Patent ID: 8297311

Claim:
An apparatus for establishing and controlling a low pressure mixture of gases in a vacuum enclosure, the apparatus comprising: a primary pump adapted to deliver to atmospheric pressure; a secondary pump of a molecular, turbomolecular, or hybrid type, said secondary pump pumping from the vacuum enclosure to the primary pump, to evacuate gases from the enclosure; an intermediate pipe interconnecting the delivery outlet of the secondary pump and a suction inlet of the primary pump; first control and adjustment means, disposed upstream from the secondary pump, for controlling and adjusting the total gas pressure of the mixture of gases in the vacuum enclosure as a function of a total pressure setpoint; and second control and adjustment means disposed downstream from the secondary pump, including means for acting on the delivery pressure from the secondary pump in the range of pressures in which changes of the delivery pressure lead to significant variations in the pumping speeds of different gases of the mixture in a manner that is selective depending on the nature of the gases and means for acting on the delivery pressure in response to a delivery pressure setpoint to adapt the pumping capacity of the secondary pump to selectively pump different gases at different speeds to favor pumping a selected one of the gases from the vacuum enclosure by the secondary pump, to adjust the proportions and the partial pressures of the gases in the mixture of gases in the vacuum enclosure.