GB1309865A - Combined static and fluid selas - Google Patents

Abstract

1309865 End face seals ENGLISH ELECTRIC CO Ltd 4 Jan 1972 [22 Jan 1971] 2974/71 Heading F2B A seal for the shaft 1 of a gas-cooled alternator, gas circulator or compressor comprises first and second sealing surfaces 25, 13 each cooperating with a common sealing surface 7 of the shaft, means, such as spring bellows 33 and the pressure of the working gas, for urging the second sealing surface towards engagement with the shaft sealing surface, and a pressure fluid system (oil) which is operable when the shaft is rotating to provide a pressure fluid layer 32 between the first sealing surface and the shaft sealing surface while simultaneously preventing engagement of the second sealing surface and which can be made inoperative when the shaft is stationary to destroy the fluid layer and allow the second sealing surface to make a static seal. The second sealing surface is provided by seal ring 13 formed of P.T.F.E., aluminium, silver or synthetic rubber mounted in an annular piston 9, 10, 11. The bellows 33 for urging the piston out of engagement is supported on a ring 34 secured to the housing. The first sealing surface 25 is provided on a seal ring unit 23, 24 sealed to the piston by inner and outer bellows 20, 21. The pressure fluid is supplied through passages 3 and slidable connecting tubes 18 to the space 26 between the bellows where it acts on a surface 40 of the piston to disengage it from the shaft sealing surface 7 and passes through passages 29, 30, 31 to form the fluid layer 32. This escapes radially outwards to a chamber 5 for feed back to the supply system and radially inwards for feed back through a primary drain 35 via holes 35A and space 4, a secondary drain 36 being provided for returning oil which has escaped radially inwards into the clearance gap between the shaft 1 and a gland surface 39. The latter is grooved helically to provide a pumping effect. Upon shut down, the oil pres- sure is cut off after the shaft 1 has come to rest so that the fluid layer 32 is destroyed and the piston 9, 10, 11 moves under the action of the spring bellows 33 and gas force to engage the seal ring 13 on the shaft sealing surface 7. In a second embodiment, Fig. 2 (not shown), the spring pressure on the annular piston (55) is provided by coil springs (58) instead of a bellows and the seals between the piston and housing and between the piston and the seal ring unit 61, 66 are provided by 0-rings instead of the bellows.