> The three hose connections of the fuel pump are:
    > 1. Pressurized fuel to the fuel rail and injectors.
    > 2. Return to tank excess fuel via rail fuel regulator.
    > 3. Excess vapor in tank to carbon canister for emissions control.
    >
    > One of the functions of the return line is to eliminate vapor locks.
    > Some newer systems have eliminated the return line by placing the
    > pressure regulator in the tank. Warmed fuel is not returned to
   the tank
    > which would increase vapors. Also, probably saves $$$.
    >
    > I have a good source of fuel Injection info. One of the
   instructors at
    > the Mesa Comm. College Automotive Tech. Dept. (where I take
   classes to
    > keep my brain functional) was a tech the at Phoenix GM Proving
   Grounds
    > for 15 years where he worked exclusively on fuel injection.
    >
    > Joel

   Joel,
   What does your mentor suggest is the best application for Aircraft
   use. I
   would be concerned about accumulated heat with fuel sitting in the fuel
   rail/lines, waiting to be used.
   A question, how does the fuel regulator (in the tank) calibrate pressure
   (fuel) at different power levels.
   I assume the Pressure Regulator at the end of the fuel rail merely
   maintains
   max pressure for a full range of fuel demands and bleeds off the
   excess to
   the tank, to be cooled. This wouldn't seem to me to be the best
   method in a
   non return system.
   George ( down under)

   George,
   In automotive fuel systems, Cost and Emission control are the
   driving forces in design.
   The recirculating system seems the best for aircraft application.
   The regulator maintains a uniform pressure differential between the
   rail and the plenum (intake manifold) because the regulator pressure
   is also controlled by port vacuum.  The resultant is a constant
   pressure differential across the injector.  This means that the
   mixture is only controlled by the pulse width and pressure change is
   not a factor.

   A safety system used in automotive fuel systems is worth considering
   in aircraft.

   1.      When the ignition is turned to run, the fuel pump is
   activated for two seconds which is sufficient to bring the system to
   operating  pressure.  Some fuel would have been returned to the fuel
   tank by the heating and expansion of the fuel during the last engine
   shutdown. V-8’s can rise to 245 degrees F 45 minutes after shutdown.

   2.      The pump relay is activated by a signal from the ignition
   pulse indicating that the engine is either cranking or running.  A
   switch from the oil pressure sender can also be incorporated as a
   secondary source of power to the fuel pump relay.   Either one will
   independently allow the engine to start and run.   An engine
   stoppage will cause both to turn off the pump.

   3.      Ford uses an inertia fuel shut off switch witch will
   disengage the pump in the event of an impact.  I understand that
   Ford has had some problems with their switch.
   Remember, a large amount of fuel can  be pumped into the engine
   compartment in the event of a line failure/crash.

   Joel


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