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 （）.

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• The purpose of the wearing rings used in a centrifugal pump is to （）.

  A . prevent an internal explosion in the pump when it is overheated B . enable a visual inspection of the pump while it is running C . insure a proper alignment of the pump coupling to the driver D . accommodate for friction between the impeller and the easing

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• It is possible to mount a double suction centrifugal pump impeller with the vanes facing in the wrong directionThis would cause the pump （）.

  A . head capacity to improve B . discharge to be reversed C . efficiency to decrease D . slippage to decrease

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• The discharge rate or capacity of a centrifugal pump will vary directly as the （）.

  A . change in the impeller diameter B . square of the impeller radius C . cube of the impeller diameter D . impeller efficiency for large changes in its size

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• Which of the following actions should be taken if during a routine maintenance inspection of a centrifugal pump, localized scoring on a pump shaft sleeve is detected?（）

  A . Correct the cause of the scoring and repair the sleeve or replace with a new one B . Reassemble the unit and provide more water leak off for proper lubrication C . Check for parallel alignment of the sleeve radial faces to the sleeve bores D . Reassemble the unit and adjust the governor to obtain a slower speed

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• The usual symptoms of cavitation in a centrifugal pump is （）.

  A . noise and vibration B . an increase in discharge pressure C . an increase in suction pressure D . lifting of the relief valve

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• Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.

  A . cavitation B . electrolysis C . abrasion D . corrosio

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• A multistage centrifugal pump can be BEST described as having （）.

  A . two or more impellers housed together in one casing and mounted on a single shaft B . a single stepped impeller mounted in a progressively staged casing C . a large radial clearance between the impeller and casing to prevent overheating due to D . an increase in the discharge velocity of the liquid with a corresponding decrease in pressure through the stage

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• A double suction centrifugal pump impeller has been installed in the reverse direction, and will （）.

  A . have a greater head capacity B . operate with increased impeller efficiency C . discharge through the suction side of the pump casing D . require more power to run the shaft

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• What is a function of the wearing rings used in most centrifugal pumps?（）

  A . Absorb erosion of high velocity discharge stream B . Seal pump shaft against entry of air C . Isolate the discharge side from the suction side D . Dampen the turbulent discharge flow

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• If the capacity of a centrifugal pump decreases gradually over a long period of time, you should replace the （）.

  A . packing gland B . mechanical seals C . lantern rings D . wearing ring

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• Which features of a centrifugal pump reduce the need for renewing worn impellers and pump casings?（）

  A . Close radial clearance between impeller hub and casing B . Low rotational speed of impeller C . Removable end plate D . Replaceable impeller and casing wearing ring

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• The function of a centrifugal pump double volute casing is to （）.

  A . reduce radial thrust to the impeller B . double the liquid velocity through the pump when compared to a single volute C . reduce hydraulic end thrust D . provide the effect of multi-staging

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• To maintain design discharge pressure from a centrifugal pump, the design clearance must be maintained between the （）.

  A . shaft and impeller B . motor and pump shaft C . casing and impeller wearing rings D . lantern ring and impeller

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• When installed for bilge pumping or ballast duty, centrifugal pumps require a （） to remove air from the suction pipe.

  A . air chamber B . head lank C . primer D . prime mover

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• What is a characteristic of all centrifugal cargo pumps? （）

  A . They are self-priming B . Decreasing the speed of rotation will decrease the discharge pressure C . Opening the discharge valve wider will increase the discharge pressure D . All of the above

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• When starting a centrifugal pump, the discharge valve should be （）.

  A . closed B . opened fully C . cracked open D . partly ope

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• The volute of centrifugal pump also acts as a diffuser converting （）into pressure head.

  A . mechanical energy B . heat energy C . potential energy D . kinetic head

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• A centrifugal pump can’t supply water after startingYou should check （）.

  A . priming water B . power supply C . packing gland D . bearing lubricatio

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• On modern ships, centrifugal pump with a self-primer has replaced reciprocating pump as bilge pump because（）

  A . centrifugal pump is cheaper than reciprocating pump B . the size of centrifugal pump with same capacity is smaller than that of reciprocating pump C . centrifugal pump makes maintenance easier than reciprocating pump does D . all of the above

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• A centrifugal bilge pump requires priming （）.

  A . primarily to lubricate the shaft seals B . due to the inability of this type of pump to lift water to cover the suction (eye) of the impeller C . to initially unload the pump by having its head pressure equal to discharge pressure D . in order to overcome the potential energy of water in the discharge line

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• The amount of fluid delivered by a centrifugal pump can be regulated by （）.

  A . throttling the pressure line B . changing the speed of the rotor C . either A or B D . None of the above is tree

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• The cleaned heated oil, after passing through the centrifuges, is to be pumped to a （）.

  A . settling tank B . service tank C . ballast tank D . drain tank

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• To operate a centrifugal fire pump at reduced capacity, you should （）.

  A . readjust the relief valve B . throttle the suction line C . throttle the discharge valve D . open the priming line

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• If you were operating a centrifugal water service pump with worn wearing rings, the （）.

  A . pump would be very noisy B . pump would vibrate excessively C . pump would develop insufficient flow D . stuffing box would leak excessively

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