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On my 601 with a rotax 912 I have two wing tanks. One mechanical fuel pump and two electric pumps in the cabin. I only use the electric pumps for emergency or fuel priming. Then I use a fuel selector to run whatever tank I want to pull the fuel from. This setup works well and I don't have any issues with it. I also moniter fuel psi with my engine management system.
That sounds good, Chris. I think I'll proceed with a mod to the 4 way fuel valve so that it's pointing to each of the 3 tanks - header, left wing, right wing - and use the existing electric pumps in their current locations to prime. Thanks for the info. I've spoken with several builders and A&Ps and most seem to think this should work fine. We'll see.
I like your thought of pulling the fuel with electric (or engine driven) fuel pumps ahead of the firewall. Pushing fuel gives you fuel under pressure inside the cockpit. It there is a leak in the plumbing when pushing fuel, the fuel spew out the leak into the cabin. If you have a leak in plumbing while pulling fuel you will pull air into the leak and the air bubbles flow along with the fuel to the engine area. Fuel under pressure in the cockpit is to be avoided, in my opinion.
Your other option would be to install a float switch in the header thank that shuts off the transfer pump when the header tank is almost full and then turns it on again when the fuel level drops. This would prevent your overflow problem but leave you with fuel under pressure in the cockpit when the transfer pump is operating.
After sending my reply I realized that another option would be to eliminate the header tank and just use the wing tanks pulling fuel with pumps ahead of the firewall. That would eliminate your problems and also eliminate the risks associated with having a fuel container sloshing around above your knees. In the event of a crash with header tank rupture you have a real problem. Add an ignition source during that crash and you have a major problem.
Finally, I would suggest you check out your fuel system as currently installed. I think having fuel tank overflow end up inside the cockpit is a terrible situation -- there should be some kind of overboard vent, in my opinion. If the plane is not set up that way currently it should be modified to prevent fuel in the cockpit as a "normal" thing.
Thanks for your reply, Bob. Yah, the current situation where the header tank can overflow is definitely asking for trouble so I need to make a change. You'd be surprised how many of these older 601s are evidently set up this way. I'd like to keep the header at least for now but NOT route the wing tank lines into it. I'll give the wing tanks their own position on the fuel selector valve and use that to route each of the wing tanks directly to the carbs/engine.