Roots blowers

Leybold RUVAC roots blowers are used in combination with backing pumps to achieve lower pressures, higher pumping speeds and used when larger capacities are required. Classic roots blowers are equipped with a pressure switch for protection against thermal overload, while roots blowers operated by frequency converters or with internal bypass lines can run continuously.
In combination with backing pumps, which compress against the atmosphere, these pumps can improve the attainable ultimate pressure of a pump system by a factor of 10. With two Roots vacuum pump stages and a corresponding backing pump it is possible to attain pressures in the range down to 10-5 mbar (0.75 X 10-5 Torr).
Roots blower are positive displacement pumps without internal compression. This means that they are not able to compress to atmosphere directly and need a corresponding backing pump. When selecting a combination of backing pump and roots pump, the ratio of the pumping speeds of the two pumps is decisive. This is referred to as gradation. Typical gradations are between 1:2 and 1:8. This means that roots blower typically have a pumping speed 2 to 8 times higher than that of the attached backing pump. The gradation determines the pressure difference between the inlet and outlet of the roots pump at the respective operating point. In principle, the required motor power is directly dependent on and proportional to this pressure difference. To avoid overloading the motor and overheating the pump, the pressure difference across the roots pump must not exceed a certain value.