單項(xiàng)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


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1.單項(xiàng)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

2.單項(xiàng)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

3.單項(xiàng)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

4.單項(xiàng)選擇題When a refrigeration compressor motor fails to start, the FIRST thing that should be checked for is a （）.

A.loose expansion valve control bulb
B.low differential setting on the H-Pcutout
C.blown fuse in the motor circuit
D.faulty suction pressure regulator

5.單項(xiàng)選擇題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