單項選擇題

A swing check valve is used in a pipeline to （）.

A.maintain a preset pressure on the line
B.closely regulate the amount of flow
C.relieve excessive pressure on the line
D.allow flow in one direction only

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單項選擇題

Sluggish response or action of the hydraulic actuators may be a result of （）.

A.insufficient load
B.excessively high oil viscosity
C.relief-valve pressure setting too high
D.reservoir level being maintained two inches above normal

單項選擇題

A knocking sound from one cylinder of an operating air compressor indicates （）.

A.a defective or broken high pressure un-loader
B.a loose valve plate
C.excessive overload
D.no compression