默认题库 - 船舶辅助机械

单选题

In order to properly remove air from the casing of a centrifugal pump when starting, the pump should have a （）.

A. positive head
B. negative suction head
C. mechanical seal
D. vent valve attached to the casing at the top of the volute

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单选题

（）are used to ensure that ships don’t discharge oil when pumping out oily water from any oil contaminated space.

A. Boiler
B. Incinerator
C. Oily water separator
D. Sewage treatment unit

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单选题

Which of the problems listed represents the major difficulty encountered with thermal expansion valve operation?（）

A. Lube oil passing through the system
B. Moisture or foreign matter collecting at the valve seat and orifice
C. Variable spring tension caused by the changing temperature
D. Frost on the liquid line

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单选题

Excessive oil foaming in the crankcase of a refrigeration compressor is most likely to occur（） when the compressor.

A. has continuously for a long period
B. suction pressure is below normal
C. oil level is below normal
D. starts after a long idle period

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单选题

Which of the following problems could cause air to blow out through the inlet air filter of a running compressor?（）

A. Excessive compression in the cylinder
B. A broken intake valve
C. A dirty inlet filter element
D. An improperly adjusted discharge valve

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单选题

Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）

A. Thermal expansion valve frozen open
B. Suction gas heat exchanger bypassed
Condenser clogged or fouled
D. High pressure cutout switch inoperative

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单选题

When distilling sea water the cooling water discharging from the distiller is fed back to evaporator as feed water （）.

A. to decrease scale formation
B. for better cooling effect
C. for more economical purpose
D. to raise vacuum

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单选题

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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单选题

If a reciprocating air compressor has a knock occurring in frequency with its operating RPM, the cause is probably （）.

A. misalignment or worn main bearings
B. insufficient cylinder lubrication
C. defective or poorly fitted valves
D. all of the above

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单选题

Because of the reduced （） in the vacuum boiling evaporator, some of the sea water boils as it flows through the tubes.

A. temperature
B. water level
C. pressure
D. rate of flow

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