EFI Aux Tank Plumbing

[RonJones]

I'm toying with the idea of converting my BC Broncos early 24 gal tank to the Holley Atomic 2 EFI when it comes available. I'd also like to keep my Aux Tank functional without running fuel and return lines everywhere and switching to a 6 port electric fuel valve. The 6-port EFV's I've seen are rated to 60 psi (maybe), but plumbing schematics show them placed to switch before an inline pump.

Holley sells a inline regulator/filter to mount close to the main tank, so only a short return line is used.

I'm thinking place a low-pressure inline electric fuel pump on the Aux tank outlet and Tee it into the Holley inline regulator/filter return line (see below). The fuel pump would be powered by the Main/Aux selector switch. When the Aux Tank fuel level nears zero, switch back to the Main Tank, which should now be several gallons fuller. This way a short return line is used and no 6-port EFV is needed. If the Aux fuel pump doesn't have a check valve, one can be added.

Any thoughts?

 

[RonJones]

Here's a check-valved 15 gph pump that runs at 1- 2 psi, a little over a half hour to transfer an Aux Tank, and at low enough psi not to mess with a return line, I think:

 

[Steve83]

Bad idea. Your design does not allow safe operation under all possible conditions.

What if the aux pump is activated when the main tank is full? What if the aux pump is activated when the aux tank is empty? Most high-pressure electric fuel pumps can't tolerate running for more than a few seconds when dry. And a low-pressure pump rated for 2psi probably can't tolerate 30~100 psi at its outlet.

A better way is to first plumb an overflow line (capable of passing MORE fuel at ~0psi than the pump's max) from the main tank's filler neck back to the aux tank. Then wire an independent transfer pump circuit to a low-pressure pump that WILL tolerate running dry. But add a low pressure switch (like the '87-up 6psi oil pressure switch) to the transfer pump outlet that will activate a warning light (or cancel the pump relay) when there's no pressure (tank empty - nothing left to transfer).

 

[RonJones]

What if the aux pump is activated when the main tank is full?

I fly an aircraft that has the same kind of FAA-certified transfer system; it's not that hard to remember to burn enough fuel to allow room for the Aux fuel. In fact, the Facet fuel pump referenced above is the same kind used in the FAA-approved version. They are air-tolerant.

I had no idea that return fuel is up to 100 psi; if that's so, then how about plumbing the Aux Tank outlet so that it Tee's into the Main Tank outlet before the accumulator and any low pressure pump? Excess fuel is pumped into the main tank, and air bubbles should be handled by the accumulator, but a low pressure fuel switch could shut off the transfer:

https://nitrousoutlet.com/i-30559956-fuel-pressure-safety-switch-and-6-an-manifold-low-pressure.html

A warning annunciator would be nice; a tone would be even better!

 

[AZ73]

I ran a low pressure pump from the rear tank to a GM (Pollack) 6 port. After the port I ran the high pressure pump. My aux tank gravity feeds to the port and since it's higher than the port and the high pressure pump, the high pressure pump pulls from it.

This is the port I used http://products.pollakaftermarket.c...-valves/light-truck-6-port-motor-driven-valve

I followed this schematic

https://forum.ih8mud.com/threads/resolved-help-pollak-6-port-problem.826000/

Since you're running a return line from carb anyway all the way back to the rear tank, you can just put the port in the middle of the lines, and run 2 short lines to your aux tank,

 

[RonJones]

In the Atomic System, the inline high pressure fuel pump is within 2 feet of the main tank, so with the filter/regulator above, there's not a lot of return line, either.

I like the Pollack valve. as it's rated to 65 psi, and seems to manage that just fine, from reviews. A lot of the 6 way valves seem to be rated only to low pressure. How did you send the Aux Return line to the Aux Tank? I only think I have filler, filler neck vent, vent, and outflow.

 

[Broncobowsher]

Run a high pressure pump from each tank. Nearly every HP pump has a check valve built in, if not one can be added.
T the outlets of both pumps together and send that through a final filter to the EFI
Return can be 2 different ways. Either simple and everything goes to the main.
Or slightly complex and a simple solenoid style fuel tank selector valve. The return is under no pressure to speak of, don't need a high pressure valve for the return.
If you wire the selector solenoid to the aux tank pump, when you switch tanks, pumps change, and the return path changes.

You could also do boondock fixes. By manually powering/de-powering the solenoid you can make a transfer pump into the other tank. You can swap lines and move one pump to the other tank. Stuff like that.

It is super simple. Minimal number of connections, parts used, etc. About as redundant as possible without just carrying spare parts in the tool box.

 

[RonJones]

That makes sense having a backup pump! I might go with the simple singler return line.