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【判断题】
发球是网球比赛中唯一可以直接由自己控制而不受对外界干扰的技术。A.
正确
B.
错误
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皮皮学刷刷变学霸
举一反三
【单选题】What is the function of wearing rings found on some centrifugal pumps ________．
A.
Absorb erosion of high velocity discharge stream
B.
Seal pump shaft against entry of air
C.
Isolate the outlet side from the inlet side
D.
Dampen the turbulent discharge flow
【判断题】Dynamic pumps are classified as centrifugal or axial. axial pumps operate on the principle of centrifugal force.
A.
正确
B.
错误
【单选题】Centrifugal pumps can be designed with a number of impellers _____ to attain a high final delivery pressure.
A.
in series
B.
in parallel
C.
either A or B
D.
None of the above is tree
【单选题】Centrifugal pumps have what advantage（s）over reciprocating pumps ________．
A.
They are less expensive
B.
They are smaller for equivalent pumping ability
C.
They pump more cargo in less time
D.
All of the above
【单选题】our long business relations and our amicable cooperation prospects, we suggest that you accept our terms.
A.
In that
B.
In view of
C.
For which
D.
Because of
【单选题】Which of the following pumps belongs to centrifugal pump?
A.
Piston pump
B.
Screw pump
C.
Diffuser pump
D.
Water-ring pump
【单选题】Most pump manufacturers recommend that the suction piping dimension for centrifugal pumps be _____.
A.
one size smaller than the pump suction nozzle
B.
the same size as the pump suction nozzle
C.
one size larger than the pump suction nozzle
D.
installed with a short radius elbow at the pump
【单选题】Which of the listed statements is correct concerning the starting of centrifugal pumps? .
A.
They should always be started with the discharge valve closed
B.
They should always be started with the discharge valve opened
C.
A priming pump is always required to flood the impeller suction
D.
They should always be started with the sealing line valves closed
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