Rotary vane vacuum pump double-stage of structure and working principle
This paper will describe the next two single-stage pump connected in series, forming a double-stage rotary vane vacuum pump structure and working principle.
Mainly due to:
(1) there is harmful space in the structure of single-stage rotary vacuum pump, and the gas in the space cannot be excluded. When the rotor rotates around the vent, this part of the gas is compressed again, through the gap between the rotor and the pump chamber and back to the suction space, so there is always some gas exhaust.
(2) there is a pressure difference between the suction space and the exhaust space of the pump chamber when the single-stage rotary vacuum pump works. When the gas in the exhaust space is compressed very small, its pressure is very high, through all possible ways to break into the suction space to make the pump vacuum drop.
(3) the pump oil will dissolve into a large amount of gas and steam during the circulating flow process in the pump body. In the suction side, because the pressure is lower, dissolved gas will run out, so that the vacuum of the pump is not easy to improve.
In order to improve the ultimate vacuum of the pump, in addition to improving the pump body, rotor, rotor plate processing accuracy, as far as possible to reduce the assembly gap and harmful space, the most effective way is to connect two single-stage pumps in series, forming a double-stage rotary vane vacuum pump.
The pump consists of two workrooms. Ante-stage pump is a low vacuum stage (also known as the first stage, low level), the ante-stage pump is a high vacuum stage (also known as the second stage, advanced), the gas pumped by the ante-stage into the ante-stage, by the exhaust valve discharged from the pump. The front and back stages are slightly different: the back stage of the pump chamber (cylinder) is larger than the front stage, the front stage and unipolar pump, at any time there is oil into the pump chamber, the back stage only at the beginning of the work of a small amount of oil, after a period of time, there is no oil into the pump chamber. When the rear stage works, part of the gas is directly discharged to the atmosphere from the rear valve, and part of the gas is discharged to the atmosphere through the front pump. After working for a period of time, the gas in the rear stage pump after compression, the pressure can not reach more than one atmosphere, push back the valve, these gases are completely the front stage out. With a long pumping time, the pressure at the inlet of the rear stage pump decreases greatly, the pressure at the outlet of the pump is also small, and the pressure difference between the inlet and outlet is small. The amount returned by compressed gas decreases correspondingly. Meanwhile, the oil molecules that are easy to evaporate in the rear stage pump are continuously removed by the front stage pump, so the partial pressure of the oil vapor decreases. This can improve the ultimate vacuum of the pump. And oil pollution is less than single-stage pump.
The mounting positions of the I – and fifth-chamber blades are perpendicular to each other. Therefore, make sure that the first stage of exhaust is the second stage of the exhaust, so that they can work in sync.
When the pump works for A period of time, when the gas pressure in the II chamber is low, the pressure cannot reach more than one atmosphere despite the compression in the II chamber, and the auxiliary exhaust valve cannot be opened, then all the inhaled gas enters the front class A chamber, after the continuous compression in the I chamber, it is discharged by the exhaust valve.
After the pump works for a period of time, since the pressure in the high vacuum stage is greatly reduced, the outlet pressure is also very small, so the pressure difference between the inlet and outlet of chamber II is small, and the amount of compressed gas returned is correspondingly reduced. At the same time, the oil molecules easy to evaporate in the rear stage pump are continuously removed by the front stage I chamber, and the partial pressure of oil vapor is reduced, so the oil pollution of the two-stage pump is smaller than that of the single stage, and the ultimate vacuum degree will be greatly improved. The ultimate vacuum of the two-stage rotary vane vacuum pump before the country can be 10-2 Pa, some foreign pumps can reach 10-3 Pa.
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