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單項(xiàng)選擇題

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

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

單項(xiàng)選擇題

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