US Patent 7189066 Light gas vacuum pumping system

A vacuum pumping system includes a primary vacuum pump having an inlet for coupling to a system, and a secondary vacuum pump having an inlet coupled to the exhaust of the primary vacuum pump. The primary vacuum pump is an oil-free, positive displacement vacuum pump having multiple clearance seals between the inlet and the exhaust. The primary vacuum pump may be a scroll vacuum pump, and the secondary vacuum pump may be an oil-free diaphragm pump. The system may include a valve coupled to the exhaust of the primary vacuum pump and configured to couple the exhaust of the primary vacuum pump to an interpump exhaust in response to a selected condition, such as the pressure level at the exhaust of the primary vacuum pump.