Patent GB-1368875-A (GB)
Title: Shaft seal
IPC: F16J15/40
Filed: 1972-05-22
Abstract: 1368875 Shaft seals THERMO ELECTRON CORP 22 May 1972 [28 May 1971] 23908/72 Heading F2B A shaft seal for sealing the crank-shaft 10 of an expander in a Rankin cycle system or a turbine or pump shaft comprises a first sealing means 18 mounted on the shaft and presenting first and second sealing areas to mating sealing areas of a second sealing means 26, 26<SP>1</SP> mounted on a casing wall through which the shaft extends, and means 62 for applying, to buffer fluid within a compartment 48, a pressure which is equal to or greater than the pressures in either of the zones on each side of the shaft seal. As shown, the expansion chamber 186 is used to drive pistons 212, 214 within a crankcase 201 containing lubricant and leakage of working fluid past the pistons. During operation, the pressure in the crankcase varies from levels above to below the atmospheric pressure outside the crankcase and the buffer fluid in the compartment 48 surrounding the shaft seal is maintained to at least that of atmosphere by the pressure source 62 which is connected to atmosphere through parts 100 and to the crankcase through a pipe 104. In detail in Fig. 4, the pressure source 62, which is responsive to both atmospheric pressure and the pressures within the crankcase, consists of a buffer fluid reservoir 72 formed between diaphragm pistons 78, 80 and provided with a pipe 64 for connection to the buffer fluid compartment 48, the diaphragm piston operating between stops 96, 98 when subjected to atmospheric pressure through ports 100 and crankcase pressure through pipe 104. The buffer fluid is circulated by providing a compartment 48 which is eccentric to produce a pumping action or a pump in the pipe-line, cooled by circulation through a cooling loop 55 and replenished when required as shown by the indicator 108 on the top of the pressure source. Compression springs 88, 92 may be provided to apply an initial pressure to the buffer fluid. The shaft seal shown is of the end-face type in which two carbon rings 30, 30<SP>1</SP> are pressed towards one another by coil springs 34, 34<SP>1</SP>, and contact a steel or cast iron ring 18 mountsd on the drive shaft 10; alternatively, Fig. 5 (not shown), a pair of carbon rings (120) mounted on the shaft are urged apart by a coil spring into contact with rings (110) mounted on the casing, the buffer fluid chamber (112) being formed eccentrically around the seal to cause the required circulation. Alternatively, the pressure source (62) Fig. 6 (not shown), may simply be a single diaphragm (140), one side of which contains the buffer fluid while the other is connected to a gas pressure source independent of the pressures on each side of the shaft seal. In a further alternative, Fig. 7 (not shown), the pressure source (62) consists of two diaphragm pistons (162, 168) mounted in tandem to apply pressure to the buffer fluid in the reservoir (160), the space between the pistons being connected to the crankcase through a pipe (104) and containing a compression spring which acts only on the lower piston adjacent the reservoir while the space above the upper piston is connected to a.tmosphere through ports (156); when the pressure between the pistons is greater than atmospheric pressure, the pistons are urged apart but when this pressure is lower than atmospheric the pistons are coupled together to act downwardly upon the buffer fluid to apply a pressure in addition to that applied by the spring. In Fig. 10 (not shown) the shaft seal (11) is applied to a turbine shaft.