Various vapors or mixtures of vapors and gases are often discharged in vacuum applications, mainly steam. Ordinary rotary vane vacuum pumps can’t rule out steam, steam into rotary vane pump after the studio will be compressed, the pressure increase gradually to the saturated vapor pressure (saturated vapour pressure of water vapor in 20 ℃ 2.3 x103Pa, at 60 ℃ for 2 x104pa), exhaust valve is not opened, excess vapor began to condense into liquid, and vapor line not to go out.
The coagulant and pump oil are mixed to form a suspension, which makes the characteristics of pump oil significantly worse. At the same time, the condensate with high saturated vapor pressure circulates with the pump oil to the inlet valve and evaporates into the pumped space again, which greatly aggravates the extreme vacuum. Especially when water vapor condenses into water, it will cause chemical reactions in the pump.
First, interaction to generate the softened water with cast iron iron, iron oxide with water to generate hydrogen ferric oxide, ferric hydroxide and produced from organic acids play a role in oil saponification soap (iron), and saponification material is also accelerating oxidation catalyst.
Due to pump oil constantly absorb the moisture in the compression process, the effect of continuous happen, finally, has thickened oil pump serious fat changes, make the rotor rotation is difficult, pump, high temperature causes the pump seal, lubrication and cooling performance, greatly reduces the working life of the pump.
If the steam is corrosive, the pump body will soon be seriously corroded. In order to avoid the influence of condensation water on the pump performance, the most simple and effective way is by air to prevent vapor condensation in the pump, namely in the part of a compression space by one adjustable mixed gas mixing valve (i.e., gas ballast valve).
When the pump works, a certain amount of gas is added into the valve compression space to mix it with the steam. Before the steam condenses during the compression, the pressure of the mixture exceeds 0.1mpa, so the exhaust valve can be pushed out of the pump and the steam can be eliminated. The amount of gas star depends on the amount of vapor.
Although steam can be removed through a pneumatic valve, it can reduce the limit vacuum of the pump by an order of magnitude. Therefore, in practical use, when steam is removed, the valve should be closed in time. Vacuum electronic device exhaust, generally do not need to use gas valve.
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