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
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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）
Which of the following pumps will build up a bursting pressure or stall their motors if the discharge valves are closed?（）
(1) gear
(2) centrifugal
(3) screw
A.（1）and（2）
B.（1），（2）and（3）
C.（1）and（3）
D.（2）and（3）
A.providing the impeller with balancing holes
B.the use of symmetrical impeller
C.neither A nor B
D.either A or B
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If the head pressure of a reciprocating refrigeration compressor is excessive, （）.
A salinity indicator is used to determine the （）.
The major source of chemical contaminants in hydraulic fluid is （）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
Thermostatic expansion valves can be adjusted for （）.
If the viscosity of the liquid being transferred remains constant as the discharge pressure increases, the rotary pump （）.
The usual symptoms of cavitation in a centrifugal pump is （）.
The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
The rate of heat transfer between the hot and cold fluids passing through a shell-and-tube type heat exchanger will （）.
Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.