单选题A centrifugal impeller consists of a number of vanes curving （） from the direction of rotation.AbackwardsBforwardsCupwardDdownwards
单选题
A centrifugal impeller consists of a number of vanes curving （） from the direction of rotation.
A
backwards
B
forwards
C
upward
D
downwards
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第二组Displacement pumps are those where the volume of the pump chamber is alternately increased to draw the liquid in from the suction pipe and then decreased to force the liquid out into the delivery pipe. Centrifugal pumps are those wherein an impeller rotating at high speed throws the liquid by centrifugal force from the center to the periphery of the impeller where the liquid is discharged through the delivery outlet.Gear pump consists of two or more meshing gears (spur, single or double helical teeth) enclosed m a close-fitted housing. These are used extensively for pumping fuel oil, lubricating oil and hydraulic oil. When gears are unmeshed on the inlet side, a pressure drop occurs that helps the atmospheric pressure acting on the surface of the oil in the reservoir to force it up the pipe to fill the void, the oil is then transferred around the periphery of the pump housing. As the gear teeth mesh again on the outlet side, they form. a seal that prevents oil from backing up to the inlet, the oil in the void is then be forced out into the discharge line.All vane pumps have a rotor driven within a ring (cam ring) by a drive shaft coupled to a prime mover. A cylindrical rotor with sliding vanes, generally in radial slots, rotates within the ring. The center of the rotor is offset from the center of the ring. In a simple vane pump, as the rotor turns, the vanes are forced outward against the inner surface of the cam ring by centrifugal force. This outward radial movement of the vanes and turning of the rotor causes the chamber between the vanes to increase as the vanes pass further away from the inlet port. This increase in volume results in a lowering of pressure until the atmospheric pressure is sufficient to force oil from the reservoir into the inlet chamber. Oil from the inlet is swept away by the vanes toward the outlet port through a decreasing series of chambers until it is forced through the outlet port. A vane pump of balanced design has an elliptical cam ring so that two pumping chambers are formed. This pump is in hydraulically balance, since the two intake and two outlet ports are diametrically opposed to each other. Therefore the side loads exerted on the rotor cancel out, thereby increasing bearing lift and permitting high operating pressure.According to the last sentence of paragraph 1, from where the liquid is discharged through the delivery outlet?A.from the eye of the impellerB.from passage of impellerC.from the periphery of the impellerD.from the impeller
It is possible to mount a double suction centrifugal pump impeller with the vanes facing in the wrong direction. This would cause the pump ______.A.head capacity to improveB.discharge to be reversedC.efficiency to decreaseD.slippage to decrease
A centrifugal pump may fail to deliver water when first started if the ______.A.water seal pipe is pluggedB.pump is not primedC.seal ring is properly locatedD.impeller is flooded
What causes cavitation in a centrifugal pump ________．A.Vapor pockets in the flow streamB.Rough impeller surfacesC.Worn wearing ringsD.Heavy fluid in the flow stream
单选题Which of the following statements is correct with regards to the operation of a centrifugal cargo pump?（）AOil is discharged from the impeller through the outletBGravity causes the oil to flow toward the dischargeCThe self-priming feature of the centrifugal pump enables it to draw its own suction as it startsDThe discharge capacity varies directly with the speed of the impeller
单选题In a turbocharger, inlet air velocity is increased in the（）.Ainlet nozzle ringBstationary diffuser passagesCcompressor outlet voluteDrotating impeller vanes
单选题A variable displacement system of hydraulic drives consists of （）.Aa variable displacement axial piston pumpBa constant displacement axial piston pumpCa reciprocating piston pumpDa centrifugal pump
单选题With reference to a rotary vane steering gear system, which one of the following statements is true?（）AThe three moving vanes and the three fixed vanes form three pressure chambersBThe three moving vanes and the three fixed vanes form six pressure chambersCThe three moving vanes and the three fixed vanes form nine pressure chambersDThe three moving vanes and the three fixed vanes form twelve pressure chambers
单选题A double suction centrifugal pump impeller has been installed in the reverse direction, and will （）.Ahave a greater head capacityBoperate with increased impeller efficiencyCdischarge through the suction side of the pump casingDrequire more power to run the shaft
