单项选择题
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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相关考题
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单项选择题
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） -
单项选择题
Attempts are made to eliminate axial thrust in centrifugal pump by （）.
A.providing the impeller with balancing holes
B.the use of symmetrical impeller
C.neither A nor B
D.either A or B -
单项选择题
The amount of fluid delivered by a gear pump can be regulated by （）.
A.throttling the pressure line
B.changing the speed of the rotor
C.either A or B
D.None of the above is true
