LOW PRESSURE FUEL The low pressure (LP) valve controls the fuel supply from the aircraft tanks to the engine fuel pump. The engine fuel pump includes an LP pump and an HP pump. Fuel from the tanks is initially supplied to the LP pump. From the LP fuel pump fuel is supplied to the Fuel Oil Heat Exchanger (FOHE) for fuel heating and oil cooling. Then the fuel goes through the LP fuel filter.HIGH PRESSURE FUEL The filtered LP fuel is returned to the high-pressure (HP) fuel pump. The HP fuel pump pressurizes the fuel and supplies the Fuel Metering Unit (FMU), the Variable Stator Vane (VSV) actuators and the Air Oil Heat Exchanger (AOHX) modulating valve. The FMU, which contains servo valves, is mounted below the fuel pump assembly. A metering valve in the FMU adjusts the fuel flow delivered to the combustion chamber. This fuel flow, from the FMU, successively goes through the fuel flow transmitter and the HP fuel filter before supplying the fuel manifolds and Fuel Spray Nozzles (FSNs). A Pressure Raising and Shut-Off Valve (PRSOV), installed inside the FMU downstream of the metering valve, starts or stops the fuel flow and keeps the fuel at a satisfactory pressure. An overspeed valve in the FMU can close the PRSOV in case of N1, N2 or LP turbine overspeed.