# Rotary vane vacuum pump limit pressure

Rotary vane vacuum pump is a kind of varactor mechanical vacuum pump, which utilizes the rotating motion of the rotor and the vane sliding in the rotor slot to obtain vacuum. When the working fluid is used to lubricate and fill the dead gap of the pump chamber, separating the exhaust valve from the atmosphere, it is commonly known as the oil-sealed rotary vane vacuum pump. Without working fluid, it is dry rotary vane vacuum pump.

In oil-sealed rotary vane vacuum pump, the belt-driven rotary vane vacuum pump is customarily called in China, while the direct-coupled rotary vane vacuum pump is directly connected with the motor or with the coupling. In each pump, there are single and double stages. In single-stage pumps, the limit pressure and usage of pumps are different due to the different structure and parameters.

## Rotary vane vacuum pump limit pressure

Their common characteristics are simple structure, easy use, starting from atmospheric pressure, direct discharge of the atmosphere, small eccentric mass, simple maintenance, the limit pressure of two-stage pump is 6 *10-2~l *10-2 Pa, one single-stage pump can reach about 4 Pa, the other single-stage pump is about 50-200 Pa.

Soon after the rotary vane pump started to work, the lowest pressure was P’g. The pump continues to operate. As the pump temperature rises, the saturated vapor pressure of the pump oil rises and the viscosity decreases. The inlet pressure rises slightly to Pg. Pg is the stable minimum pressure of pump and the ultimate pressure of 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 compressed vacuum gauge, the limit pressure value is about one order of magnitude lower than that measured with a heat conduction vacuum gauge (thermocouple or Pixometer, etc.). This is because the former can only measure the partial pressure of the permanent gas, and the latter measured the total pressure of the compressed gas. In China, the compressibility vacuum gauge is used to measure the limit pressure of the oil seal mechanical pump.

The pump circulation oil also affects the ultimate pressure of the pump. With the increase of oil quantity, the better the sealing effect, the relationship between the limit pressure of the pump and oil quantity will change, and finally the saturated vapor pressure of the oil will reach Po. In fact, there is a lot of air and water in the pump oil. When the pump oil enters the pump chamber, the air and water absorbed in the pump oil are released, and the relationship between the pump limit pressure and the amount of oil develops upwards. The general pump oil should be kept at the designated oil level, so that the circulating oil volume of the pump must be maintained. 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 discharge volume of the pump oil in the high vacuum stage, so as to reduce the limit pressure of the pump.

The limit pressure of rotary vane vacuum pump is related to the working temperature of pump oil. The higher the oil temperature, the higher the saturated vapor pressure of the oil, the higher the ultimate pressure of the pump.

Since W. Gaede invented the rotary vane pump in 1909 and obtained the German patent, and invented the gas ballast pump in 1936, and obtained the patent in 1941, the rotary vane vacuum pump has been widely used and continuously improved. At the end of 1960s, the trend of increasing speed and miniaturization of direct connection appeared in the world. At the beginning of 1970s, direct connection products appeared. By the beginning of 1980s, a series of improved products were introduced. There are many accessories for users to choose, which can protect the pump or the environment. The structure of the pump itself has also been improved and the reliability has been improved.

## Rotary vane vacuum pump application

Rotary vane vacuum pump can be widely used in refrigerators, air conditioners, bulbs, fluorescent lamps, bottle production and electronics, metallurgy, medicine, chemical industry, oil filter, printing machinery, packaging machine and other industries. It can be used as a front-end pump for diffusion pump, Roots pump, molecular pump, etc., to supply electronic instruments, medical instruments and other supporting and experimental research applications. . Because direct pump has no dust pollution caused by belt friction, its volume is small, weight is light, material is saved, function is improved day by day, and it is more widely used.

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