GB1248198A - Sealing device - Google Patents

Abstract

1,248,198. Turbines; gas turbine plant. ROLLS-ROYCE Ltd. Feb. 6, 1970, No.5872/70. Headings F1G and F1T. [Also in Division F2] A sealing device for maintaining constant the clearance 7 between two relatively movable portions comprises, when applied to the turbine 2 of a gas turbine engine, means for varying the temperature of gases directed in heat exchange relationship with the stator casing 6 so as to compensate for relative expansion or contraction of the turbine rotor and casing 6. The means comprises four equiangularly spaced air pipes 10 each having an outlet 11 opposite the shrouds 12 of the rotor blades 3. Each pipe 10 communicates via a restriction 13 with a common supply pipe 14 receiving air bled from the engine compressor, the downstream side of restriction 13 connecting via passage 17 with the space below a diaphragm 16 mounted in a chamber 15. The space above diaphragm 16 is vented via pipe 20 and restriction 23 to a pressure which varies with a pressure adjacent the turbine 2. Should the rotor blades 3 expand to a greater extent than casing 6, the size of the clearance 7 between sealing ribs 4 and honeycomb 5 decreases causing a rise in pressure at the outlet ends 11 of pipes 10. The pressure beneath diaphragm 16 thus increases forcing the latter and an attached link 24 upwards to act on a servo device 38 which causes a lever 33 to pivot about a fixed fulcrum 34. The lever 33 is connected to butterfly valves 25, 26 disposed respectively in a duct 27 receiving hot turbine exhaust gases and in a duct 28 receiving cooler air from the compressor. Valve 25 thus opens further and valve 26 closes further to increase the temperature of the gaseous mixture in common manifold 41, the mixture flowing through passages 42, 43 in heat exchange with casing 6 so as to heat the latter causing it to expand and restore the clearance 7 to the desired value. The casing 6 may be divided into four equal segments each of which is separately heated or cooled in dependence upon the pressure in the respective pipe 10 so as to cater for any eccentricity between the casing and the turbine rotor.