单项选择题The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its ().

A.specific gravity
B.viscosity
C.S E number
D.hydrolytic stability


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1.单项选择题The major source of chemical contaminants in hydraulic fluid is ().

A.microscopic steel shavings
B.abrasive waste
C.anti-oxidant compounds
D.oxidation by-products

2.单项选择题If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will ().

A.increase the capacity of the coil
B.increase the superheat at the bulb
C.deliver more refrigerant to the coil
D.decrease the capacity of the coil

3.单项选择题Which of the listed pumps is NOT a positive displacement pump?()

A.Centrifugal
B.Reciprocating
C.Gear
D.Rotary

4.单项选择题Heavy wear in a particular area of the inner circumference of a packing ring may be caused by ().

A.a high suction head
B.rotating rings
C.badly worn bearings
D.a loose stuffing box gland

5.单项选择题A pressure drop through the refrigerant liquid line may cause ().

A.solenoid valve to seize
B.compressor to hunt
C.formation of flash gas in the liquid line
D.expansion valve to freeze open

6.单项选择题Low compressor head pressure in a refrigeration system can be caused by().

A.insufficient condenser cooling water
B.excessive condenser cooling water
C.air in the refrigeration system
D.excessive refrigerant in the system

7.单项选择题Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?()

A.Thermal expansion valve frozen open
B.Suction gas heat exchanger bypassed
C.Condenser clogged or fouled
D.High pressure cutout switch inoperative

8.单项选择题The usual symptoms of cavitation in a centrifugal pump is ().

A.noise and vibration
B.an increase in discharge pressure
C.an increase in suction pressure
D.lifting of the relief valve

9.单项选择题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

10.单项选择题The control mode in which the final control element is moved from one of two flexed positions to the other is known as ().

A.dead band action
B.neutral zone action
C.range
D.on-off action