What Is The Ultimate Pressure Of The Vacuum Pump?
Jun 26, 2019| Shortly after the vacuum pump started working, the lowest pressure P'g appeared. The vacuum pump continues to operate. As the vacuum pump temperature rises, the saturated vapor pressure of the vacuum pump oil rises and the viscosity decreases, and the inlet pressure slightly rises to Pg. Pg is the stable minimum pressure obtained by the vacuum pump and also the ultimate pressure of the vacuum pump.
The ultimate pressure of the rotary vane vacuum pump is related to the type of vacuum gauge used in the measurement. When measured with a compression gauge, the ultimate pressure value is about an order of magnitude lower than that measured with a thermally conductive vacuum gauge (thermocouple or picometer). This is because the former can only measure the partial pressure of the permanent gas, and the latter measures the total pressure of the pressurized gas. China's current regulations use a compression vacuum gauge to measure the ultimate pressure of the oil seal mechanical vacuum pump.
The amount of circulating oil in the vacuum pump also affects the ultimate pressure of the vacuum pump. As the amount of oil increases, the sealing effect is better, the relationship between the ultimate pressure of the vacuum pump and the amount of oil changes, and finally the saturated vapor pressure Po of the oil is reached. In fact, the vacuum pump oil contains a large amount of air and moisture. After the vacuum pump oil enters the vacuum pump chamber, the air and moisture absorbed in the vacuum pump oil are released again, and the relationship between the ultimate pressure of the vacuum pump and the amount of oil is developed upward. Generally, the vacuum pump oil should be kept at the specified oil level to keep the circulating oil volume of the vacuum pump constant. For the two-stage vacuum pump, the vacuum pump oil can be degassed through the low vacuum stage before entering the high vacuum stage, which can reduce the venting amount of the vacuum pump oil in the high vacuum stage to reduce the ultimate pressure of the vacuum pump.
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