Piston pumps are used for most large level vacuum applications. These pumps have got a sliding sleeve by which the gas enters, then drawn into a cylindrical chamber and exhausted by a Rotary Piston Vacuum Pump rocking piston plunger. These pumps are very hardy and have pumping speeds that range from 15 cfm to 2,000 cfm and the pumps can reach a pressure of just one 1 x 10-4 Torr. Rotary piston pumps could be ready for corrosive and oxygen services.
Rotary Piston Vacuum Pump