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Limit pressure of rotary vane vacuum pump  

 
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Limit pressure of rotary vane vacuum pump

Soon after the rotary vane vacuum pump began to work, the minimum pressure P'g appeared. The pump continued to run, because of the increase of pump temperature, the saturated vapor pressure of pump oil increased, the viscosity decreased, and the inlet pressure slightly increased to PG. PG is the minimum stable pressure obtained by the pump and also the ultimate pressure of the pump.

The limit pressure of rotary vane vacuum pump is related to the type of vacuum gauge used in measurement. The results show that the limit pressure is about one order of magnitude lower than that measured by a heat conduction vacuum gauge (thermocouple or piezometer, etc.). This is because the former can only measure the partial pressure of the permanent gas, and the latter can measure the total pressure of the compressed gas. The current regulation of our country is to measure the limit pressure of mechanical pump with oil seal by using compression vacuum gauge.

The amount of circulating oil also affects the limit pressure of the pump. With the increase of oil quantity, the sealing effect is better. The relationship between the limit pressure and oil quantity of rotary vane vacuum pump changes, and the saturated vapor pressure Po of oil is finally reached. In fact, the pump oil contains a lot of air and water. After the pump oil enters the pump cavity, the air and water absorbed in the pump oil are released again. The relationship between the pump limit pressure and the oil quantity develops upward. Generally, the pump oil should be kept at the specified oil level to keep the circulating oil volume of the pump constant. For the two-stage pump, the pump oil can enter the high vacuum stage only after degassing in the low vacuum stage, which can reduce the amount of bleeding of the pump oil in the high vacuum stage and reduce the limit pressure of the pump.

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Posted : November 16, 2020 4:03 pm
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