Patent GB-1275775-A (GB)
Title: Improvements in or relating to fluid flow machines
Inventor: GILBERT RONALD ALBERT
IPC: F01D11/02
Filed: 1969-09-26
Abstract: 1275775 Bearings; hydraulic dashpots ROLLS-ROYCE Ltd 26 Sept 1969 47613/69 Headings F2A and F2S [Also in Divisions F1 and G3] Apparatus for controlling the axial gap between a fixed structure and an axially movable rotatable structure of a fluid flow machine includes a fluid pressure supply variable in dependence upon the size of the gap and controlling a valve of a power source capable of producing relative axial movement between the structures, the valve having damping means operable to damp movement of the valve to a greater extent when the valve is moving in one direction than when the valve is moving in the opposite direction. The apparatus operates in similar fashion to that described in Specification 1,174,207 and is applied to a gas turbine engine to maintain constant the gap "A" between the tips of the turbine rotor blades 22 and the nozzle blade support ring 36 and between labyrinth sealing elements 26, 30 and adjacent stator structure 28, 32. The apparatus includes valve control mechanism having a casing 44 containing an annular bellows 62 biased to the left by a coil spring 64. The casing 44 has three fluid connections 46, 48, 50 for pipes 38, 40, 41 and each connection has an orifice 52, 54, 56 respectively. Pipe 38 opens at its other end in close proximity to the sealing element 26 so that the pressure in the pipe varies with variation in the gap "A". Pipe 40 however opens some distance from element 26 so that the pressure therein is unaffected by the gap "A". Pipe 41 is connected to the high pressure compressor to provide an amplifying pressure. The interior of bellows 62 is connected to the variable pressure in pipe 38 via duct 47, chamber 63 and openings 65. Should the gap "A" decrease, for example, the pressure in pipe 38 increases causing the bellows 62 and its spindle 66 to move to the left until the pressure across orifice 54 is balanced. This movement causes a lever 74 mounted on two arms 76 to pivot in an anticlockwise direction to force the spindle 82 of a spool valve 84 to the right. Hydraulic fluid from a swash plate pump 114 thus flows from valve inlet 124 to outlet 128 and through duct 136 to the left side of a piston 148 mounted in a fixed cylinder 150. The piston 148 is therefore forced to the right taking with it a pair of ball bearings 140 and the turbine shaft 14 supported thereby so as to restore the gap "A" to the desired value. The valve spindle 82 has a damping device comprising a casing 88 and two flexible diaphragms  92, 94 attached to opposite ends of the casing to define chambers 97, 99 separated by a central wall having an aperture 102. A spindle 100 attached to the end of valve spindle 82 passes through aperture 102 and is secured to dia. phragms 92, 94, a spring 104 bearing on a fixed abutment 108 biasing spindle 100 to the left. A duet 132 enables hydraulic fluid to flow from outlet 130 of valve 84 past valve 113 to the chambers 97, 99, the chamber 97 having an exhaust port 112. Thus when the valve spindle 82 is moved to the right to cause correction of a too small gap "A" there is little damping effect as the hydraulic fluid can escape from chamber 97 through port 112. The spindle 82 can therefore move rapidly to increase the gap. However should the spindle 82 be moved to the left to decrease an excessive gap "A" the spindle can only move slowly since it is damped by the hydraulic fluid forced through aperture 102 from chamber 99. The piston 148, shaft 14 and rotor disc 10 are thus moved slowly to the left to decrease the gap "A" without risk of overrun and consequent rubbing.