Patent ID: 7144016

Claim:
A gas seal assembly for sealing between a rotating shaft and a surrounding casing, the gas seal assembly comprising: a pair of sealing members, of which a first sealing member is mounted for rotation with a rotating shaft and a second sealing member is secured to a casing, each of the first sealing member and the second sealing member having an active face adjacent to a gap between the members which gap constitutes a leakage path through a seal assembly, one of the members being arranged in use to be urged in a direction attempting to reduce a width of the gap so as to prevent escape of a processed gas from a high pressure side of the seal assembly to a low pressure side; and a gas bleed arrangement for allowing the processed gas from the high pressure side of the seal assembly to be admitted into the gap at a position radially between inner and outer diameters of the sealing members to create a gas pressure in the gap applying a force in a direction to increase the width of the gap, wherein the gas bleed arrangement includes a bleed channel passing axially through the first sealing member between the active face of the first sealing member and another face of the first sealing member opposite the active face, which bleed channel has an associated flow resistance and is dimensioned such that the gas pressure at a gap end of the bleed channel is reduced relative to the pressure of the processed gas at the high pressure side of the seal assembly and such that the gas pressure in the gap decreases as the gap width increases, wherein the first sealing member includes a front annular member and a rear annular member, a front surface facing the gap being formed on the front annular member, and a rear surface of the front annular member facing a front surface of the rear annular member, a radially extending portion of the bleed channel being formed in one or both of the front surface of the rear member and the rear surface of the front member.