The use of gas ballast in rotary vane vacuum pumps

The ballast valve can accelerate the extraction of steam without polluting the oil. If the rotary vacuum pump only pumping permanent gas, the gas does not liquefy due to the increase in pressure, so there is no deterioration of the pump oil. However, if the pump is used to vacuum dry or pumping humid air, the gas will have not only permanent gas but also Water vapor, if this portion of water vapor is pumped out with a pump without a gas ballast, the vapor will be liquefied and dissolved in the oil, the vacuum properties of the oil will be degraded, thus reducing the pumping speed and vacuum degree of the pump. The further description of the steam compression process is as follows:

Vapor pumped by the pump will be compressed in the compression chamber until the exhaust valve opens.then vapor compression, to the end of compression have been all condensed into water, mixed with oil. in order to meet the requirement of pumping moist air without contaminating the oil with vapor, the rotary vane vacuum pump is equipped with a gas ballast device. The principle is to put a certain amount of air in the compression process to increase the pressure of the mixed gas, the gas mixture The pressure is the sum of the partial pressure of air and the partial pressure of steam. When the partial pressure of steam has not yet reached the saturated steam pressure at the pump temperature, the pressure of the mixed gas exceeds the pressure of the exhaust valve and opens the exhaust valve so that the steam is too late. Liquefaction in the pump chamber is excluded from the pump.

Gas ballast valve also can be used to restore the ultimate pressure of the vacuum pump. Sometimes the normal air is drawn. There is less gas containing condensable gas. Generally, the gas ballast valve is closed, but when the time is long, the oil is gradually in the air. The small amount of condensable gas contained is contaminated. For a pump without a gas ballast, only replacing the new oil or heating the pump oil will allow the liquefied steam to evaporate to restore the original limiting pressure of the pump. For the pump, the rotary vacuum pump’s ultimate pressure can be restored by turning on for 1 to 2 hours.

In the process of pumping gas, open the ballast valve, although the purpose of eliminating the steam is achieved, but because the atmosphere will leak to the suction side of the pump, affecting the pumping speed and the ultimate vacuum, so that the ultimate vacuum of the pump is reduced. Therefore, when using a vacuum pump with a gas ballast, first open the ballast valve to remove the condensable gas, wait until the basic pumping is done, and then close the ballast valve. To reach the original vacuum of the pump, it takes some time to pump.

The rotary vacuum pump installed with the gas ballast device 2 not only can extract the condensable gas, but also can purify the pump oil. If the pump oil is contaminated by a small amount of condensate, just plug the pump air inlet and open the gas ballast valve. After pumping for a certain period of time, the pump oil can restore its original performance.


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