Piston pumps are used for some large level vacuum applications. These pumps possess a sliding sleeve by which the gas enters, then drawn 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 Rotary Piston Vacuum Pump pressure of just one 1 x 10-4 Torr. Rotary piston pumps can be ready for corrosive and oxygen support.