Please find below how the fuel flow in RB211 Trent 700 fuel circuit following the schematic attached to this study.
Note: The schematic photo is taken from AIRBUS CBT CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.
The fuel system is used to receive fuel from the tanks and deliver conditioned metered fuel to combustion chamber. Also some fuel is sent to as a muscle pressure for the AOHE - Air / Oil Heat Exchanger - modulating valve and the VSV - Variable Stator Vanes - actuator system.
THE FUEL CIRCUIT:The fuel enters the engine through the LP fuel valve in the pylon. It enters the LP stage of the fuel pump and then delivered to the FOHE - Fuel / Oil Heat Exchanger - to cool the engine oil and warm up the fuel. Then the fuel passes through LP filter and then it is delivered to the HP pump.
For the fuel LP filter, there is a bypass that will open in case the fuel filter is clogged.
Some of the HP fuel is delivered to the AOHE – Air Oil Heat Exchanger Valve – and the VSV – Variable Stator Vanes. Another part delivered to the FMU - Fuel Metering Unit-.
Inside the FMU, there is a PRESSURE DROP AND SPILL VALVE that will open in case of high unwanted fuel flow through the FMV. Then the fuel flow and pressure is controlled through the MV – Metering Valve – and the PRSOV - Pressure Raising and Shut Off Valve-.
The EEC - Electronic Engine Controller - controls the FMV to open or close by TM - torque motor -. This MV - Metering Valve - position fed back the EEC regarding its position through resolvers.
After the fuel metered through the FMV, it passes through the PRSOV and then supplied to 24 fuel nozzles after being filtered in the HP filter.
When the PRSOV is closed after engine shut down, there is a mechanically connected DUMP VALVE that will open allowing fuel remained in the manifold to be drained into drain collector tank. This unburned fuel will be sucked at next engine start by the LP pump.
The PRSOV is controlled independently from the EEC by the Master Switch. This will operate the torque motor to close the PRSOV whatever the EEC demand signal is.
In the FMU, there is an OPU – Over speed unit – that will close the PRSOV independently from the EEC if the EEC failure occurs.
Differential pressure switch installed through the LP filter signals the EEC in case of differential pressure is more than 5 PSI.
Fuel flow transmitter signals the EEC regarding the fuel quantity passed through it.
The FF - Fuel Flow - parameter is indicated on the ECAM SD - System Display - ENG PAGE AND CRUISE PAGE. Downstream the LP fuel filter there is fuel LP switch that give signal when fuel pressure less than 70 PSI. It indicates either low fuel pressure or the engine will shut down. As a result the failure will be transmitted to the CMC - centralized Maintenance Computer -.
Two fuel temp thermo couple are as the engine oil sensor signals the EEC as priority control for the heat management system (AOHE) control.
Two Microswitches are used to indicate PRSOV is closed during engine shut down or during turbine over speed test.
This was a short briefing about the fuel circuit in the Trent 700.
B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer
