单项选择题

The purpose of an air compressor unloading device is to （）

A.drain water from the air receiver
B.drain water from the cylinders
C.delay the compression process until the motor is up to speed
D.check pump alignment

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单项选择题

Personnel working with refrigeration systems, and subject to the exposure of refrigerants should wear （）.

A.face shield
B.a respirator
C.rubber gloves
D.an all purpose gas mask

单项选择题

To absorb the wear resulting from impeller rotation and abrasives in the liquid, a centrifugal pump is usually fitted with （）.

A.lantern rings
B.bearings
C.easing volutes
D.wearing rings

单项选择题

If the capacity of a centrifugal pump decreases gradually over a long period of time, you should replace the （）.

A.packing gland
B.mechanical seals
C.lantern rings
D.wearing rings