US Patent 8991186 Fuel control system with servo valve controlled windmill relight mode

A fuel control system comprises a metering valve operable to control the flow of fuel between a supply line and a delivery line, a spill valve operable to control fuel flow within the supply line, a pressure raising valve connected to the delivery line, and a control servo valve movable between a thrust control mode in which it modifies the control of the spill valve to reduce the fuel flow delivered via the metering valve and an outlet of the pressure raising valve, and a windmill relight position in which it modifies the control of the pressure raising valve to allow fuel delivery through the outlet of the pressure raising valve at a reduced system pressure.