单项选择题
Which of the listed pumps is NOT a positive displacement pump?（）
A.Centrifugal
B.Reciprocating
C.Gear
D.Rotary
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相关考题
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单项选择题
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 -
单项选择题
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 -
单项选择题
Low compressor head pressure in a refrigeration system can be caused by（）.
A.insufficient condenser cooling water
B.excessive condenser cooling water
C.air in the refrigeration system
D.excessive refrigerant in the system
