單項(xiàng)選擇題

A knocking sound emitted from an unloaded air compressor is probably caused by （）.

A.damaged intake valves
B.excessively tight mounting bolts
C.insufficient cylinder lubrication
D.a loose piston

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The refrigeration system low pressure cutout switch is actuated by （）.

A.an electric system manager
B.a sensing bulb at the tail coil of the evaporator
C.pressure changes in the suction line
D.failure of the king solenoid valve

單項(xiàng)選擇題

Hydraulic machinery failures are commonly caused by contamination of the hydraulic fluid and （）.

A.fluid friction
B.fluid turbulence
C.component misalignment
D.pressure surges