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單項選擇題

Which of the listed pumps is NOT a positive displacement pump?（）

A.Centrifugal
B.Reciprocating
C.Gear
D.Rotary

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單項選擇題

Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.

A.a high suction head
B.rotating rings
C.badly worn bearings
D.a loose stuffing box gland

單項選擇題

A pressure drop through the refrigerant liquid line may cause （）.

A.solenoid valve to seize
B.compressor to hunt
C.formation of flash gas in the liquid line
D.expansion valve to freeze open