Charlie,

I transferred fuel to a T in the return line from the regulator.  The regulator return was connected to the side branch of the T.  I suspect that the back pressure from this connection adversely affected the flow rate from the Facet pump.  A separate line to the main tank or a different connection arrangement at the T might have been better.  The high pressure pump had a higher and predictable flow rate.

While returning the fuel to only the main tank would work, it seems to leave the possibility for a couple of undesirable situations.

One would be in the event that the supply from the main tank were compromised, fuel would have to be drawn from the aux tank while the returned fuel would accumulate in the main tank where it would be inaccessible and possibly vented.

A second possibility would be to draw fuel from the aux tank and return it to an operational but full main tank where it would be vented.  I’m sure you would not do this.  Me?... I’m not so sure.

Steve

Ouch; I hadn't thought about that. But I suspect that even a low pressure pump would damage the tank if the vent is blocked. Thanks for the data point on the fact that a high pressure pump can be used effectively as a transfer pump.

Were you using a separate port on the main tank for your transfer point? My tentative plan is to T into either the regulator return, or (assuming an effective back/anti-siphon setup), into the main supply between tank & engine pump. Obviously, the anti-siphon feature would need to be bullet proof to tap the supply line.

One option I've considered is to use the fuel selector 'normally', but have all regulator bypass return to a single 'main' tank. This arrangement is actually used in some certified planes with injected Continentals, but I'm leery of having my primary engine pump run dry for even a very short interval as I empty an aux tank. I suppose that with that arrangement, it would only run dry for a couple of seconds ( :-> ), so maybe it would work out fine. Any thoughts?



Charlie