. Then, stop turning in that direction and

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CENTRIFUGAL F IRE PUMP

Turn control hand wheel clockwise until desired pressure s reached.This should be doneslowly until the desired pump pressure s again reached.The relief valve pilot light should gooff.If these steps of setting are done without water flowing, then when the playpipe is opened,the pump pressurewill decrease.When the playpipe is closed, the relief valve will insure thatpump pressuredoes not rise above the pressure or which the relief valve is set.The relief valve can also be preset to a particular pressure,and later when the pump is used,the relief valve will afford protection against most increases n pump pressureswhile gettingin service on the fire ground. The preset relief valve will assist he wagon driver in thechangeover rom booster tank to supply line. It will also assist he pumper driver in getting inservice and operating until the need for a particular quantity of water is established.In presetting the relief valve to a partict:lar pressure t makes no difference whether water isflowing or not. One may choose o use any discharge ane available, or may choose o directthe flow from the small line into the booster tank, or may choose o keep all discharge gatesclosed. This would allow presetting the relief valve at company quarters, after pumping andbefore leaving the fireground, after drills, etc., in preparation for the next anticiproted umpsituation.What is being accomplished s the establishmentof a balance between a given pump pressureand the spring pressureagainst he control valve piston. To preset the relief valve, first thecontrol hand wheel must be turned clockwise a sufficient number of turns so that the springpressurewill then be greater than the ultimate preset pressure; and second he throttle mustbe carefully adjusted to achieve he desired pump pressure preset pressure).With these criteria met, then:Turn control hand wheel counterclockwise until pump pressuredrops. The control handwheel should be turned counterclockwise until the pump pressure starts to drop; the reliefvalve pilot light should come on. Then, stop turning in that direction andTurn control hand wheel clockwise until desired pump pressure s reached.This should bedone slowly until the desired pump pressure s again reached.The relief valve pilot lightshould go off.Upon completing the steps of presetting the relief valve, the pump is shut down and theapparatusmade ready for future service.

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If these steps of presetting are correctly done, the next time the pump is used and the throttlecontrol advanced o develop pump pressure o coincide with the preset relief valve pressure,the relief valve should afford protection against most increases n pump pressure.There are no provisions for company level maintenanceof relief valves. Frequent operationof the relief valve, so that all moving parts are set n motion, assistsgreatly in keeping itoperative. Any pump part is susceptible o rust scale ncrustation, and if the chum valve andcontrol valve are allowed to remain in one position for lengthy periods of time a coating maybuild up, tending to limit the normal travel of said parts.Checking the operation of the relief valve during fire fighting operations by closing gatesorby attempting to increase he pump pressureby throttle advancementshould not be done.These hings interfere with the proper supply to the hose ines and can endanger hefirefighters holding the playpipes. Increasing the pump pressurewith the throttle increasesthe flow of water through the chum valve and does not give an accurate ndication of thecondition of the relief valve.Testing of the relief valve, when there is evidence t is not working properly, can beaccomplished as fo;lows:Place the pump in service supplying a line with the playpipe open. Use a pump pressureof atleast 50 psi over the hydrant or intake pressure.A discharge of at least 100 gpm will providea good test. Set the relief valve properly. Close the playpipe. The relief valve should hold thepump pressurewith not more than an increaseof 30 psi. Open the playpipe. The pumppressureshould not drop below the point of the original psi. If the increase n pressure sgreater han 30 psi when the pipe is closed, or if the pump pressure drops below the originalpsi when the pipe is opened, t indicates that the relief valve is not functioning properly.If the relief valve is not functioning properly, repeat he test, taking special care in all steps.Repeating he test several times will frequently correct the difficulty .Causing the relief valveto work several times will sometimes ncrease he accuracy of the relief valve operations. fcontinued attempts to make the relief valve work are unsuccessful, he Fleet MaintenanceDivision should be notified.

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LUBRICATIONThere are no greaseconnections provided for the main pump shaft bearings. Pump packing isprovided at the pump shaft where it leaves he pump casing. It takes a tight fit between thepump shaft and the casing and prevents eakage of air when priming the pump. The pumppackings are lubricated by water; therefore, a small amount of water should run from thesepackings when the pump is in operation. Excessive eakage of the packing will cause roublein getting water from draft and should be reported to Fleet Maintenance. Do not attempt tomake any adjustment of the packing. It shall be taken into consideration that the pumppackings are susceptible o damage rom being overheatedwhen the pump is not dischargingwater and continues to chum. This situation can often causedamage o the packings withoutany noticeable heat build up on the exterior of the pump casing ( 6" intake blind cap, or the2 Y2 piping at the in line valves). To avoid this damage o the packings open slightly thetank fill valve to-circulate water, a discharge gate or open a play pipe to allow water to flowfrom the pump.The oil in the pump transmission shall be kept between the high and low level mark on thebayonet gauge, using S.A.E. 90 weight gear oil. Fleet Maintenance will maintain the above.The pump bearings, drive unit bearings and all gears are supplied with oil from the drive unithousing. Too much oil or too heavy an oil will result in unnecessary oss ofpower andunnecessarilyhigh oil temperature.These tems shall be checked and maintained by FleetMaintenance.

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Chapter II the Centrifugal Fire Pump

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