单项选择题

Excessive oil foaming in the crankcase of a refrigeration compressor is most likely to occur（） when the compressor.

A.has continuously for a long period
B.suction pressure is below normal
C.oil level is below normal
D.starts after a long idle period

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单项选择题

Strainers are commonly used in hydraulic systems to （）.

A.protect the pump from fine soluble contaminants
B.prevent solid particles from entering the pump
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单项选择题

On which of the following heated surfaces of a flash type evaporator would you be more likely to find soft scale formation?（）

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B.Insulation of hot surfaces
C.Lubrication of moving parts
D.Elevation of cooler outlet temperatures