Patent ID: 8899593

Claim:
An intershaft seal for inner and outer coaxial shafts which rotate relative to each other, the seal being located in an annular space between the shafts and maintaining an axial pressure differential between a fluid pressure on a first side of the seal and a different fluid pressure on a second side of the seal, the seal comprising: first and second runners which project into the annular space from a first one of the shafts and extend circumferentially around the first shaft such that a cavity is formed between the runners; a sealing ring which is coaxial with the shafts and is located in the cavity, the sealing ring having first and second axially spaced end faces, the first runner forming a first annular sealing interface with the first end face of the sealing ring and the second runner forming a second annular sealing interface with the second end face of the sealing ring, the sealing ring further making sealing contact with the second of the shafts to maintain the pressure differential; and a fluid path that extends from (i) a side of one of the runners that is adjacent to the cavity formed between the runners, (ii) through a wall of the first shaft, and (iii) to a side of one of the runners that is adjacent to a region of pressure which is intermediate to the pressures on the first and second sides of the seal, the fluid path allowing the cavity to adopt the intermediate pressure, wherein one of the runners is spring-loaded such that it is axially sliding sealing contact with the first shaft and urged towards the sealing ring.