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Date: Mon, 11 Jun 2007 17:58:26 -0400
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Subject: Re: Boost switch
From: "bob mackey" <n103md@yahoo.com>
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> What failure modes exist where fuel pressure may drop but adding more
> fuel will make the problem worse (i.e. the boost pump coming on
> automatically)?

A broken fuel line would be somewhat worse with the boost pump
automatically activated.

> Is there something that can be done to the normally aspirated
> continental IO-550 that no matter how many pumps are driving
> fuel to the engine, the mixture control is still very much in charge?

In order to make the mixture knob the solitary control of
fuel/air ratio, the sensitivity to fuel pressure must be
eliminated. That could be done by regulating the fuel pressure
just upstream of the injector servo. As some have noted, making
such a change offers new opportunities to make tragic errors.
One area of concern would be what to do with the excess fuel
at the regulator? Return it to the same tank? Or always return
to the tank it came from?

On the other hand, pressure regulation might solve the pilot
interface problem of having multiple interacting mixture controls
(mixture + boost pumps).

-bob