單項選擇題

If a reciprocating air compressor has a knock occurring in frequency with its operating RPM, the cause is probably （）.

A.misalignment or worn main bearings
B.insufficient cylinder lubrication
C.defective or poorly fitted valves
D.all of the above

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單項選擇題

Why are removable sleeves installed on centrifugal pump shafts?（）

A.They make it easier to replace the pump shaft packing
B.They can be economically replaced as they wear out
C.They can be removed when it is necessary to lighten the weight of the pump
D.They increase the strength of the shaft

單項選擇題

In reference to air conditioning, when air attains the maximum amount of moisture it can hold at a specific temperature, it is said to be （）.

A.superheated
B.saturated
C.condensed
D.convected