單項選擇題A vane pump belongs to （） according to its working principle.

A.reciprocating pump
B.positive displacement pump
C.centrifugal pump
D.centripetal pump


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1.單項選擇題An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.

A.restriction in refrigerant piping
B.air and non-condensable gases in the condenser
C.water in the refrigerant
D.flooding back of liquid refrigerant from the evaporator

2.單項選擇題One cause of high head pressure occurring in a refrigeration system can be （）.

A.insufficient cooling water flow to the condenser
B.a low refrigerant charge in the system
C.the liquid valve is open too much
D.high evaporator superheat

3.單項選擇題Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.

A.cavitation
B.electrolysis
C.abrasion
D.corrosion

5.單項選擇題A salinity indicator is used to determine the （）.

A.cause of salt contamination
B.location of salt water contamination
C.chemical makeup of feed-water
D.level of alkalinity in condensate

6.單項選擇題If you are given the job of adding hydraulic fluid to a mooring winch, and are not certain as to the type of fluid to use, you should （）.

A.add fluid that is the same color as the fluid in the reservoir
B.add turbine oil because it is always a good substitute
C.add any oil that has the same viscosity as the hydraulic fluid
D.check the winch manufacturers instruction book

7.單項選擇題Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?（）

A.A shortage of liquid refrigerant
B.Excessive frost on the evaporator
C.Excessive condenser cooling water
D.Insufficient condenser cooling water flow

8.單項選擇題If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.

A.refrigerant overcharge
B.overfeeding by the expansion valve
C.a restricted suction strainer
D.due to short cycling of the compressor

9.單項選擇題Thermostatic expansion valves can be adjusted for （）.

A.suction pressure only
B.head pressure only
C.superheat only
D.suction pressure and box temperature

10.單項選擇題The output volume of a positive fixed displacement pump can be changed only by （）.

A.changing the angle of the tilting plate
B.changing the speed of the pump
C.moving the slide block and rotor
D.moving the shaft trunnion block