Rotary vane vacuum pump gas ballast principle：
Open a small hole in the compression chamber of the oil-sealed mechanical vacuum pump and install a regulating valve. When the valve is opened and the amount of air intake is adjusted, when the rotor turns to a certain position, air penetrates into the compression chamber through this hole to reduce the compression ratio. As a result, most of the steam is not easily condensed and the mixed gas is discharged out of the pump. The valve that plays this role is called a gas ballast valve.
Reason: Since the pumping process of the vacuum pump is a compression process, if a condensable gas such as water vapor reaches its saturated steam pressure before being discharged from the pump cavity, it will condense in the oil and emulsify the pump oil. Lubrication and sealing performance deteriorates, and the condensate will return to the gaseous state in the suction chamber, thereby reducing the vacuum.
Principle: The pressure of the exhaust chamber is composed of two parts: air partial pressure and steam partial pressure. Exhaust occurs only when the sum of the two is sufficient to overcome the atmospheric pressure and elastic force of the exhaust valve. The role of the gas ballast valve is to fill the exhaust chamber of the pump with a certain amount of air before the exhaust occurs to reduce the partial pressure of steam in the exhaust pressure. When it is lower than the saturated vapor pressure at the pump temperature, that is It can be discharged out of the pump as it is filled with gas, avoiding condensation in the pump oil. In addition, when the closed pump door is running, the condensate of condensable gas that has been mixed into the oil will be dissolved in the oil, and the substance in the oil will overflow from the oil in the pump cavity. If the gas ballast valve is opened at this time , It can also be pumped out-a certain amount of condensable substances, so as to play a certain role in purification and prolong the service life of the pump oil. Vacuum pump oil is more expensive and the supply is limited, so the rational use of gas ballast has great economic significance.
Gas ballast valve advantages and disadvantages:
1.Can meet the requirements of pumping humid air without causing water vapor to pollute the oil.
2.Purify the pump oil of the vacuum pump.
3.Restore the ultimate vacuum of the vacuum pump.
Atmosphere will leak into the suction end of the pump, affect the pumping speed and ultimate vacuum, and reduce the ultimate vacuum of the pump. But it only has an effect when the gas ballast valve is working.
Edited by Bella Yang / Shanghai EVP Vacuum Technology Co., Ltd
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