單項(xiàng)選擇題

Sealing in pump shaft is achieved by means of the （）.

A.gasket
B.packing
C.washer
D.spring

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單項(xiàng)選擇題

（） is the breakdown of surface tension between oil droplets in an oil water mixture which causes them to join and increase in size.

A.Wear
B.Contaminating
C.Coalescence
D.Coarse separating

單項(xiàng)選擇題

Centrifugal pumps are popular because they are very simple in construction,and produce smooth, constant, （） discharge.

A.non-pulsating
B.pulsating
C.positive
D.non-positive