GB1342733A - - Google Patents

Abstract

1342733 Gas turbine engine fuel systems DEFENCE SECRETARY OF STATE FOR 19 April 1971 [13 April 1970] 17509/70 Heading F1G An engine fuel system comprises an enginedriven fuel pump 5, a restrictor 6 and a fuel metering device 7 in series; a governor 12 having a diaphragm 14 responsive, via passages 22, 23, to the pressure drop across the restrictor 6 and metering device 7; means responsive to the position of the diaphragm for controlling the fuel flow passing to the downstream end of the main fuel duct; and a spill duct 30, 31, 32 communicating with the main fuel duct at a point between the restrictor 6 and the metering device 7, a valve 33 being provided for varying the spill flow in accordance with variations in the fuel density. A diaphragm 54 is open on its underside to the compressor intake pressure P 1 and is subjected on its upperside to a pressure derived from an air potentiometer 45, 46 connected between the compressor delivery pressure P 2 and the intake pressure P 1 , this derived pressure being modified by a bleed to atmospheric pressure, or a pressure related thereto, via a vent 49 controlled by a valve rod 50 which is acted on by the pressure differential existing across the diaphragm 14 and the opposing force exerted by a spring 26, the spring force being controlled by the pilots throttle lever 28. The diaphragm 54 acts on a lever arm 60 in conjunction with an evacuated bellows 58 subjected to the absolute value of the pressure P 1 . The other arm 61 of the lever carries a half-ball valve 64 which controls the bleed of fuel through a restrictor 68 and thereby controls the pressure differential acting on the fuel metering valve 66. The valve 66 is connected to the lever arm 61 by a spring 65. During normal running, the governing pressure controlling the metering valve 66 is varied by the valve rod 50, so as to maintain the engine speed substatially at a selected valve but during acceleration the rod 50 closes the vent 49 and the governing pressure is then dependent only on the pressures P 1 and P 2 . During deceleration, the vent 49 is wide open, and the governing pressure then varies only with the pressures P 1 and P 2 . Compensation for the effect of variation in fuel density is effected by the spill valve 33, which is acted on by governor flyweights 43 which are submerged in fuel and therefore subjected to a buoyancy effect which increases as the fuel density increases. Instead of controlling the pressure applied to the diaphragm 54, the governor 12 may control a spill flow from the passage 25 or the passage 74 to the inlet side of the pump 5.