A.discharge is continuous
B.it has no internal valves
C.upon accidental closing of discharge valve, excessive pressure will not build up
D.all of the above are true
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A.between the suction and discharge
B.below the liquid supply
C.above the liquid supply
D.any of the above
Which of the following pumps are self-priming, and can deal with liquid from a level below the pump? （）
(1) reciprocating
(2) vane
(3) gear
A.（1）only
B.（1）and（2）
C.（1），（2）and（3）
D.（2）and（3）
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）
A.increased；decreased
B.decreased；increased
C.decreased；decreased
D.increased；increased
A.kg
B.MPa
C.mH20
D.None of the above
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An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.
The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.
If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
A grease gun is generally used to lubricate a （）.
A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.
Which of the listed pumps is NOT a positive displacement pump?（）
The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
When the steering gear is in operation, you should （）.
If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.