What is the role of gas ballast in oil-sealed vacuum pumps?
I believe that many people will see Gas ballast in the specifications or illustrations of some oil-sealed vacuum pumps. For example, there may be two kinds of vacuum performance of the rotary vane vacuum pump. One is the value of the open gas town. And the other is not the value of the town. What role does this gas town play?
When it comes to gas towns, it is necessary to talk about permanent gases and condensable gases. Some of the gases in our lives and work, such as oxygen, nitrogen, hydrogen, methane and helium, cannot be compressed and liquefied at room temperature. We call them permanent gases. In contrast, the most common ones, such as water vapor, can be liquefied by compression, which we call condensable gases.
Regardless of whether it is an oil-sealed vacuum pump or a dry vacuum pump, in the process of removing the condensable gas, once the pressure of the pumped gas exceeds the saturated vapor pressure of the gas at that time, condensation of the condensable gas occurs. The oil-sealed vacuum pump has the presence of lubricating oil in the pump chamber. When the condensable gas condenses, the condensed liquefied gas will cause the pump oil to be contaminated on the one hand, and the pump oil will be emulsified over time to lose the lubrication protection effect. On the other hand, the condensed gas will re-evaporate when it returns to the low pressure end, causing the vacuum pump's vacuum performance and pumping efficiency to drop. The gas town is set up to solve this phenomenon of the oil-sealed vacuum pump.
Its working principle is also relatively simple, that is, when the partial pressure of the condensable gas exceeds the saturated vapor pressure of the gas and the overall pressure in the pump chamber does not reach the exhaust pressure, the gas is continuously filled into the drying permanent. The gas causes the overall pressure in the pump chamber to reach the exhaust pressure in advance, and discharges, thereby preventing condensation of the condensable gas. During the discharge process, the filled permanent gas is also discharged together with the gas in the original pump chamber.
The above is the role played by gas town in oil-sealed vacuum pumps. However, even in the presence of gas towns, oil-sealed vacuum pumps are only suitable for removing a certain amount of condensable gas. Once a large number of them appear, the efficiency cannot be guaranteed. The dry vacuum pump may also have gas condensation phenomenon, but because there is no pump oil in the dry vacuum pump, the extraction performance of the condensable gas is better than various oil-sealed vacuum pumps.
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