Gas recirculation flow control method and apparatus for use in vacuum system

摘要

A gas recirculation flow control method and apparatus for use in an evacuation system having a vacuum chamber into which a gas is introduced, a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber. The recirculation flow rate Q2 of the gas returning to the vacuum chamber through the gas recirculation line is controlled by adjusting the differential pressure Pd-Pc in the gas recirculation line by varying the effective pumping speed of the second vacuum pump using the following relationship:where: Q2 denotes the recirculation flow rate of the gas returning to the vacuum chamber through the gas recirculation line; Pc denotes the pressure in the vacuum chamber; Pd denotes the pressure in the upstream side of the gas recirculation line; and C denotes the conductance of the gas recirculation line.