GB1174207A - Improvements in or relating to fluid flow machines - Google Patents

Abstract

1,174,207. Turbines; gas turbine plant. ROLLS-ROYCE Ltd. May 30, 1968, No.25922/68. Headings F1G and F1T. [Also in Divisions F2 and G3] Apparatus for controlling the axial gap between a fixed structure and an axially movable rotatable structure of a fluid-flow machine comprises fluidpressure means responsive to changes in a supply pressure and controlling a power source capable of producing relative axial movement between the fixed and rotatable structures, the supply pressure being fed to the fluid-pressure means from a chamber bounded by the structures via an orifice which is closable by a part of the rotatable structure so as to vary the supply pressure in dependence on the size of the gap. When applied to a gas turbine engine to maintain constant the axial clearance "A" between the tips of the turbine rotor blades 22 and part of the housing 21, the invention includes a chamber 20 bounded by a heat shield 18 and pressurized by air from the engine compressor. Axial and radially extending seals 30, 32 maintain the air pressure in chamber 20. An annular flange 26 on an extension 28 of the turbine disc 10 co-operates with a pad 34 secured to heat shield 18, the size of the axial gap between the flange and pad determining the rate of leak-off of air from chamber 20 to a duct 36, 38 and hence the pressure in the duct. The latter is connected to a chamber 40 on one side of a spring loaded diaphragm 44 attached to a spool valve 50 slidable in a bore 52 in a housing 54. A hydraulic pump 68 supplies fluid through a pipe 70 to an inlet port 60 of the bore 52 and, according to the position of spool valve 50, the fluid may pass to one or other of pipes 74, 76, leading to opposite sides of an annular piston 78 slidable in a fixed cylinder 80. The piston 78 is attached to the outer race 82 of a bearing 84, the inner race 86 of which is mounted on the shaft 14 connecting the turbine 10 to the high-pressure compressor (6, Fig.1, not shown), of the engine. Thus any change in pressure in duct 38 as a result of a departure from the desired value of the axial gap causes adjustment of the spool valve 50 and axial movement of bearing 84 and shaft 14 to restore the gap to its desired value. In a modification, the piston 78 is fixed and cylinder 80 movable and attached to shaft 14.