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


 After a while with out the HP pumps going
 the facets would pump fuel up through
 the vents in system 2. Why I like Pauls drawing 3.
 Simpler too. Non return valves after the facet and
 the float valve, I would say in the surge tank, will be
 necessary to allow room for returning fuel. And
 stop one facet from losing fuel flow into the
 opposite tank.

 Not sure what facet pumps you are using, but the
 facet pumps used in earlier Mazda vehicles were
 only good enough to supply a standard 12a or 13b.
 Any mods to those engines and they would prove
 to be inadequate. Why I liked the Holley LP pumps,
 they had much better flow volumes. A Holley blue
 would easily supply my old 12aT at 250hp up
 to 305hp.

 Sam


There still remains the problem I mentioned in my earlier
email with fuel system 3 pertaining to rotary type low
pressure fuel pumps as opposed to the diaphragm types.
When that float valve is closed, probably at idle where
fuel demand from the engine is very little, there is no
pressure relief for the facet pump that is working.
Rotary style pumps must have a return, as Mazda
provided for their carburettored vehicles.
(they didn't do this for fun ;o) Without a return they will
 be " pumping against a brickwall ".  Prolonged periods
of idle as in rush hour (air)traffic, something you American
city fella's see a bit more than us out here in NZ, will
cause the rotary type pump to overheat because it is
operating under much more back pressure than it was
designed for.


For this reason I suggest a revised solution as in my diagram.
It looks to be a combo of both Paul and Pierre's system.
Whichever low pressure pump is operating so must the opposite
SSOV. This will return surplus fuel to the tank in use. But I reckon
you knew that already Pierre. Use an overflow from near the top
of the surge tank to return fuel to the top of the main tanks.

If the high pressure pumps are both operating simultaneously
as I think was stated earlier, there are no issues that I can see,
unless one fails. If they operate separately, just like one has failed,
they must resist backflow pressure higher than the pressure relief
valve setting to maintain redundancy. If they don't resist that much
back pressure, add one way valves after each HP pump

Sam

The Facit pumps are not rotary Sam. They were used for 40 years
with carbs with no return lines. They have been around for ever.

They were designed for carbs with float valves.

MAX-MIN SHUTOFF PRESSURE 5-3.5 PSI
15 GPH, negative lead .25",1/8-27 Interior threads, positive shutoff valve.
Solid State Reliability Pumping 30 G.P.H. @ 2 TO 4 PSI.
Use with Gas or Alcohol.

You don't need the return pumps.

Paul Lamar