601 HDS Fuel System Question

I had a question regarding my 601 HDS airplane's fuel system.  I bought this airplane a couple of years ago already built.  It's a 1999 build that evidently just had the header tank originally and then LE wing tanks were added later.  Right now the way it's set up, the wing tanks pump fuel into the header tank and the header feeds the (Rotax 912 ULS) engine.  I have a problem though sometimes if I get distracted - even with a countdown timer stuck right in front of my face on the instrument panel - and forget to turn off the wing wing tank pump.  Then the fuel overflows from the header tank cap and into the cockpit which is not a good situation, obviously.  (At that point, my 'reminder' is that I smell fuel so I shut off the fuel pump but by then I'm at considerable risk for a fire.)  It's an accident waiting to happen.  I have a halon fire extinguisher installed in the cabin but that's small consolation for this situation.
To resolve this, I was thinking of routing the wing tank lines to a 4 way fuel valve (already installed) instead of to the header tank so that the wing tanks would feed the engine directly.  As I envision it, the fuel valve selector switch would allow me to point to either the header or the wing tanks as a fuel source.  Do you see any issues with doing that?  I ask partly because the wing tank fuel pumps are located on the cabin floor; would I need to relocate them closer to the wing tanks?  Or would I even need them at all if I route the wing tank lines directly to the engine where the electric and mechanical fuel pumps are already located in the engine compartment?  I've heard it's better to 'push fuel' rather than 'pull' it - or would that matter in this case?
Any thoughts, ideas, or other solutions that you may have on this matter are greatly appreciated. 

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Permalink Reply by Chris Beebe on October 10, 2018 at 7:34pm

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.

Permalink Reply by Rolf Grandstaff on October 17, 2018 at 6:26am

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.  

Permalink Reply by Bob Pustell on October 16, 2018 at 5:36pm

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.

Decisions, decisions.............

Permalink Reply by Bob Pustell on October 16, 2018 at 6:02pm

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.

Permalink Reply by Rolf Grandstaff on October 17, 2018 at 6:27am

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.

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