Pressure balanced circumferential seal assembly

Claim 2

A circumferential seal assembly adapted for mounting in a housing and around a shaft passing through said housing for sealing against the passage of high fluid pressure along said shaft from an upstream to a downstream side of said housing, said assembly comprising: a first annular shoulder adjacent said downstream side of said housing and a second annular shoulder spaced from said first shoulder along said shaft adjacent said upstream side defining an annular cavity within said seal assembly surrounding said shaft and in fluid communication with said downstream and upstream sides of said housing through first and second annular spaces defined by said first and second shoulders respectively with said shaft; a segmented primary seal ring between said first and second shoulders and having a downstream surface portion in sealing engagement with said first shoulder and an inner surface in sealing engagement with said shaft; a backup ring between said primary ring and said second shoulder in sealing engagement with said primary ring; a first annular fluid-tight resilient means connected to said backup ring and said second shoulder for urging said backup ring against said primary ring, and for urging said primary ring against said first shoulder to maintain the same iN static sealing engagement, and for forming a first fluid path for directing said high pressure against an upstream and downstream surface portion of said backup ring; a second annular resilient means in engagement with the outer circumference of said primary ring urging said primary ring into dynamic sealing engagement with said shaft for sealing against the passage of said high fluid pressure from said upstream side to said downstream side of said housing along said shaft; said backup ring defining a third annular space with said shaft for directing said high pressure from said first fluid path against both an upstream and a downstream surface portion of said backup ring to provide opposed counterbalancing fluid forces acting axially on said backup ring and for directing said high pressure against an upstream surface portion of said primary seal ring; and a second fluid path formed in said first shoulder in fluid communication with said upstream side for directing said high fluid pressure against said downstream surface portion of said primary seal ring to provide a counterbalancing fluid force axially opposing said high pressure acting on said upstream surface portion of said primary seal ring; whereby said primary seal ring remains substantially axially balanced regardless of changes in differential pressure between said upstream and downstream sides of said housing.

Claim 3

A circumferential seal assembly adapted for mounting in a housing and around a shaft passing through said housing for sealing against the passage of high fluid pressure along said shaft from an upstream to a downstream side of said housing, said assembly comprising: a first annular shoulder adjacent said downstream side having an inner circumferential face spaced from said shaft to permit the passage of low fluid pressure therebetween; a second annular shoulder adjacent said upstream side and spaced from said first shoulder along said shaft and having an inner circumferential face spaced from said shaft to permit the passage of high fluid pressure therebetween; a segmented primary seal ring having: a downstream side-face bearing axially against said first shoulder thereby forming a first static sealing interface therewith and an upstream side-face opposite said downstream side-face, and an inner circumferential face bearing against said shaft thereby forming a dynamic sealing interface therewith and an outer circumferential face substantially opposite said inner face, said outer face having a first face portion for communication with low fluid pressure on the downstream side of said housing and a second face portion for communication with high fluid pressure on the upstream side of said housing; a backup ring between said primary ring and said second shoulder having: a downstream side-face bearing axially against said seal ring upstream side-face thereby forming a second static sealing interface therewith and an upstream side-face substantially opposite said downstream side-face, and an inner circumferential face radially spaced from said shaft and axially spaced from the second face portion of said sealing ring for directing said high pressure against a part of said second face portion, and an outer circumferential face substantially opposite said inner face for communication with said low pressure; a first biasing means connected to both said upstream face of said backup ring and said second shoulder in fluid-tight connection to form a first fluid path for directing said high pressure against the upstream and downstream faces of said backup ring and against the second face portion of said seal ring and for urging said backup ring against said seal ring, said first biasing means proportioned to exert a predetermined seating force for maintaining said first and second sealing interfaces in sealing engagement; a second biasing means urging said sealing ring against said shaft for maintaining said dynamic sealing interface in sealing Engagement; and a second fluid path formed in said first shoulder in fluid communication with said high fluid pressure and with said first interface for directing said high pressure against the downstream side-face of said seal ring to substantially counteract the high fluid pressure acting against the upstream face of said seal ring, whereby said predetermined seating force between said mating surfaces of said first sealing interface will remain substantially constant regardless of the pressure differential between said high and low pressure.

