A vacuum pump is a special device used to extract gas in a closed system to obtain a vacuum. At present, rotary vane vacuum pumps are commonly used in refrigeration maintenance work. It can pump the gas in the refrigeration system from 105Pa to below 1Pa.

The rotary vane vacuum pump uses a rotor with two sliding rotary vanes, which is eccentrically installed in the stator cavity. The outer circle of the rotor is tangent to the inner surface of the pump cavity. When the pump rotor rotates, the top of the rotary vane is kept in contact with the inner wall of the pump cavity by centrifugal force and spring pressure. The eccentric rotor drives the rotary vane to rotate in the stator cavity under the driving of the motor, so that the chamber at the air inlet gradually expands the volume. The air pressure drops and the gas is sucked in; at the same time, the volume of the chamber connected with the exhaust port gradually shrinks, and the air pressure rises. After reaching a certain pressure, the exhaust valve is opened to discharge the gas, so as to achieve the purpose of extracting the gas and obtaining a vacuum.

When using a vacuum pump to evacuate, in order to make the system achieve a higher degree of vacuum, the following points must be paid attention to:
(1) It must be ensured that the oil volume in the pump reaches the standard line. And ensure that the oil quality is clear. If the oil is found to be dirty and saponified, it should be replaced; the new oil should be the special oil for vacuum pump.

(2) The filter screen should be cleaned frequently to ensure smooth air passage.

(3) Depending on the size of the system, a vacuum pump with a suitable pumping speed should be selected to avoid excessive working time and high temperature rise of the pump to damage the rotary vane.