Which of the following pumps are self-priming, and can deal with liquid from a level below the pump? （）
(1) reciprocating
(2) rotary
(3) centrifugal
A.（1）only
B.（1）and（2）
C.（1），（2）and（3）
D.（2）and（3）
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A.increased；decreased
B.decreased；increased
C.decreased；decreased
D.increased；increased
A.kg
B.MPa
C.mH20
D.None of the above
Which of the following are components of a mechanical seal? （）
(1) stationary ring
(2) rotational ring
(3) packing
(4)spring
A.(1), (2) and (3)
B.(1), (2) and (4)
C.(2), (3) and (4)
D.None of the above
A.variable stroke pumps
B.multistage pumps
C.positive displacement pumps
D.triple-ported pumps
A.mixed-flow pump
B.axial-flow pump
C.centrifugal pump
D.displacement pump
最新試題
If the relief valve on the discharge side of a hydraulic pump lifts, the cause could be （）.
A grease gun is generally used to lubricate a （）.
Which of the following statements is correct concerning heat transfer?（）
The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.
A pressure drop through the refrigerant liquid line may cause （）.
Which of the listed pumps is NOT a positive displacement pump?（）
Who is responsible for ensuring that someone is assigned to close the watertight doors in an emergency?（）
If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.
The output volume of a positive fixed displacement pump can be changed only by （）.
Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）