Claim 4

A circumferential seal assembly adapted for mounting in a housing and around a shaft passing through said housing for sealing against the passage of high fluid pressure along said shaft from an upstream to a downstream side of said housing, said assembly comprising: a first annular shoulder adjacent said downstream side having an inner circumferential face spaced from said shaft to permit the passage of low fluid pressure therebetween; a second annular shoulder adjacent said upstream side and spaced from said first shoulder along said shaft and having an inner circumferential face spaced from said shaft to permit the passage of high fluid pressure therebetween; a segmented primary seal ring having: a downstream side-face bearing axially against said first shoulder thereby forming a first static sealing interface therewith and an upstream side-face opposite said downstream side-face, and an inner circumferential face bearing against said shaft thereby forming a dynamic sealing interface therewith and an outer circumferential face substantially opposite said inner face, said outer face having a first face portion for communication with low fluid pressure on the downstream side of said housing and a second face portion for communication with high fluid pressure on the upstream side of said housing; a backup ring between said primary ring and said second shoulder having: a downstream side-face bearing axially against said seal ring upstream side-face thereby forming a second static sealing interface therewith and an upstream side-face substantially opposite said downstream side-face, and an inner circumferential face radially spaced from said shaft and axially spaced from the second face portion of said sealing ring for directing said high pressure against a part of said second face portion, and an outer circumferential face substantially opposite said inner face for communication with said low pressure; a first biasing means connected to both said upstream face of said backup ring and said second shoulder in fluid-tight connection to form a first fluid path for directing said high pressure against the upstream and downstream faces of said backup ring and against the second face portion of said seal ring and for urging said backup ring against said seal ring, said first biasing means proportioned to exert a predetermined seating force for maintaining said first and second sealing interfaces in sealing engagement; a second biasing means urging said sealing ring against said shaft for maintaining said dynamic sealing interface in sealing Engagement; and a second fluid path formed in said first shoulder in fluid communication with said high fluid pressure and with said first interface for directing said high pressure against the downstream side-face of said seal ring to substantially counteract the high fluid pressure acting against the upstream face of said seal ring, whereby said predetermined seating force between said mating surfaces of said first sealing interface will remain substantially constant regardless of the pressure differential between said high and low pressure.

Claim 5

The seal assembly of claim 2 wherein: said upstream face of said backup ring is proportioned so that the axial force caused by said high pressure acting directly against it is substantially equal and opposite to the sum of the axial forces caused by said high pressure acting directly against a portion of said downstream face of said backup ring and by said high pressure acting indirectly against said backup ring at said second static interface; whereby said backup ring remains substantially axially balanced regardless of changes in differential pressure between said upstream and downstream sides of said housing; and wherein said first biasing means is proportioned to exert a predetermined seating force urging said backup ring against said primary seal ring to maintain said rings in substantially constant static sealing relation at said second sealing interface regardless of changes in differential pressure between said upstream and downstream sides of said housing.

Claim 6

The seal assembly of claim 3 wherein: said downstream side-face of said primary seal ring is proportioned so that both the axial force caused by said high pressure acting directly against said first sealing interface from said second fluid path and the axial force caused by said high pressure acting indirectly against said primary seal ring at said first static interface is substantially equal and opposite to the sum of the axial forces caused by said high pressure acting directly against both a portion of said upstream side-face of said primary seal ring and by said high pressure acting indirectly against said primary seal ring at said second static interface, whereby said primary seal ring remains substantially axially balanced regardless of changes in differential pressure between said upstream and downstream sides of said housing; and wherein said predetermined seating force exerted against said backup ring urges said primary seal ring against said first shoulder to maintain a substantially constant sealing pressure between said rings and said shoulder at said first and second interfaces regardless of changes in differential pressure between said upstream and downstream sides of said housing.

Claim 7

The seal assembly of claim 4, wherein: said inner circumferential face of said primary seal ring includes a first inner face portion having a larger diameter than said shaft and in communication with said low pressure and further includes a second inner face portion having a diameter substantially the same as said shaft forming said dynamic sealing interface for separating said low pressure from said high pressure along said shaft; said first shoulder includes a third fluid path formed therein for directing said low fluid pressure in communication with said annular cavity and surrounding said first face portion of said outer face of said primary seal ring; said first inner face portion proportioned so that said lower pressure acting radially outwardly thereon is substantially equal and opposed to said low pressure acting radially inwardly on said first face portion of said outer face of said primary seal ring; said second face portion of said outer face of said primary seal ring is radially opposite said dynamic sealing interface and in communication with said high pressure; and said second face portion proportioned so that said high pressure acting directly thereon is substantially equal and radially opposed to said high pressure acting indirectly on said dynamic sealing interface, whereby said primary seal ring remains substantially radially balanced regardless of changes in differential pressure between said upstream and downstream sides of said housing, said second biasing means exerting a predetermined seating force against said outer face portion of said primary seal ring thereby urging said second inner face portion against said shaft for maintaining a constant sealing pressure at said dynamic sealing interface regardless of changes in differential pressure between said upstream and downstream sides of said housing.

Claim 8

The apparatus of claim 5 wherein: the segments of said segmented primary seal ring each include a male and female end, said male end of one segment mating with a corresponding female end of an adjacent segment, each of said female ends including a relief formed in said second inner face portion for reducing the area against which said high pressure acts indirectly against said face to compensate for radial forces tending to lift said segments away from said shaft at the intersection of said male and female ends.