The vacuum pumps commonly used in chemical production include reciprocating vacuum pump, water ring vacuum pump and jet pump. The structure of reciprocating vacuum pump and piston compressor are basically the same.
The characteristic of vacuum pump is high pressure ratio. For example, to achieve 95% vacuum, the nominal absolute pressure of suction is 0.005MPa, while the exhaust pressure is 0.1MPa, and the pressure ratio is 20. Due to the large pressure ratio, the volume occupied by the gas in the residual clearance volume after expansion is very large, which greatly reduces the suction volume and the effective utilization rate of the cylinder is very low.
In order to solve the above problems, several grooves are generally opened on the cylinder wall at both ends of the cylinder, which are longer than the thickness of the piston. When the piston runs to the dead center position, it is used to balance the pressure of the cylinders on both sides of the piston. For example, when the piston runs to the left dead center, the exhaust end of the left cylinder, the residual gas with high pressure in the clearance volume, and the suction end in the right cylinder, the pressure is low. Due to the connection of the groove, the gas pressure in the clearance volume of the left cylinder will decrease. In this way, the volume occupied by the expansion of the residual gas is greatly reduced and the suction capacity is increased when the piston is running in return. The same is true of the piston running to the right dead center.
Reciprocating vacuum pump is suitable for pumping gas without solid particles and corrosive. 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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