Dan,
My understanding (from reading the Columbia 400 manual) is
that the Low mode is used for vapor suppression above 10,000 ft.
The High is used when the
mechanical pump fails, during prime, and prior to a hot start to cool any heat
soaked components in the fuel system (as the hot excess fuel is returned to
your fuel tank).
When you setup your fuel system for
your engine you should verify that high fuel pump mode will not flood your
engine.
In the Columbia (as I understand) the prime button
engages the high fuel mode.
They have a three way switch, LOW,
OFF, and HIGH arm.
The HIGH arm uses a fuel pressure
switch and locking relay. The intent is if the fuel pressure drops while on
HIGH arm, the HIGH mode of the fuel pump is engaged and is locked in, even as
the fuel pressure rises as a result of the pump coming on.
The HIGH arm is used during
climb and cruise below 10,000 ft and set to OFF during descent. (And of course
the LOW is used always above 10,000 ft).
I assume you would go to HIGH
arm on a go-around … one more thing to the checklist during a busy time.
It’s important to make
sure that HIGH and LOW are not engaged at the same time. So there is some care
to how the primer button interacts with the three way switch.
This is how I am setting up my
IV-P.
r.t.s.
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf
Of Dan Reagan
Sent: Thursday, June 18, 2009 8:09
AM
To: lml@lancaironline.net
Subject: [LML] Boost pump question
Since my crankshaft bolt problem is causing me to change out
my engine, I have decided to change from my current FADEC engine to a
conventional mixture control engine. The boost pump I currently have is a
2 speed Dukes and in the past was turned on and off by FADEC. (It could be
manually turned on as when above 10,000 feet)
My question is, when I am rewiring the fuel pump, do I need
both the high and the low speeds? My dumb question of the day
is, when is the fuel pump supposed to be used on the TSIO550 in the
Lancair IVP?