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）
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A.providing the impeller with balancing holes
B.the use of symmetrical impeller
C.neither A nor B
D.either A or B
A.throttling the pressure line
B.changing the speed of the rotor
C.either A or B
D.None of the above is true
Which of the following pumps are self-priming, and can deal with liquid from a level below the pump（）
(1) ejector
(2) screw
(3) centrifugal
A.(1)only
B.(1)and(2)
C.(1),(2)and(3)
D.(2)and(3)
A.centrifugal
B.plunger
C.injector
D.water
A.discharges into a gradually widening channel
B.has stationary diffuser vanes
C.produces no kinetic energy
D.All of the above are true
最新試題
When the steering gear is in operation, you should （）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.
An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.
A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.
Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
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The general purpose of a heat exchanger is to （）.
The output volume of a positive fixed displacement pump can be changed only by （）.