Thanks everybody for their input. This is why I love the Rotary Forum.
There
are so many different guys with a wide variety of expertise, that there
will
always be someone with firsthand practical experience to give their
opinion.
Because I don't fly that often, I tend to think what works well for a car
will automaticaly work on an aircraft.

Attached is try nr two. I want to have a system that is simple,
inexpensive
and requires minimum input from the pilot.

This is essentially an electrical controlled system (In my trade). I'm
thinking of having a centre console mounted rotary switch with left, right
and off positions. In the left and right positions it will switch on the
relevant Facet pump and open the relevant return line solenoid. A
mechanical
overide will be incorporated to prevent me from switching it Off by
accident. My thinking on the centre solenoid, forward of the HP pumps, is
to
have it open for both left and right positions but closed in the Off
position. This is to cut off all fuel in case of an engine fire.

The left and right HP pumps will be controlled by two switches on the
panel
so that either one or both can be switched on as required.

I'm planning to build an electronic timer to give me a visual
indication,flashing LED, of approx. 20 minutes to remind me to switch
between tanks.

I have a few qustions though:

1. Will the HP pump ensure that the facet pump does not pump fuel
overboard
through the vents. I'm thinking to maybe wire it up in such a way that the
Hp pump is switched on before the Facet pump goes on. Or would I need a
mechanical way, needle and seat or float valve to control it?

2. Can I use car airconditioning solenoids for the fuel?

3. Are there any restrictions on the size of the surge tank? Can I use it
to
increase fuel tank capacity?

4. Are the fuel supply and return lines the right size?

Pierre


I think you should return all fuel to the sump tank. No return solenoids
required.
A float valve is a good idea. The facet pumps are used to feed carbs with
float valves. T the Facet pumps together before feeding the sump. Check
them
for one way valves. If they don't have them get some.

Here is your 2nd drawing modified to my suggestions.

Questions:

2. I don't know.

3. Other than weight and balance no. Yes it can be used to increase fuel
    capacity.

4. 3/8th are fine for everything. Vents can be 1/4 inch.

A sight gage on the sump tank is a good idea if it is mounted high.

Paul Lamar

Thanks again. I'll use your system. I might just replace the remaining
solenoid cut-off valve with a manual ball valve. Less to go wrong.

Pierre

A good float valve is essential as 5 psi fuel pressure can blow up
a large sump tank. Another trick is use a pressure switch in the
sump tank to turn the facet pumps off when the tank is full.
Just make sure there is an over ride switch in case the pressure
switch works.

Paul Lamar

Paul
the facet pumps are used to supply carbies
with a float valve as you say, but they also have
a return line provided by Mazda to dump off
excess fuel and pressure when the bowls are full.

Simplest way to stop the low pressure pump
rupturing a large surge tank with hydraulic pressure
is to provide a return line to a vented main tank.
I'm sure fuel system 4 I have just sent you will
cover the bases well. No pressure shut off for the
LP pump, and no float valve. Also sure the earlier facet
pumps wont cut the mustard.
Sam

Tracy Crook and others have been flying with the Facit pumps
for years and hundreds of hours. Tracy uses just one wing tank
to return fuel too and a Facit pump to transfer fuel from
the other tank to the main tank.

If you forget to transfer fuel the engine could stop at a
inappropriate moment :)

Fuel management pilot error is one of the major statistical causes of crashes.

I always slip whenever possible so I am always high enough
on approach to make the runway regardless if the engine stops or not.
None of this dragging it in for me. That also makes it easier
to land on the numbers.

Paul Lamar