A.vary their speed according to temperature and load
B.start and come up to speed before air compression begins
C.change speed according to overload demands
D.reduce compressed air charge density
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A.radiation
B.conduction
C.convection
D.condo-radiation
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
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
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When the steering gear is in operation, you should （）.
One cause of high head pressure occurring in a refrigeration system can be （）.
If the head pressure of a reciprocating refrigeration compressor is excessive, （）.
A salinity indicator is used to determine the （）.
A pressure drop through the refrigerant liquid line may cause （）.
Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.
The rate of heat transfer between the hot and cold fluids passing through a shell-and-tube type heat exchanger will （）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
The usual symptoms of cavitation in a centrifugal pump is （）.