单项选择题

Most solenoid valves are actuated by （）.

A.a spring
B.an electromagnet
C.the force of gravity
D.refrigerant pressure

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单项选择题

When normal operating pressure is applied to the hydraulic oil used in a high-pressure system, the oil （）.

A.viscosity will decrease
B.volume will increase
C.volume will decrease
D.pour point will be reduced

单项选择题

If the refrigeration compressor crankcase is sweating, the cause may be due to （）.

A.a shortage of refrigerant
B.the compressor running continuously
C.liquid refrigerant returning to the compressor
D.the compressor short cycling on the high pressure cutout

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The primary reason low pressure evaporators produce distillate more efficiently, and with less scale formation, than high pressure evaporators is （）.

A.evaporation is accomplished in a vacuum
B.due to the higher temperature of the incoming feed
C.due to the latent heat of evaporation principle
D.evaporation in a submerged medium produces more distillate