What is the role of a forepump in a high-vacuum system?

In vacuum technology, a forepump—also known as a backing pump—serves as an essential auxiliary component that provides the first stage of exhaustion for a high-vacuum system.1

Because many high-vacuum pumps cannot operate efficiently at atmospheric pressure, they must be backed in series by a forepump to function within their intended pressure ranges. The forepump reduces the pressure to a level where the primary high-vacuum pump can take over, and it continues to operate to remove the gas discharged by that primary pump.21

The most frequently utilized type of forepump is the oil-sealed rotary pump. In complex industrial applications, such as secondary steelmaking, vacuum pumping systems often integrate multiple mechanical pumps to lower the pressure initially, followed by additional stages—such as steam ejectors—to reach the extremely low pressures required for processes like vacuum decarburization.23