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.
Classic roots blowers, WA & WS series, are equipped with simple flange-mounted or integrated motors that are directly supplied with mains voltage and run at a constant speed. Since the motor load increases with rising suction pressure, these roots pumps may be cut in below a certain pressure only. Therefore, this type is only suitable for very long pumping cycles or for stationary operation at low pressure. For fast, cyclical pumping, switching the roots stage on and off constantly is not practicable. In order to protect the roots pump reliably a pressure gauge monitoring the pump’s cut-in point is always required. There are several principles available to seal the drive shaft under vacuum against atmospheric pressure.
With the three different series WA, WS and WH, Leybold offers a range of solutions for different industrial applications.
The RUVAC WA / WAU roots blowers are equipped with a flange-mounted motor. The drive shaft is fed through shaft seals to the outside. This allows simple and cost-effective standard motors to be flange-mounted.
The RUVAC WS / WSU roots blowers are equipped with a canned motor. The motor rotor and stator are separated by a thin-walled cartridge for an absolute hermetically sealed pump important for pumping aggressive or toxic media. Motors of the WS series are available both water-cooled and air-cooled. As there are no shaft seal rings, the WS pump is easier to maintain.
The RUVAC WH / WHU roots blowers are equipped with a hermetically sealed motor. WH pumps are airtight and suitable for pumping toxic gases, which must not be discharged into the environment. Unlike canned motor pumps, WH pumps feature a plastic encapsulation of the entire motor stator, separating it from the motor rotor that runs in a vacuum. By removing the metallic can and applying smaller gaps, this technology achieves higher efficiencies. The WH series features integrated water cooling and is particularly energy efficient.
Leybold roots blowers are available with integrated frequency converters and can also be operated with external converters.
An elegant and energy efficient solution to protect roots blowers from overload is the use of frequency converters. These converters adapt the pump's motor speed to the load and enable safe operation in all working ranges. At high pressure, the pump rotates more slowly and accelerates to lower pressures until the maximum speed is reached. Moreover, all Leybold roots blowers using frequency controllers can also be operated at higher speeds than the corresponding Direct-Online version. This allows to increase the achievable pumping speed in the lower pressure region significantly.
Roots blowers with frequency converter can be easily monitored, connected to the network and are industry 4.0 ready.