In petroleum and chemical production, certain production processes are often carried out under atmospheric pressure. Any pressure lower than atmospheric pressure is called vacuum, and the degree of vacuum commonly used indicates the degree of lower than atmospheric pressure. The machine used to pump gas from equipment below atmospheric pressure is called a vacuum pump. Vacuum pumps are used in the petroleum industry for vacuum distillation, degreasing of lubricants, furfural recovery, etc. In the chemical industry, vacuum pumps are used for vacuum filtration, evaporation, concentration, drying, and crystallization of solutions. Vacuum pumps can also be used as large centrifugal pumps for drainage irrigation pumps.
Mechanical vacuum pumps can be classified into reciprocating type, rotary type (skateboard type), and water ring type according to their structural types.
Any vacuum pump generally uses the following two main parameters to indicate its working performance
(1) Air extraction rate refers to the volume of gas that the vacuum pump draws from the intake pipe under the residual pressure per unit time, that is, the production capacity of the vacuum pump (or called the worldly V), expressed in m³ or L / s.
(2) Residual pressure or ultimate vacuum refers to the lowest pressure (absolute) that the pump can reach.
A certain vacuum pump is used to suck the gas in a closed container. No matter how long the suction time is, the pressure in the container cannot be reduced to zero (that is, absolute vacuum) indefinitely. This is because when the inlet pressure is lower than a certain value, either because the liquid in the pump vaporizes, or because the air disc leaked from the high-pressure side is the same as the vacuum pump's pumping victory. , The volume coefficient is reduced to zero. Both will make the pump unable to continue to inhale fresh gas. In this case, the pressure in the container will never decrease again. The absolute pressure at this time is called the residual pressure or the ultimate vacuum.