Pressurizing valve Start fuel enrichment solenoid Fuel outlet (to fuel oil  cooler) Fuel shutoff valve Torque engine Metering head  sensor Evacuated bellows Servo pressure regulator Servo metering valve assembly Fuel bypass  valve Manual mode  cam Idle set stop Manual mode solenoid (shown auto mode) Speed set Overspeed stop P3 Inlet Vane fuel pump Fuel return Fuel inlet Mechanical speed governor P3 Air Pressure fuel Return/bypass fuel Figure 2-49.  Fuel control assembly schematic hydomechanical/electronic.  Figure 2-50.  Fuel pump and filter. 2-36 3. The hydromechanical fuel control assembly provides  the fuel metering function of the EFCU.  pressure condition before bypassing occurs, by  extending a pin from the fuel filter bowl. Fuel pump  discharge flow in excess of that required by the fuel  control assembly is returned from the control to the  pump interstage. Fuel is supplied to the fuel control through a  200-micron inlet filter screen and is metered to the  engine by the servo-operated metering valve. It is  a fuel flow/compressor discharge pressure (Wf/ P3) ratio device that positions the metering valve in  response to engine compressor discharge pressure  (P3). Fuel pressure differential across the servo  valve is maintained by the servo-operated bypass  valve in response to commands from the EFCU.  [Figure 2-49]  The manual mode solenoid valve is  energized in the automatic mode. The automatic mode  restricts operation of the mechanical speed governor.  It is restricted to a single overspeed governor setting  above the speed range controlled electronically.  Deenergizing the manual mode valve enables the  mechanical speed governor to function as an all speed  governor in response to power lever angle (PLA). The  fuel control system includes a low power sensitive  torque motor which may be activated to increase or  decrease fuel flow in the automatic mode (EFCU  mode). The torque motor provides an interface to an  electronic control unit that senses various engine and  ambient parameters and activates the torque motor  to meter fuel flow accordingly. This torque motor  provides electromechanical conversion of an electrical 