The VW mechanical fuel pump will not pass fuel when the engine is not running. On the Beetle car this is a crash safety feature to serve as an automatic fuel shut off. On my airplane I put one check valve in parallel with the mechanical pump and a 3.5 psi Facet electric pump in series close to the outlet of the fuel selector valve. The fuel selector valve allows selecting either wing tank and will shut off both tanks. Fuel will free-flow through the electric pump. To prime the system and for take off and landing, the electric pump insures fuel supply. During cruise and ground operation the mechanical pump does the job without using any electrical power. This fuel setup is simple, uses the minimum components and provides the needed redundancy for me.
Ground testing per the FAA requirements for excess fuel flow capacity results are: 21 gallons per hour for the VW mechanical pump, and 23 gallons per hour for the Facet electric pump all at worse case conditions of minimum fuel and maximum angle of attack. At WOT my 2180 VW uses 3.6 gallons per hour. Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA > ------------------------------ > > From: Douglas Cooke <dbcrn at hotmail.com> > > Maybe I'm missing something, but why not a mechanical pump with a parallel > bypass containing a one way valve the electric pump located upstream from > both the > mechanical pump and valve? > That way the electric just bypasses the mechanical pump and the mechanical > pump > won't pump back to the tank(s). > > "I did a little checking and you can't push fuel through the VW mechanical > pump > so a backup system would entail, at minimum, a couple check valves and > an electric pump...a bit more complicated that I care to make it." > > ------------------------------ >
