Some of the chemical production process, often need to be at less than atmospheric pressure. Vacuum is an absolute pressure lower than atmospheric machinery and equipment. Many structural type vacuum pump, hereby the chemical commonly used in several types of vacuum pumps are described below.
1. reciprocating pump
Reciprocating pump and reciprocating compressor works basically the same structural ,the difference is not large, but the use of the valve must be more Lightweight, easy to open and close. When required to achieve a high degree of vacuum, the compression ratio is large, the impact over a large gap will residual gas, so the vacuum system must be small clearance. In order to reduce the influence of SHE gap between the left and right ends of the cylinder pump set balance airway. When the piston end of the exhaust, so that the balance of airway communicating a very short time, so that the gas flows over the residual gap from one side of the piston, thereby reducing its pressure.
2, the water ring vacuum pump
There is a circular shell eccentrically mounted impeller, pump contains a certain amount of water. When the rotor rotates, the centrifugal force, the water thrown to the shell wall of the water ring is formed. The water ring acts as a seal, the closed gap between the blades into a plurality of chambers of different sizes. The rotor rotates to the right half portion, a small volume of the sealed chamber gradually expanded, the gas intake port from the right; the rotor rotates to the left part, gradually narrowing the small chamber, the gas will be discharged from the exhaust port to the left.
Its cycle of water ring vacuum formed by water temperature limit, generally up to about 83.4x103Pa. The pump can also be used as a blower, the pressure generated by the (gauge pressure) is not more than 98.07x103Pa.
Water ring vacuum system structure is simple, compact, easy to manufacture, easy maintenance, and because there is no mechanical friction rotating parts, so long life.
liquid ring vacuum pump is suitable for conveying corrosive or explosive gases. The disadvantage is low efficiency, typically 30 to 50%.
3, the water jet pump
If the jet pump working fluid is water, the water jet pump is called; if it is water vapor, it is called vapor jet pump.
Single-stage steam jet pump pressure up to 0.01MPa, to achieve a higher degree of vacuum, can be multi-injection system.
Advantages jet pump working pressure range is wide, pumping capacity, simple structure. The disadvantage is inefficient.