Vacuum pump is a machine used to pump air from equipment or production system to make equipment or production system work in vacuum. The main working performance parameters of vacuum pump are: pumping rate, limit vacuum degree, shaft power and rotational speed. The pumping rate of vacuum pump refers to the volume of gas that can be pumped out per unit time (m 3/h). Limit vacuum is the highest vacuum that a pump can achieve.
Vacuum pumps commonly used in chemical production include reciprocating vacuum pumps, water ring vacuum pumps and jet pumps. The structure of reciprocating vacuum pump is basically the same as that of piston compressor.
Vacuum pump is characterized by high pressure ratio. For example, to achieve 95% vacuum, the absolute pressure of nominal inspiration is 0.005 MPa, while the exhaust pressure is 0.1 Mpa, with a pressure ratio of 20. Because of the high pressure ratio, the volume occupied by the residual gap volume after expansion is very large, which greatly reduces the suction capacity and the effective utilization rate of the cylinder is very low.
In order to solve the above problems, several grooves are usually opened on the cylinder wall at both ends of the cylinder, which are thicker than the piston. When the piston runs to the stop point, the grooves are used to balance the pressure of the cylinders on both sides of the piston. For example, when the piston runs to the left stop point, the exhaust of the left cylinder ends, the residual pressure in the clearance volume is higher, the suction in the right cylinder ends, and the pressure is lower. Because of the connection of grooves, the gas pressure in the clearance volume of the left cylinder decreases accordingly. In this way, the volume occupied by the expansion of residual gas is greatly reduced and the suction capacity is increased during the piston return operation. The piston runs to the right stop.
Reciprocating vacuum pump is suitable for pumping non-solid particles, non-corrosive gas. This kind of vacuum pump is widely used in chemical industry because of its high pumping rate and high vacuum degree.
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