GB1474909A - Control valve arrangement for gas turbine engine fuel supply system - Google Patents

Abstract

1474909 Gas turbine engine fuel systems LUCAS INDUSTRIES Ltd 14 Oct 1974 [15 Nov 1973 26 Jan 1974] 53029/73 and 03748/74 Heading FIG [Also in Division G3P] A gas turbine engine fuel system includes a pump 11, variable metering device 12, and, downstream thereof, a valve arrangement 15 having a control element 25 movable in response to an increase in a servopressure signal to increase fuel flow through outlet 22 to engine 10, a pilot valve 29, 30 movable in response to an increase in a shaft speed responsive pressure signal derived by device 19 to decrease the servopressure signal, and means 37 responsive to an increase in an engine operating variable to decrease the servopressure signal by reducing the bias applied to pilot valve-member 30 by spring 36. Pump 11 is of positive displacement type the stroke of which is controlled by a spring- biased piston 16 subject on opposite sides to the pressures at the outlets of the pump and valve 15 respectively. Metering device 12 effects normal control of the engine in response to the position # of the throttle lever, the delivery pressures P 2 , P 3 of the low and high speed compressors and the speed NH of the high speed spool. A unit 13 responsive to the latter maintains the pressure drop across device 12 constant for a given speed. Valve 15 is an emergency device and during normal running the spool 25 thereof is held in the fully open position shown by the servopressure signal communicated to the lower end of the spool from the pump outlet via line 26 and restriction 27. Should the speed N H become excessive, the pressure signal in line 20 increases causing diaphragm actuator 32 to rotate pilot valve flapper 30 clockwise and thus open nozzle 29 to decrease the servopressure and cause spool 25 to move downwardly and reduce the fuel-flow. The latter is also reduced when a hinged abutment 34 is rotated clockwise, to reduce the bias of spring 36, by a torque motor 35 responsive to an electric signal derived by unit 37 when an excessive exhaust temperature T G or low speed spool speed N L is sensed. A feedback spring 33, opposed by spring 31, is disposed between spool 25 and flapper 30. A manual lever controlled shut-off valve 23 having a spool 45 is disposed downstream of valve 15. In the shown position 'A' of the lever, fuel flow is permitted from outlet 22 via line 24 to the main engine burners and also to the pilot burners via lines 41, 42 from the downstream side of metering device 12. In the starting position 'B', the downstream side of pump 11 is connected via line 26, restrictors 27, 43 and bore 44 to the main burner line 24. Line 41 remains connected to pilot burner line 42. In the shut position 'C', outlet 22 is blocked and connection 46 is opened to allow fuel in lines 24, 42 to escape to drain. In a modification Fig. 3 (not shown) the spool (71) of the shut-off valve does not itself in position 'C' block the fuel outlet 22 but acts as a pilot valve to vent the servopressure from below spool 25 so that the latter closes. In a further modification Fig. 2 (not shown), the shut-off valve comprises three control members (52, 53, 54) which are manually rotatable in unison.