单选题A multistage centrifugal pump can be BEST described as having （）.Atwo or more impellers housed together in one casing and mounted on a single shaftBa single stepped impeller mounted in a progressively staged casingCa large radial clearance between the impeller and casing to prevent overheating due toDan increase in the discharge velocity of the liquid with a corresponding decrease in pressure through the stages
单选题Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.AcavitationBelectrolysisCabrasionDcorrosion
单选题Increasing the speed of a centrifugal pump will result in an increase in its capacity Another means of increasing the capacity of a centrifugal pump is to increase the （）.Adiameter of the discharge piping, with all other factors remaining the sameBdiameter of the suction piping, with all other factors remaining the sameCwidth of the impeller onlyDdiameter of the impeller
单选题Increasing the speed of a centrifugal pump will result in an increase in its capacity in its capacityAnother means of increasing the capacity pump is to increase the（）Adiameter of the discharge piping, with all other factors remaining the sameBdiameter of the suction piping, with all other factors remaining the sameCwidth of the impeller onlyDdiameter of the impeller
单选题One of the main functions of wearing rings, as used in a centrifugal pump, is to （）.Amaintain radial alignment between the pump impeller and casingBabsorb all impeller shaft end thrustCprevent water leakage to the atmosphereDprevent wear of the pump casing and/or impeller
单选题For optimum results, centrifugal purification of heavy fuel oil should be accomplished with the fuel at the lowest practicable（）AthroughputBadditive percentCcetane numberDTBN number
单选题Attempts are made to eliminate axial thrust in centrifugal pump by （）.Aproviding the impeller with balancing holesBthe use of symmetrical impellerCneither A nor BDeither A or B
单选题To absorb the wear resulting from impeller rotation and abrasives in the liquid, a centrifugal pump is usually fitted with （）.Alantern ringsBbearingsCeasing volutesDwearing rings
单选题It is possible to mount a double suction centrifugal pump impeller with the vanes facing in the wrong directionThis would cause the pump （）.Ahead capacity to improveBdischarge to be reversedCefficiency to decreaseDslippage to decrease
单选题Which of the listed statements is correct concerning the starting of centrifugal pumps?（）AThey should always be started with the discharge valve closedBThey should always be started with the discharge valve openedCA priming pump is always required to flood the impeller suctionDThey should always be started with the sealing line valves closed
单选题The basic function of the centrifugal pump impeller is to （）.Adirectly increase the pressure of the liquid being pumpedBdirectly increase the velocity of the liquid being pumpedCconvert the potential energy of the liquid to kinetic energyDseparate air from the liquid being pumped
单选题A centrifugal pump produces the required pressure energy by means of a rotating （） provided with vanes.ApropellerBimpellerCcircumferenceDscrew
单选题To maintain design discharge pressure from a centrifugal pump, the design clearance must be maintained between the （）.Ashaft and impellerBmotor and pump shaftCcasing and impeller wearing ringsDlantern ring and impeller
单选题Which features of a centrifugal pump reduce the need for renewing worn impellers and pump casings?（）AClose radial clearance between impeller hub and casingBLow rotational speed of impellerCRemovable end plateDReplaceable impeller and casing wearing rings
单选题The discharge head of a centrifugal pump will vary directly with the （）.Achange in impeller diameterBsquare of the impeller diameterCcube of the impeller diameterDimpeller efficiency for large changes in the size of the impeller
单选题The discharge rate or capacity of a centrifugal pump will vary directly as the （）.Achange in the impeller diameterBsquare of the impeller radiusCcube of the impeller diameterDimpeller efficiency for large changes in its size
单选题Centrifugal pumps, however, can be designed with a number of impellers （） to attain a large amount of liquid.Ain seriesBin parallelCassembledDtogether
单选题A centrifugal pump vibrates excessively during operationUpon disassembling the pump it is found that the impeller is out of balanceWithout an available spare, you should （）.Adrill holes through the heavy side of the impeller until it balancesBweld counterweights to the light side of the impellerCremove metal from the heavy side by machining in a latheDacid wash and serape the heavy side until it balances