A.increase compressor discharge pressure on demand
B.increase compressor operating speed as necessary
C.allow the motor to turn the compressor opposed only by friction
D.reduce the compressor frictional load when starting
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A.Radiation
B.Conduction
C.Convection
D.Each of the above
A.Shortage of refrigerant oil
B.Slight shortage of refrigerant
C.Excessive condenser cooling water flow
D.Faulty expansion valve
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
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
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
最新试题
A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.
One cause of high head pressure occurring in a refrigeration system can be （）.
Low compressor head pressure in a refrigeration system can be caused by（）.
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
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（）.
Who is responsible for ensuring that someone is assigned to close the watertight doors in an emergency?（）
An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.
Thermostatic expansion valves can be adjusted for （）.