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