The output volume of a positive fixed displacement pump can be changed only by （）.

Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?（）

The major source of chemical contaminants in hydraulic fluid is （）.

One cause of high head pressure occurring in a refrigeration system can be （）.

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

If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.

A salinity indicator is used to determine the （）.

A pressure drop through the refrigerant liquid line may cause （）.

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

The rate of heat transfer from a hot region to a cold region is affected most by the （）.