Patent GB-1259772-A (GB)
Title: Fuel control systems for gas turbine engines
Inventor: BLOOM JOSEPH LEWIS
IPC: F16K31/44
Filed: 1967-12-08
Abstract: 1,259,772. Gas turbine engine fuel systems; axial-flow compressors. JOSEPH LUCAS (INDUSTRIES) Ltd. March 6, 1969 [Dec. 8, 1967], No. 55856/67. Headings F1C and F1G. A gas turbine engine fuel system comprises a first throttle valve incorporating an orifice and a blade control member movable by means of a device sensitive to air-pressure variations at the engine compressor, a second throttle valve connected in series with the first one, and incorporating an orifice and a blade control element movable in one direction to decrease fuel-flow by means of a device sensitive to the engine speed, and in the opposite direction by means of a device for applying a variable force to the control element in accordance with the desired engine speed, an unobstructed chamber into which both orifices open, and a valve-member for controlling the fuel pressure drop across both throttle valves in series by spilling fuel from the upstream side of the first throttle valve, this valve-member being acted upon by the speed sensitive device and by the pressure of fuel on the downstream side of the second throttle valve in a direction to restrict spillage of fuel, and by the pressure of fuel on the upstream side of the first throttle valve in the opposite direction, the control member and the control element engaging forces of their respective orifices remote from the chamber and the orifices being substantially aligned. The first throttle valve 74 is acted on by a pair of bellows 77, 78 subjected externally to a pressure which can be varied from the full compressor delivery pressure obtaining in a line 81 down to atmospheric pressure by opening vent valves 84, 85 downstream of a restrictor 80, valve 84 being operated by a fan overspeed governor 86 and valve 85 being operated by a temperature sensor 87. The interior of bellows 77 is subjected to the air inlet pressure, while bellows 78 is evacuated. The second throttle valve 75 is operated by the pilot's throttle linkage 105 through a cam 94, a follower 92 and a spring 91, in opposition to an engine driven centrifugal weight 100. A further centrifugal weight 101 acts through a spring upon a rotating valve-member 102 in opposition to the force exerted on the valvemember in the opening direction by the pressure drop across the throttle valves 74, 75 in series. The valve-member 102 controls the by-passing of fuel from the outlet side to the inlet side of the fuel pump 70. A solenoid valve 110 allows flow of fuel from downstream of the throttle valves 74, 75 to starting burners. Stalling of the compressor is prevented by an air-bleed valve (not shown) actuated by a piston unit 111 controlled by a valve 112 which is movable by a diaphragm 116 subjected on opposite sides to the pressure downstream of the throttle valves 74, 75 and the pressure downstream of an orifice-controlled passage 113 connected, via the valve 112, between the outlet and inlet sides of the pump 70. As the engine speed increases, the resultant increase of fuel pressure downstream of the throttle valves 74, 75 increases the opening of the valve 112, producing an increased pressure drop through the passage 113. This pressure drop acts on the piston unit 111 to tend to open the compressor bleed valve. A valve 117 in parallel with the valve 112 is controlled by the temperature sensor 87.