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单选题
Shaft sealing in a centrifugal pump can be effected by （）.
A
the mechanical seal
B
packed stuffing boxes
C
either A or B
D
neither A nor B
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单选题What is a function of the wearing rings used in most centrifugal pumps?（）A
Absorb erosion of high velocity discharge streamB
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to initially unload the pump by having its head pressure equal to discharge pressureD
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单选题Which pump installation would require an external source of sealing water?（）A
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set the relief valveB
check the lubrication systemC
vent the pump casingD
open the pump suction and discharge valves
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单选题One of the main functions of wearing rings, as used in a centrifugal pump, is to （）.A
maintain radial alignment between the pump impeller and casingB
absorb all impeller shaft end thrustC
prevent water leakage to the atmosphereD
prevent wear of the pump casing and/or impeller
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单选题The capacity of a centrifugal pump can be increased by the installation of a larger diameter impeller Another means of increasing the pump capacity is to （）.A
increase speedB
increase the size of the cardent assemblyC
reduce wearing ring clearancesD
change the pump to a close coupled arrangement
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单选题The purpose of the wearing rings used in a centrifugal pump is to （）.A
prevent an internal explosion in the pump when it is overheatedB
enable a visual inspection of the pump while it is runningC
insure a proper alignment of the pump coupling to the driverD
accommodate for friction between the impeller and the easing
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单选题Which of the listed statements is correct concerning the starting of centrifugal pumps?（）A
They should always be started with the discharge valve closedB
They should always be started with the discharge valve openedC
A priming pump is always required to flood the impeller suctionD
They should always be started with the sealing line valves closed
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单选题Excessive air leakage into the suction side of a centrifugal pump would be indicated by which of the following operational problems?（）A
The pump delivers full capacity when started, but gradually slackens off toan abnormally low flowB
The pump packing gland overheats after short operating periodsC
The motor over-current protective device continually shuts the pump downD
Pounding noises can be heard at the pump suction chest
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a compressed packing glandB
lantern tings between the packing ringsC
a liquid sealD
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changing the angle of the tilting plateB
changing the speed of the pumpC
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centrifugal pump is cheaper than reciprocating pumpB
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单选题A centrifugal pump can’t supply water after startingYou should check （）.A
priming waterB
power supplyC
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单选题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 oneB
Reassemble the unit and provide more water leak off for proper lubricationC
Check for parallel alignment of the sleeve radial faces to the sleeve boresD
Reassemble the unit and adjust the governor to obtain a slower speed
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单选题Which of the listed conditions can lead to cavitation气穴in a centrifugal pump?（）A
Vapor pockets formed in the suction flow streamB
Rough easing volute surfacesC
Worn wearing ringsD
Heavy fluid in the flow stream
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单选题Why are removable sleeves installed on centrifugal pump shafts?（）A
They make it easier to replace the pump shaft packingB
They can be economically replaced as they wear outC
They can be removed when it is necessary to lighten the weight of the pumpD
They increase the strength of the shaft
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