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

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

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

Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?（）

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

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

The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.

A salinity indicator is used to determine the （）.

When a refrigeration compressor has developed a high head pressure as a result of a refrigerant overcharge, you should （）.

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