Piston pumps are used for most large scale vacuum applications. These pumps have a sliding sleeve through which the gas enters, then drawn into a cylindrical chamber and exhausted by a 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 1 x 10-4 Torr. Rotary piston pumps can be prepared for corrosive and oxygen service.