Apparatus for supplying a purge gas to a multistage vacuum pump 7 such that the apparatus comprises a gas inlet 9 in fluid communication with a plurality of gas outlets 11 for supplying gas to respective ports of the multistage pump, where the gas outlets have control orifices for supplying gas to the respective ports at proportionally fixed gas flow rates and the apparatus further comprising a control module 17 for controlling the gas flow to the gas inlet in response to a control signal. Preferably the orifices in the outlets are defined by fixed or variable restrictors that have a fixed size ratio relative to each other. The control module may be operable to adjust the pressure of gas supplied to the gas inlet and comprise a variable restrictor to vary the gas flow rate through the gas inlet. A pump system and method for supplying a purge gas is also claimed.
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