單項選擇題The accumulation of air and other non-condensable gases in a refrigeration system will （）.

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


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1.單項選擇題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

2.單項選擇題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

3.單項選擇題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

4.單項選擇題The simplest method to use for determining if a centrifugal pump is operating as designed, is to （）.

A.closely observe the pump discharge temperature
B.close off the discharge valve, and watch for a rise in pressure
C.momentarily close off the suction valve, and watch for a rise in pressure
D.use a clamp on ammeter and compare the readings to past records

5.單項選擇題Air compressors are equipped with unloading systems for the purpose of（）.

A.removing all but the frictional load during starting
B.relieving intercoolers of high temperature buildups
C.providing high starting torque in the drive motor
D.seating valve plates during compressor shutdown