Patent ID: 9334863
Filing Date: 2016-05-10
CPC Classification: F04C

Claim Text:
1. 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 a high vacuum stage to a pump outlet at a 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 enters the pump at an inter-stage location downstream of the high vacuum stage; a lubrication chamber purge port located in the lubrication chamber through which purge gas flows from a source of purge gas into the lubrication chamber; wherein the inter-stage purge port is connected to a second purge port located in the lubrication chamber such that purge gas in the lubrication chamber flows out of the lubrication chamber through the second purge port and a conduit external to the pumping stages to the inter-stage purge port to thereby control a pressure of purge gas in the lubrication chamber thereby resisting a passage of pumped gases from the high vacuum chamber to the lubrication chamber through the opening of the head plate during use.