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

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

A salinity indicator is used to determine the （）.

Low compressor head pressure in a refrigeration system can be caused by（）.

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

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

The usual symptoms of cavitation in a centrifugal pump is （）.

The rate of heat transfer between the hot and cold fluids passing through a shell-and-tube type heat exchanger will （）.

Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.

On tank vessels equipped with power operated cargo tank valves, the type of power operator most commonly used is （）.