Which of the listed pumps is NOT a positive displacement pump?（）

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

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

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

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

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

Thermostatic expansion valves can be adjusted for （）.

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

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