Hydraulic seals

Claim 2

A hydraulic fluid seal arrangement for sealing between first and second relatively movable members having complementary cylindrical working surfaces with a clearance gap therebetween, said members having first and second annular grooves axially spaced from each other, each of said grooves being juxtaposed to the working surface of the other of said mEmbers,said first annular groove being situated axially in between a fluid chamber and said second annular groove; a first annular seal situated in said first annular groove; a second annular seal situated in said second annular groove, said second annular seal being substantially more compressible under pressures less than a maximum working pressure than said first annular seal is compressible at said maximum working pressure, and said second annular seal having a coefficient of friction versus pressure characteristic which provides undesirably high friction at pressures above a predetermined pressure less than said maximum working pressure, whereby when said maximum working pressure exists in said chamber said first annular seal causes a pressure drop to maintain the pressure at said second annular seal less than said predetermined pressure.

Claim 3

A seal arrangement according to claim 1 wherein the cross-section of said second seal is less than the cross-section of said second annular groove, a first axial portion of said second seal having a radial thickness greater than the depth of said second groove and a second axial portion having a radial thickness no greater than said depth, said first axial portion being axially located in between said second axial portion and said first groove, whereby application of fluid pressure through said clearance gap to said second groove axially compresses said second seal in said second groove, and said second seal axially expands to force fluid back from said second groove through said clearance gap upon the reduction of pressure in said chamber.

Claim 4

A seal arrangement according to claim 1 wherein said first seal comprises a tetrafluorethylene fluorocarbon material and said second seal comprises polyurethane.

Claim 5

A seal arrangement according to claim 1 wherein said first and second relatively movable members comprise a bearing means and a cylindrical shaft, respectively, said shaft being adapted to rotate within said bearing means.

Claim 6

A seal arrangement according to claim 1 wherein said first and second grooves are axially spaced apart along an internal wall portion of said cylinder.

Claim 7

A seal arrangement according to claim 1 wherein said second annular seal has a generally U-shaped cross-section comprising a rear base portion from which a pair of lip portions extend generally axially toward said first annular seal, and ring means situated between said pair of lip portions.

Claim 8

A hydraulic fluid seal arrangement for sealing between first and second relatively movable members having complementary cylindrical working surfaces with a clearance gap therebetween, a first of said members having first and second annular grooves axially spaced from each other, each of said grooves being juxtaposed to the working surface of the second of said members, said first annular groove being situated axially in between a fluid chamber and said second annular groove, said fluid chamber communicating with said first annular groove; a first annular seal situated in said first annular groove, said second annular seal having a cross-section less than that of said second groove thereby providing an unfilled space in said second groove, said second annular seal being axially compressible into said unfilled space upon application of fluid pressure to said second groove thereby to admit fluid to said second groove, and expandable upon reduction of fluid pressure in said chamber to force fluid from said second groove through a portion of said clearance gap toward said first groove, wherein said second seal is substantially more compressible under pressures less than a predetermined pressure than said first seal is compressible at a maximum working pres-sure, said second seal having a coefficient of friction versus pressure characteristic which provides undesirably high friction at pressures above said predetermined pressure, said first seal providing a pressure drop from the pressure in said chamber to maintain the pressure applied to said second seal at a value Less than said predetermined pressure during normal operation.

Claim 9

A hydraulic fluid seal arrangement for sealing between first and second relatively movable members having complementary cylindrical working surfaces with a clearance gap therebetween, a first of said members having first and second annular grooves axially spaced from each other, each of said grooves being juxtaposed to the working surface of the second of said members, said first annular groove being situated axially in between a fluid chamber and said second annular groove, said fluid chamber communicating with said first annular groove; a first annular seal situated in said first annular groove, said second annular seal having a cross-section less than that of said second groove thereby providing an unfilled space in said second groove, said second annular seal being axially compressible into said unfilled space upon application of fluid pressure to said second groove thereby to admit fluid to said second groove, and expandable upon reduction of fluid pressure in said chamber to force fluid from said second groove through a portion of said clearance gap toward said first groove, wherein said second seal is substantially more compressible under pressures less than a predetermined pressure than said first seal is compressible at a maximum working pres-sure, said second seal having a coefficient of friction versus pressure characteristic which provides undesirably high friction at pressures above said predetermined pressure, said first seal providing a pressure drop from the pressure in said chamber to maintain the pressure applied to said second seal at a value Less than said predetermined pressure during normal operation.

Claim 10

A seal arrangement according to claim 7 wherein said first seal comprises a tetrafluorethylene fluorocarbon material and said second seal comprises polyurethane.