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