Roots vacuum pump is generally in the form of vacuum unit, because ordinary roots pump can not start and directly exhaust the atmosphere under normal pressure and high pressure, so it needs to be equipped with front pump. But not all roots vacuum pumps need to start the front stage pump, such as air-cooled Roots vacuum pump, wet root vacuum pump and multi-stage Roots vacuum pump.
The ordinary roots vacuum pump can only be started at 6000pa or even lower pressure, and has a stable large pumping speed between 1333pa and 1pA. Because roots vacuum pump has no internal compression characteristic, it is realized by external compression in the form of gas emission. Too high pressure and high-pressure operation will make the vacuum pump load too high, so that the rotor can not be too large in the compression process of heat dissipation, will produce too large expansion, resulting in the gap between the rotor and the pump cavity disappeared, that is, stuck.
In order to solve this problem, the cooling gas is used to directly cool the rotor to reduce the temperature difference between the rotor temperature and the pump cavity, so as to avoid excessive expansion of the rotor to achieve high pressure and high compression ratio operation. Therefore, it can be used alone under atmospheric pressure, and it can also be used to increase the vacuum degree of multiple single elements in series.
It can be seen from the figure that there is not much difference in the structure and principle between air-cooled Roots vacuum pump and ordinary roots vacuum pump. A connected cooler is mainly arranged at the pump outlet, and cooling gas is introduced at both sides of the pump to cool the rotor. With this structure, roots vacuum pump can be started directly under atmospheric pressure and work independently. Independent direct air, air-cooled Roots vacuum pump pressure limiting pump is about 1 × 104pa, the lower limit pressure can be obtained in series. The working pressure can reach 88kpa.
Through the above changes, the air-cooled Roots vacuum pump can not only work directly under atmospheric pressure, but also has a stable pumping speed curve in the high-pressure section, which can greatly shorten the pumping time in the pumping stage. Compared with other direct gas sealed pumps, the air-cooled Roots vacuum pump has good energy saving characteristics under high pressure.