Patent GB-688546-A (GB)
Title: Improvements in or relating to fuel feeding systems more particularly for gas turbine engines
IPC: F02C9/28
Filed: 1950-01-13
Abstract: 688,546. Gas turbine plant. BENDIX AVIATION CORPORATION. Jan. 13, 1950 [Feb. 3, 1949], No. 943/50. Class 110(iii) [Also in Group XXIX] A fuel supply system for gas turbine engines on air-. craft comprises a fuel control device, Fig. 4, having in series in a fuel conduit a throttle valve 101 varying the area of a metering restriction mounted in said conduit and a regulator valve 90 for controlling the metering head across the restriction in response to an operating condition of the engine, e.g. speed, an enginedriven variable displacement pump, 25, Fig. 1, for supplying fuel under pressure to the control device having a pump control element movable to positions to vary the effective pump stroke at a given pump speed and means 215, Fig. 3, responsive to the pressure differential between the fuel pressure at a point upstream of the regulator valve and the metered fuel pressure at a point beyond the throttle valve, for automatically positioning said element. As shown, the burner nozzles 18 of a gas turbine 10 are fed through pipes 188. 192 from a fuel control device 76 fed from two variable stroke swashplate pumps 25, 25' driven from the turbine. The fuel control device 76 contains a governor operated valve 101, a pressure regulating valve 90, a valve 195 for maintaining a constant pressure drop across the valves 90, 101 together, an emergency throttle valve 270, a normally open change-over valve 260 and a normally closed change-over valve 266, a filter 78 with a by-pass relief valve 80 and a pump control unit 215. The control device 76 has a delivery pipe 170 connected to a further unit 171 comprising a shut-off valve 172 and a valve 185 to supply secondary burner passages. Each pump 25, Fig. 2, comprises a cylinder block 30 driven from the turbine through a spline 32 and a swash-plate 35 angularly adjusted by a spring- loaded piston 45 exposed to the pump discharge pressure through a passage 50 on one side and through a restriction 51 on the other side. The chamber 46 on the spring side of the piston may be vented to reduce the output of the pump by leakoff valves 57, 291. The valve 57 is carried by a lever 55 operated by a diaphragm 60 which is loaded by an adjustable spring 68. The diaphragm 60 is subject to the difference between the pump inlet pressure in a chamber 61 and a pressure corresponding to the speed of the turbine in a chamber 62 fed from a radial passage 72 in the pump block 30. The valve 291 is closed against a spring 292 by a solenoid 295. The pumps are also controlled through the pipes 225 by the pump control unit 215 which has a hinged leak-off valve 219 closed by a spring 250. The governor valve 101, Fig. 4, comprises a ported cylinder slidable in a ported sleeve 103 and is actuated through a rod 107 by centrifugal weights 117 driven from the turbine through a spline 124. The valve 101 is closed against a loading spring 111 adjusted by the pilot through an arm 113. The spring abutment 112 slides on a stop rod 108 determining the minimum flow. Metered fuel passes into the annulus 106 and out to the delivery pipe 170 past a flap valve 165. The pressure regulating valve 90, Fig. 4, comprises a ported cylinder moving in a ported bushing 92 and connected by a stem 95 to a diaphragm 94 exposed to the unmetered fuel pressure P<SP>2</SP> in a chamber 89<SP>1</SP> and to the pressure P<SP>3</SP> in a chamber 161 fed from the chamber 89<SP>1</SP> through jets 160. Fuel in the chamber 161 passes to the annulus 106 through a restriction 159 and a passage 164. The restriction 159 is adjusted by a needle valve 157 to compensate for changes in air density. The valve 157 is operated through lever arms 151, 156 on a shaft 152 by a spring loaded bellows 146 responsive to changes of pressure and temperature of the air at the compressor or ram inlet. The valve 90 is operated through a lever 134 connected to a sleeve 133 slidable on the sleeve 103 of the governor valve and displaced by turbine driven centrifugal weights 130. The valve 90 operates to maintain the metering head across the governor valve as a function of engine speed. This head is however compensated for changes in air density by the needle valve 157. The lever 134 which has a bifurcated end 137 operates on the regulator valve stem 95 through two telescopic members 138, 139, Fig. 10, with a spring 140 between them. At speeds below a predetermined value, the fork 137 acts through the spring 140 on the stem 95 and the metering head is maintained at a substantially constant value determined by a spring 100. The opening of the regulator valve 90 is limited by an adjustable screw 143. The valve 90 is by-passed by a passage 256 and an orifice 255 controlled by a needle valve. The latter is adjusted to have an effective flow area less than that of the governor valve when against its stop 108 and permits a fuel flow uncompensated for density changes during idling at high altitude. The shut-off valve 172, Fig. 4, is balanced as regards inlet pressure when closed. In this position fuel passes to the pump suction 40 through ports 175 and a conduit 177. The valve is operated through rack and pinion mechanism 179, by a lever 182, Fig. 1. The valve 185 is loaded by a spring 186 and opens to admit fuel to secondary and larger burner passages through the pipe 192 and a header 193 when the pressure of the metered fuel exceeds a predetermined value. The "constant pressure drop" valve 195, Fig. 3, comprises a ported hollow cylinder movable in a ported bush 196 under the control of a spring loaded diaphragm 198 separating chambers 199, 200 connected through a restriction by passages 201, 202. The valve 195 itself is balanced but the pressure p<SP>4</SP> of the metered fuel acts in the chamber 200 through a passage 212 with a restricted orifice 212<SP>1</SP>. The pressure P<SP>1</SP> on the .inlet side of the regulator valve 90 acts in the chamber 199. Movement of the spring abutment 206 in the valve opening direction limited by-an adjustable nut 209. The leak-off valve 219 of the pump control unit 215 is operated by a rocker arm 216 acted on by plungers 231, 246. The leak-off valve 219 tends to close and so increase the pump output under the action of the metered fuel pressure P<SP>4</SP> on a diaphragm 245. The pump outlet pressure p<SP>0</SP> acting, through a choke 239 comprising a set of spaced apertured discs, on a diaphragm 230 tends to open the valve 219 and so reduce the pump output. The emergency throttle valve 270, Fig. 3, is operated through rack and pinion mechanism 275 by a lever 279 coupled for simultaneous operation with the pilot operated lever 113, Fig. 4. For idling, the valve 270 is by-passed by passages 288, 289 controlled by a needle valve 285. Fuel from the emergency throttle passes via a pipe 280 and a flap valve 282, Fig. 4. to the pipe 170 and holds the flap valve 165 closed. The change-over valves 260, 266 are operated simultaneously by solenoids 262, 268 respectively, these being in circuit with a pilot-operated switch controlling the energisation of the pump solenoid valves 290. 290<SP>1</SP> and also in circuit with a pressureactuated switch 317, Fig. 4, which closes when the metered fuel pressure acting through a pipe 320 falls below a minimum value. In these circumstances, the valve 260 is closed and the valve 266 is opened. The pilot operated switch has a take-off position in which only the solenoids of the valve 290, 290<SP>1</SP> are energised, a neutral position, and an emergency position in which the solenoids 262. 268, are also energised whether the pressureactuated switch is closed or open. A signal light also indicates that the emergency system is in operation. Reference has been directed by the Comptroller to Specification 577,016, [Group XXIX].