Impact of backing pumps on the vacuum system
In many applications, the maximum end pressure of a vacuum system is mainly traced back to the parameters of the high vacuum pump in use. But the characteristics of vacuum systems are not only determined by the high vacuum pump but to a remarkable degree also by the backing pump and the alignment inside the whole pumping station.
A vacuum pump or a pumping station supports the gas flow which is emitted by the vacuum system. In case of a vacuum process to which process gases are added, the gas throughput is determined by this process gas flow. If, in contrast, the vacuum system is supposed to reach a low end pressure without added gases, the gas throughput is mainly determined by the gas emitted from the inner surfaces of the vacuum system.
Test setup for qualifying a pump combination of ACP backing pump and HiPace turbopump
Selecting a suitable backing pump
If a backing pump is selected for a pumping station, the pump must generate a pressure which is smaller than the maximum fore vacuum pressure of the high vacuum pump in use. This maximum fore vacuum pressure can be found in the specifications of each and every turbopump and is named “forevacuum max.”, “max. fore vacuum” or “fore pressure”. Depending on their construction type and manufacturer, modern turbopumps with Holweck stage can be operated with a high fore vacuum pressure of more than 20 mbar.
So the possibilities of selecting the pumps from the standard backing pumps offered are almost not limited at all. This does not restrict the selection of standard backing pumps. Many backing pumps such as oil-lubricated rotary vane pumps, compact diaphragm pumps or high-performance dry pumps can generate this fore vacuum pressure against atmosphere.