Low vacuum devices such as vacuum conveying, vacuum impregnation, vacuum filtration, vacuum monotony, vacuum degassing (disposal of molten steel), etc. require a low vacuum pump extraction unit with high working pressure and large exhaust volume, and the main pump of this type of low vacuum extraction unit Commonly used reciprocating vacuum pumps, oil-sealed vacuum pumps, water vapor emission pumps, water ring pumps, Roots pumps, etc. The low-vacuum extraction unit used also needs to be equipped with necessary dust collectors, monotonous tanks and other components according to the cleanliness, humidity or other special requirements of the extracted gas.

During the compression process, the water vapor will condense into water droplets and mix with the pump to form a suspension, which not only reduces the vacuum degree, but also causes the pump cavity and rotor to rust, destroys the sealing surface, and reduces the ultimate vacuum degree of the pump. For this reason, it is important to prevent contamination of the mechanical pump with water vapor. Preventive measures include:

(1) Select an oil-sealed mechanical pump with a gas ballast device;

(2) Oil separators, centrifugal separators or oil-water separators, stop the disposal of mechanical pump oil mixed with water, and then flow the treated oil into the pump for use;

(3) Use a monotonic agent with strong water absorption;

(4) The use of liquid nitrogen cold trap can not only effectively absorb water vapor, but also prevent the mechanical pump oil from flowing back into the high vacuum chamber.

Pollution and Prevention of Oil Diffusion Pump Vacuum System
The oil diffusion pump vacuum system is the most commonly used vacuum system, and its vacuum degree ranges from 1.3×10-3 to 1.3×10-5 Pa. Various types of vacuum devices composed of oil diffusion pump vacuum system, after long-term use, the common disadvantage is that the vacuum degree cannot be pumped up, or the vacuum degree cannot be pumped to the original ultimate vacuum level. It is related to the oil vapor pollution of the inner wall of the vacuum chamber and the pollution of various pollutants in the vacuum process. The methods of prevention are:

(1) Clean the vacuum chamber regularly;
(2) Regularly clean the oil-sealed mechanical vacuum pump and oil-metal diffusion pump.