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Date: Thu, 21 Sep 2006 20:37:47 -0400
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Subject: Re: [LML] Boost pump switching
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From: "John Schroeder" <jschroeder@perigee.net>
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Alan -

We wired our boost pump (Dukes 2 speed) for our ES IO-55N2 with a switch we got from B&C (S700-2-10). Down is off, mid position is low boost and full up is high boost. There is no momentary action for any of the positions. Am sending you directly a .pdf file that shows the wiring and also the annunciator circuitry.

Whether low boost can handler the failure of the engine-driven pump depends on engine power levels. High puts out about 1.3 gallons per minute (78 gph) and that is a lot of gas. We measured it the fuel metering valve on the engine (the one that outputs to the spider). It will most probably kill the engine. I can't recall the flow rate we measured on the low boost, but it was in the high 30's gpH, as I recall. I'd rely on low boost in this instance and goose it to high for a few seconds if it started to die.

Hope this helps.

John


On Thu, 21 Sep 2006 18:38:20 -0400, Alan K. Adamson <aadamson@highrf.com> wrote:

> So.... (don't ya just love it when an email starts this way :) )
>
> I've seen most IO-550's with 2 boost pump switches.  I'll assume they are
> used as follows.
>
> Low Boost - switched on at or above 10K feet and run for the duration of the
> flight at that level to provide added purging of vapors or bubbles that
> might exist in the lines
>
> High Boost - Prime at startup.
>
> Ok, now, I've also heard that you use High Boost any time you loose an
> engine driven fuel pump.  Will low boost suffice?
>
> Here's the reason I ask.  I designed my panel for 1 fuel boost switch and
> was going to use an ON-ON-(ON) type switch.  This would allow switching to
> low boost at 10K and using momentary high boost for prime/startup.  But it
> wouldn't allow using High boost in an engine fuel pump failure scenario, but
> low boost would be available.  This is no a turbo installation btw.
>
> I've found a couple of switches that I could replace the single with that
> will allow switching to low and locking out high unless placed there, or I
> could go to an ON-ON-ON type without the momentary.
>
> So, could you splain to me, what the various boost modes are or if there is
> another compromise that I haven't thought of with one switch.
>
> Thanks in advance,
> Alan
>
>
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