GB1492384A - Fuel control systems for gas turbine engines - Google Patents

Abstract

1492384 Gas turbine engine fuel systems LUCAS INDUSTRIES Ltd 20 March 1975 [15 May 1974] 21673/74 Heading F1G A gas turbine engine fuel system comprises an engine-driven fixed displacement fuel pump 11 followed by a metering device 12, a spill valve 15 for spilling fuel from the outlet to the inlet of the pump and responsive to an increase in the pressure intermediate restrictors 13, 14 which form a fluid potentiometer across the pump to increase the spill flow and responsive to an increase in the pressure downstream of the metering device to reduce the spill flow, and means 20 biasing the spill valve to reduce the spill flow. The ratio of the effective areas of a piston 16 subject to the intermediate pressure and a piston 17 subject to the downstream pressure is the increase of the ratio of the pump delivery pressure and the intermediate pressure, whereby the forces acting on the pistons 16, 17 are substantially in balance and the spring 20 is required to exert little force. The restrictions 13, 14 have a damping effect on movement of the spill valve 15. The metering device 12 comprises a variable metering orifice responsive to the engine speed N, the compressor intake and delivery pressures P 1 and P4 and the setting # of a power demand control, and a regulator valve downstream of the metering orifice and responsive to the pressure drop across the metering orifice and the engine speed N to maintain the pressure drop substantially constant for a given engine speed.