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
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Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
One cause of high head pressure occurring in a refrigeration system can be （）.
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A salinity indicator is used to determine the （）.
The major source of chemical contaminants in hydraulic fluid is （）.
A salinity indicator is used to determine the （）.
The general purpose of a heat exchanger is to （）.
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