Patent ID: 8388742

Claim:
An apparatus comprising: a) a membrane having an input surface, an output surface and a peripheral edge; b) a housing including a pair of mating flanges supporting the membrane, one flange being an input flange and the other flange being an output flange, the input flange and the input surface of the membrane cooperating to define a gas input space, the housing having a test gas inlet that communicates with the gas input space, the output flange and the output surface of the membrane cooperating to define a gas outlet space, the housing having a test gas outlet that communicates with the gas output space; wherein the improvement comprises: an inner seal and an outer seal mounted between the input and the output flanges, the inner seal being disposed closer to the peripheral edge of the membrane than the outer seal, the input flange and the output flange cooperating to define an annular space therebetween, the annular space being disposed between the inner and the outer seals, and a purge gas inlet line and a purge gas outlet line both connected to the annular space.