A.used in either the fully dosed or fully opened position
B.installed with the stem down
C.used for steam service only
D.used to throttle or regulate the flow of liquid
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A.Radiation
B.Conduction
C.Natural convection
D.All of the above
A.A gate valve
B.A globe valve
C.Any check valve
D.Any needle valve
A.a shortage of compressor oil
B.warm food in the refrigerator
C.excessive condenser cooling water
D.a shortage of refrigerant
A.molecular fluid vibration
B.energy losses
C.wide pressure variations
D.mechanical damage to control valves
A.Keeps the refrigerated space cooler
B.Reduces the efficiency of the plant
C.Takes the load off the compressor
D.Has no affect on the system
最新試題
One cause of high head pressure occurring in a refrigeration system can be （）.
Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）
If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.
If the head pressure of a reciprocating refrigeration compressor is excessive, （）.
The usual symptoms of cavitation in a centrifugal pump is （）.
A salinity indicator is used to determine the （）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
Which of the following statements is correct concerning heat transfer?（）
If the relief valve on the discharge side of a hydraulic pump lifts, the cause could be （）.
The rate of heat transfer from a hot region to a cold region is affected most by the （）.