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

If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.

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

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

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

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 （）.

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

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

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