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

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

Who is responsible for ensuring that someone is assigned to close the watertight doors in an emergency?（）

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

If the relief valve on the discharge side of a hydraulic pump lifts, the cause could be （）.

Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.

Thermostatic expansion valves can be adjusted for （）.

The general purpose of a heat exchanger is to （）.