Thermostatic expansion valves can be adjusted for （）.

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

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

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

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

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

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