单项选择题
A.cause a loss of the liquid seal B.create a vapor lock in the liquid receiver C.collect in the condenser D.cause foaming of the oil in the crankcase
Pressure in an operating hydraulic system is developed ...
单项选择题Pressure in an operating hydraulic system is developed （）.
A.only by the pump as its primary function B.by resistance to the fluid flow through the system C.by the thermal input to the systems fluid D.solely by the charge applied by the accumulators
If a large difference exists between the compressor dis...
单项选择题If a large difference exists between the compressor discharge pressure and the pressure corresponding to the existing condensing temperature in a refrigeration system, you should（）.
A.increase the flow of the cooling water through the condenser B.adjust the high pressure cutout to maintain the desired pressure C.open the hot gas bypass temporarily to reduce capacity D.purge non-condensable gases to reduce the excess pressure
Which of the following statements concerning butterfly ...
单项选择题Which of the following statements concerning butterfly valves is correct?（）
A.Special tools are required for lapping or grinding B.It is impossible to throttle flow with a butterfly valve C.To close the valve, it is only necessary to turn the handle a quarter of a turn D.The butterfly valve should never be used in a freshwater system
