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

An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.

A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.

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

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?（）

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

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 （）.

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