초록 ▼

A pump includes a plurality of pumping stages comprising a respective plurality of pumping mechanisms driven by one or more drive shafts for pumping fluid 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 beari

A pump includes a plurality of pumping stages comprising a respective plurality of pumping mechanisms driven by one or more drive shafts for pumping fluid 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 can enter the pump at an inter-stage location downstream of the high vacuum; 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.

대표청구항 ▼

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 va

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. 2. The pump as claimed in claim 1, wherein the location of the inter-stage purge port is selected so that in use the pressure of purge gas in the lubrication chamber is generally higher than the pressure of pumped gas in the high vacuum chamber providing a positive pressure differential between the lubrication chamber and the high vacuum stage. 3. The pump as claimed in claim 1, wherein the pressure at the inter-stage purge port is responsive to pressure of pumped gas in the high vacuum stage so that a change in pressure in the high vacuum stage causes a corresponding change in pressure of purge gas in the lubrication chamber. 4. The pump as claimed in claim 3, wherein an increase of pressure of pumped gas in the high vacuum stage causes an increase in pressure of purge gas in the lubrication chamber so that during an increase of flow of pumped gas into the high vacuum chamber the pressure of purge gas in the lubrication chamber is increased to resist passage of pumped gas from the high vacuum stage to the lubrication chamber through the opening in the head plate. 5. The pump as claimed in claim 1, wherein the lubrication chamber purge port is located in the head plate so that purge gas flows into a shaft seal in the opening of the head plate. 6. The pump as claimed in claim 1, wherein the second purge port is connected to the inter-stage purge port by a conduit and wherein the conduit comprises a restriction. 7. A method of purging a positive displacement dry pump, the 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 high vacuum stage to a low vacuum stage; anda 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;wherein the method comprises: conveying purge gas from a source of purge gas to the lubrication chamber;controlling the pressure in the lubrication chamber by connecting the lubrication chamber to an inter-stage port located downstream of the high vacuum stage which in use is at a higher pressure than the high vacuum stage so that the pressure of purge gas in the lubrication chamber is higher than the pressure of pumped gas in the high vacuum chamber thereby providing a positive pressure differential between the lubrication chamber and the high vacuum stage wherein a change in pressure in the inter-stage port causes a corresponding change in pressure of the purge gas conveyed to the lubrication chamber. 8. The method as claimed in claim 7, comprising controlling the pressure of purge gas in the lubrication chamber so that it is higher than pressure of pumped gas in the high vacuum chamber irrespective of pressure changes in the high vacuum chamber. 9. The method as claimed in claim 8, wherein the pressure of pumped gas at the inter-stage port is responsive to pressure of pumped gas in the high vacuum stage and pressure of purge gas in the lubrication stage is responsive to pressure of pumped gas at the inter-stage port so that changes in pressure of the high vacuum stage cause changes in pressure in the lubrication chamber. 10. 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 purge 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 and connected to a source of purge gas such that purge gas from the source of purge gas flows through the lubrication chamber purge port;wherein the inter-stage port is connected to the lubrication chamber for controlling the pressure of purge gas in the lubrication chamber such that the pressure of purge gas in the lubrication chamber is higher than the pressure of pumped gas in the high vacuum chamber thereby providing a positive pressure differential between the lubrication chamber and the high vacuum stage wherein a change in pressure in the inter-stage purge port causes a corresponding change in pressure of the purge gas conveyed to the lubrication chamber. 11. The pump as claimed in claim 10, wherein the pressure at the inter-stage purge port is responsive to pressure of pumped gas in the high vacuum stage so that a change in pressure in the high vacuum stage causes a corresponding change in pressure of purge gas in the lubrication chamber. 12. The pump as claimed in claim 10, wherein the lubrication chamber purge port is located in the head plate so that purge gas flows into a shaft seal in the opening of the head plate. 13. The pump as claimed in claim 10, wherein the lubrication chamber purge port is connected to the inter-stage purge port by one or more conduits having a restriction so that the pressure at which purge gas flows into the lubrication chamber is controlled by the pressure at the inter-stage purge port. 14. The pump as claimed in claim 13, wherein the conduit comprises a one-way valve for resisting the passage of pumped gas from the inter-stage port to the lubrication chamber. 15. The pump as claimed in claim 10, wherein the lubrication chamber comprises a second purge port which is connected by a conduit to the inter-stage purge port so that purge gas flows from the lubrication chamber to the inter-stage purge port.