A.reduce
B.rise
C.raise
D.fall
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A.increase discharge pressure
B.increase suction vacuum
C.develop pulsation flow
D.keep a steady rate of flow
A.slack enough to allow slight leakage of fluid
B.slightly clocked
C.brought up tight so as not to allow any leakage
D.fitted with a relief valve
A.Volute pump
B.Diffuser pump
C.Regenerative pump
D.All of the above
A.mixed-flow
B.axial-flow
C.centrifugal
D.displacement
Which of the following operating features do displacement pumps bear if they are working under no-cavitation condition?（）
(1) output is almost directly proportional to speed
(2) they are self-priming
(3) they will develop a discharged pressure equal to the resistance to be overcome, irrespective of speed
A.（1）and（2）
B.（2）and（3）
C.（1）and（3）
D.（1），（2）and（3）
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The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.
The general purpose of a heat exchanger is to （）.
A grease gun is generally used to lubricate a （）.
Which of the following statements is correct concerning heat transfer?（）
Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
Low compressor head pressure in a refrigeration system can be caused by（）.
When the steering gear is in operation, you should （）.