Due to contain a certain amount of water vapor in the atmosphere, so when the vacuum pump working the suction air also contain some non-condensable gas and the mixture of permanent gas.This gas mixture is compressed within the pump exhaust process, if partial pressure of non-condensable gas pass than the pump under the temperature of saturated vapor pressure, then they will condense and mixed with pump oil, with oil circulation.When they returned to the high vacuum evaporation and steam again.Increasing with the pump running, the condensation, the limit of the vacuum pump and pumping speed reduced.Humidity is bigger when pumping the gas, the pump oil pollution is more serious, sealing of pump, lubrication and cooling performance is poor, often that change new oil.
Gas ballast valve is to prevent the steam condensation in order to avoid the effective method to oil pollution.This method is to room temperature dry air hole bullishness of town into the compression chamber of pump and is pumped gas mixture.When the mixed gas compression to the exhaust pressure, due to the aeration effect makes the steam partial pressure can maintain the pump temperature under the condition of saturated vapor pressure, and steam will not together with the other gas condensation is to the pump.Gas is pumped, the more content of steam in mixed with dry gas amount is required.
Adopts the method of gas ballast, although achieved the purpose of exclusion of steam, but due to the aeration increasing the potential breakthrough to leak into the atmosphere to the suction side, so to have influence on the pumping speed and limiting vacuum pump.Pump in the aeration process, and its ultimate vacuum than not aeration falls 1 ~ 2 orders of magnitude.Generally when use, first to use the gas ballast valve aeration can non-condensable gas.Wait until after the steam ejector basic, can close the gas ballast valve and continue to smoke gas, after a certain period of time, can be reached when not in aeration limit vacuum pump.
Due to the method of gas ballast is mainly to prevent the pump in the process of compressed vapor condensation, so for those who are from the gas phase state can dissolve in the pump oil vapor ejector effect is poor.
Device with a gas ballast mechanical vacuum pump which include oil sealed rotary vane vacuum pump, and the purification of oil pump function: after the oil pump is a small amount of condensation water pollution, as long as the pump inlet to block, and then open the gas ballast valve, suction operation after a certain time, oil pump can restore the original performance.