单项选择题

The purpose of the wearing rings used in a centrifugal pump is to （）.

A.prevent an internal explosion in the pump when it is overheated
B.enable a visual inspection of the pump while it is running
C.insure a proper alignment of the pump coupling to the driver
D.accommodate for friction between the impeller and the easing

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单项选择题

The lowest temperature required to cause self-sustained combustion of a substance independent of any outside source of ignition is called （）.

A.explosive range
B.flash point
C.ignition temperature
D.combustion temperature

单项选择题

If a refrigeration compressor will not start, the reason may be （）.

A.the pressure regulating valve is not closing
B.an excessive lack of refrigerant in the system
C.badly leaking discharge valves
D.worn piston rings

单项选择题

Which of the following statements describes the relationship between flash point and ignition temperature?（）

A.Both are higher than normal burning temperatures
B.The flash point is always higher
C.The ignition temperature is always higher
D.They are not necessarily related