housing differential vacuum pumping ports located on the outer edge 204 of the fixed sealing housing 200 these housing vacuum channels 203 may disposed throughout the fixed seal housing 200 in any pattern this housing differential vacuum pumping port may be in communication with a pump such as a vacuum pump not shown the distal ends of the housing vacuum channels 203 terminate at the upper surface of the floating seal cartridge 220 the housing vacuum channels 203 in combination with the vacuum pump serve to evacuate the pressurized air from the interface 208 so that this pressurized air does not enter the process chamber 100 in other words the layer of pressurized air in the interface 208 between the fixed seal housing 200 and the floating seal cartridge 220 when used with housing vacuum channels 203 and a vacuum pump acts as a seal isolating the external environment from the environment within the process chamber 100 and maintaining the desired pressure differential between these environments fig6 shows one particular embodiment including various vacuum ports 600 602 each with a different vacuum pressure these various vacuum ports 600 602 are collectively referred to as the housing vacuum channels 203 throughout this disclosure as described above pressurized air is pumped into the interface 208 through housing air channels 202 this housing air channel 202 is disposed furthest from the shaft 110 adjacent to the housing.