Roots vacuum pump is a kind of rotary positive displacement vacuum pump. Its structure is evolved from roots blower. In order to adapt to the vacuum melting system with large pumping speed in the pressure range of 10-1000pa, it is used as a mechanical booster pump.
According to the different working pressure range of Roots vacuum pump, it is divided into
1. Low vacuum roots pump: dry single-stage roots pump (10000pa) and wet roots pump (2000Pa) with direct air discharge;
2. Medium vacuum roots pump: mechanical booster pump (1 × 10-1 PA);
3. High vacuum roots pump: multistage dry roots pump (high vacuum multistage roots pump;
The largest domestic consumption is medium vacuum roots vacuum pump (hereinafter referred to as roots vacuum pump).
Compared with other mechanical pumps, roots vacuum pump has the following characteristics:
1. There is a large pumping speed in a wide pressure range;
2. The rotor has good geometric symmetry, so the vibration is small and the operation is stable. There is clearance between rotors and between rotors and shells, no lubrication, small friction loss, which can greatly reduce the driving power, so as to achieve higher speed;
3. The pump cavity does not need to be sealed and lubricated with oil, which can reduce the pollution of oil vapor to the vacuum system;
4. There is no compression and exhaust valve in the pump cavity. Simple and compact structure, insensitive to dust and water vapor in the extracted gas;
5. The compression ratio is low and the effect of hydrogen extraction is poor;
6. The surface of rotor is curve cylinder with complex shape, so it is difficult to process and check.
Roots vacuum pump in vacuum engineering
1. In the middle vacuum range, it is used as a mechanical booster pump, which is usually connected in series with the front pump (vane pump, slide valve pump, water ring pump, etc.) to form a vacuum unit;
2. High vacuum can be obtained by two-stage or multi-stage Roots pump unit;
3. For dry clean oil-free pumping system, multi-purpose air-cooled Roots pump unit is used;
4. For water vapor extraction system, wet roots pump is often used;