GB834923A - Improvements in or relating to sealing means - Google Patents

Abstract

834,923. stuffing-box substitutes. ROLLSROYCE Ltd. Jan. 21, 1958 [Jan. 25, 1957], No. 2876/57. Class 122 (5). Sealing means between the shaft 12, Fig. 1, of a gas-turbine and its housing 10 comprises a sealed sleeve 28 mounted on the housing and encircling the shaft with a small clearance space which at one end communicates with the turbine chamber 18 and at the other with a liquid delivered at a higher pressure than that of the gas in the chamber 18, and helical grooving 26 formed in one of the surfaces bounding the clearance space. As shown in Fig. 1, the sleeve 28 surrounds a second sleeve 19 fixed to the shaft 12 and is connected to one end of a bellows 29, which, at its other end, is attached to a member 30 mounted in the housing 10, the surface of the sleeve 19 being formed with the grooves 26. The sleeve 28 is formed with a radial surface 32 which, when the shaft is stationary or running at slow speed, is urged into contact with a ring 20 mounted on the shaft 12 by the pressure of the gas, such as helium, contained within the chamber 18. In operation under normal running conditions, liquid, such as oil, is fed by a pump 35 through a pipe 36 into a chamber 34 at a higher pressure than that of the gas and thereby moves the surface 32 away from the ring 20 until a flange 33 abuts the member 30 so that liquid then tends to flow into the clearance space between the two sleeves 19, 28. The dimensions of the clearance space and the dimensions and handing of the grooves 26 are so selected that the oil drops in pressure as it moves towards the chamber 18 and the gas, which tends to leak from the chamber, rises in pressure until at a certain point between the ends of the sleeve 28 an oil/gas interface is formed. In order that the seal may be independent of variations in gas pressure in the chamber 18, a constant high-pressure gas supply may be admitted through a duct 24. The sleeve 19 is provided with a finger 21 which rotates in a groove 22 formed in the housing 10 so that any gas contaminated with oil vapour is discharged through an outlet 23. In the modification shown in Fig. 3, the oil-pump 35 is dispensed with and oil supplied to a bearing 16 is pressurized by means of helical grooves 41 formed in the surface of the main shaft 14, of opposite hand to the grooves 26. The grooves, in co-operation with a sleeve 40 surrounding the grooved surface, pump the oil into the chamber 34a to act upon the flange 33 in the manner previously described. To prevent any build-up of excessive pressure in the latter chamber, a relief valve 58 is located in a duct 57 leading to an oil drain and is urged into the closed position by a spring 59 and the pressure of the gas in the chamber 18 acting upon a diaphragm 62. A spring-urged rubbing-collar type seal 51a is mounted on a spherical seating 50 formed on the sleeve 40, although, in a further modification, this seal may be replaced by a bellows.