单项选择题

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

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

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单项选择题

If the head pressure of a reciprocating refrigeration compressor is excessive, （）.

A.the relief valve should open before the high pressure cutout
B.the relief valve should open and allow the excess refrigerant to flow to the receiver
C.the high pressure cutout switch should operate before the relief valve opens
D.you should close in on the suction valve

单项选择题

A salinity indicator is used to determine the （）.

A.cause of salt contamination
B.location of salt water contamination
C.chemical makeup of feed-water
D.level of alkalinity in condensate

单项选择题

An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.

A.restriction in refrigerant piping
B.air and non-condensable gases in the condenser
C.water in the refrigerant
D.flooding back of liquid refrigerant from the evaporator