Hi Jeff,
Another option would be to put a one way valve in the output of the
engine driven pump. T the two lines together after the valve. I think
some of the electric pumps provide a one way flow, but if not, you
would need one there also to prevent the mechanical pump from bypassing
the engine. I seem to recall a Faucet pump I had would flow backwards
sometimes depending on where it stopped when it was turned off.
Bob W.
On Mon, 16 Nov 2009 12:09:41 -0500
"Jeff Page" <jpx@qenesis.com> wrote:
>
> I just came across a notation I made quite a while ago, after noticing
> a neat idea, probably on this list.
>
> It utilizes a low pressure switch to provide an "automatic" mode to
> the electric fuel boost pump, so that if the engine driven pump
> failed, the electric one would be powered up.
>
> This seemed like a great idea at the time. It would likely mean an
> engine hiccup, followed by the fuel pump on LED illuminating - much
> better than the pilot conjecturing the engine failure is due to fuel
> starvation and manually turning on the pump (would be a checklist item).
>
> However, looking at the schematic as I drew it, as soon as the
> electric pump provided sufficient pressure, the low pressure switch
> would open and the pump would shut off, and then back on, and then
> off. Ooops :-(
>
> Is it worth fabricating a little latching circuit to provide this
> automatic operation, or better to keep things simple ?
>
> I don't do hard IFR, and manually turning on the fuel pump switch in
> most circumstances would be sufficient to avoid an unpleasant landing.
>
> Thoughts ?
>
> Jeff Page
> Dream Aircraft Tundra #10
>
>
>
>
>
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