Reactor coolant pump hydrostatic sealing assembly with externally

Abstract

A pump having a shaft and housing containing pressurized system fluid variable between low pressure at pump startup and high pressure at pump operation, employs a hydrostatic sealing assembly for sealably and rotatably mounting the shaft within the housing. In the assembly, both a runner mounted around the shaft for rotation therewith and a seal ring mounted to the housing have facing surfaces between which pressurized system fluid creates a flowing low pressure fluid film which prevents contact between the facing surfaces so long as a predetermined minimum leakrate is maintained therebetween. First and third seal ring surfaces face in opposite directions with the second surface facing in the same direction as faced by the seal ring facing surface. First and second chambers are defined contiguous to the first and second surfaces with the first chamber in communication with pressurized system fluid and isolated from the second chamber and with the latter isolated from the runner and seal ring facing surfaces. Pressurized balance fluid provided to the second chamber via a passage through the housing from the exterior thereof is at a balance pressure greater than the supply pressure of the system fluid such that the balance pressure is effective at pump startup when the supply pressure is low, and ineffective at pump operation when the supply pressure is high, to counter a seating force imposed on the seal ring first surface by the supply pressure and augment a lifting force imposed on the seal ring facing surface by the supply pressure so that at both pump startup and operation leakrates are produced between the runner and seal ring facing surfaces which are above the predetermined minimum.