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

If the viscosity of the liquid being transferred remains constant as the discharge pressure increases, the rotary pump （）.

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

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

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

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

An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.

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

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

A grease gun is generally used to lubricate a （）.