The structure and principle of the reciprocating vacuum pump are basically the same as those of the reciprocating compressor, but the valve used is required to be lighter and easier to open and close. When the achieved vacuum degree is high, for example, to obtain 95% vacuum degree (ie, 0.05 [absolute atmospheric pressure]), the compression ratio is very large (about 20), so that the residual gas in the clearance can be used for the vacuum pump. The impact is greater, so we must try to reduce the impact of clearance from all aspects. It is an effective measure to set a balanced air passage between the left and right ends of the vacuum pump cylinder. At the end of the piston exhaust, allowing the balance air passages to communicate for a short time, the residual gas in the clearance can flow from one side of the piston to the other side, thereby reducing its pressure. The outer wall of the cylinder also needs a cooling device to remove the heat generated by gas compression and mechanical friction.

It can be seen that the vacuum pump and the compressor do not exist in isolation from each other. There are differences and connections between them. The difference is obvious. The connection is that under certain conditions, such as connecting its inlet to the atmosphere, the vacuum pump can be used as a compressor. use, and vice versa.

The reciprocating vacuum pump produced in my country is represented by W (to), and there are five main specifications from W1 to W5. This W-type vacuum pump has been widely used in various industrial sectors, and chemical plants are often used in vacuum distillation, evaporation, crystallization, drying and filtration operations. This kind of pump is a dry vacuum pump, that is, the pumped gas should not contain liquid, or try to remove the liquid contained in it before entering the pump.

The main performance parameters of the vacuum pump are:
(1) Pumping rate, that is, the volume of gas inhaled by the vacuum pump under the residual pressure per unit time, that is, the production capacity of the vacuum pump, expressed in [m3/hour]. For example, the pumping range of the w-type vacuum pump is 60~770 [m3/hour].

(2) Residual pressure or ultimate vacuum, which is the lowest pressure that a vacuum pump can achieve. It is customary to express it in "torr" in addition to % vacuum degree, 1[torr]=1/760 of standard atmospheric pressure. For example, the ultimate vacuum of the w-type vacuum pump can reach 10 [torr, absolute], which is one of the rough vacuum equipment.

The selection of vacuum pump is based on the above two indicators. Of course, the power required by it should also be considered when selecting it, in order to be economical and reasonable.