The output volume of a positive fixed displacement pump can be changed only by （）.

单项选择题An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.

A.oil foaming in the compressor
B.higher than normal suction and discharge pressures with a higher box temperature
C.higher than normal discharge pressure with a normal box temperature
D.the compressor to run continuously

单项选择题When the steering gear is in operation, you should （）.

A.check hydraulic oil levels every hour
B.check the rams for overheating
C.check for excessive oil leakage from rams
D.drain water from telemotor cylinders each watch

单项选择题The oil in a cargo winch gear box should be sampled periodically to （）.

A.prevent the gear box from leaking
B.prevent the oil from becoming inflammable
C.make sure it has not become contaminated
D.make sure the motor bearings are lubricated

单项选择题A spur gear pump should be operated with the discharge valves （）.

A.slightly opened
B.throttled
C.fully opened
D.halfway opened

单项选择题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 speed
B.increase the size of the cardent assembly
C.reduce wearing ring clearances
D.change the pump to a "close coupled" arrangement