DRY VACUUM PUMP WITH PURGE GAS SYSTEM AND METHOD OF PURGING

摘要

The present invention provides a positive displacement dry pump comprising: a plurality of vacuum pumping stages comprising a respective plurality of pumping mechanisms driven by one or more drive shafts for pumping fluid in series through the pumping stages from a pump inlet at the high vacuum stage to a pump outlet at the low vacuum stage; a lubrication chamber housing a bearing assembly for supporting the drive shaft for rotational movement, the drive shaft extending from the high vacuum stage to the lubrication chamber through an opening of a head plate of the lubrication chamber; an inter-stage purge port through which gas can enter the pump at an inter-stage location downstream of the high vacuum stage and pass only through the or each vacuum pumping stage downstream of the inter-stage port; a lubrication chamber purge port located in the lubrication chamber through which purge gas can flow from a source of purge gas; wherein the inter-stage port is connected to the lubrication chamber for controlling the pressure of purge gas in the lubrication chamber thereby resisting the passage of pumped gases from the high vacuum chamber to the lubrication chamber through the opening of the head plate during use.