EFI fuel supply system

[GEM930]

I'm installing an electronic ignition/electronic fuel injection system on my 0320 H2AD and had a question I was hoping the group could help me with. The supplier of the system (Tracy Crook at Real World solutions) recommends drawing from and returning to the same tank and using a transfer pump to move fuel from the other tank. I have opted to do this to simplify installation and cost (duplex valves are EXPENSIVE!!!). I installed 2 bulkhead fittings in my left tank (one for return and one for transfer) The facet pump will act as a one way valve (keeping fuel from the left tank from flowing to the right), but will allow fuel to flow from the right to the left tanks when the pump is off. My question is --- is there a problem with this? I can't really think of a situation where this will be a bad thing. If the plane sits a while with more fuel in the right tank, the tanks will equalize, but this does not seem to be a bad thing. Can anyone think of a reason why I would not want to do this? I could put an electric valve (primer) in the system, but I'm not sure it is necessary. Just for info, I plan to leave the original valve in the system. In case of pump failure I can always suck off the right tank and return to the left and then switch back. It will also leave me a way to completely shut off the fuel in case of an emergency landing. Any info will be greatly appreciated.

GEM

[TSwezey]

I would do what ever Tracy has on his. He knows his stuff very well. Send him an email or call him. He will answer any questions you have. Just make sure you know their vacation schedule. They are usually away when you have the biggest problems. My engine controller was built by him.

[GEM930]

Tracy uses a header tank, which is just not an option for me, due to space.

[N941WR]

Yes duplex valves are expensive but they are a very simple solution compaired to adding a transfer pump.

Simple is best when dealing with your fuel system.

[John Clark]

Way too complex with too many possible points of failure. Go with the duplex valve.

John Clark
RV8 N18U "Sunshine"
KSBA

[nucleus]

Originally Posted by N941WR

Yes duplex valves are expensive but they are a very simple solution compaired to adding a transfer pump.

Simple is best when dealing with your fuel system.

I would prefer the duplex valve solution as well, but it does mean adding another pump and return on the other wing, so it is hard to call it simpler. Remember this is EFI, so no mechanical engine pump.

I like the idea of having two pumps available... You are running a boost pump as well?

The system you have planned should work fine.

The biggest problem I see with transfer pumps is the scenario where it is ON when it should NOT be, and you pump fuel out your fuel vent. This is a pretty common problem by the way, airliners have done it.

If it were my plane I would have in tank pumps in each wing and a boost pump on the common line, but your system will work fine too.

Is Tracy flying his RV-8 yet? They haven't updated the website in an age.

Hans

[Bob Brown]

I've been flying a fuel injected system with a purge valve for three years. I rarely use the purge valve, it is plumbed to pump from the right tank and return to the left tank. The purge valve is the only moving part in this setup...I don't understand the need to add more complexity (additional pumps) or cost (duplex valve) just to put the fuel back into the same tank it was pumped from. Should my system not be working as well as it seems to be?

[GEM930]

The system is an electronic system much like what is in a modern car. It continually returns fuel to the main (left) tank. If you tried to draw from the right tank you would quickly drain it and fill the left (perhaps to the point of dumping fuel out the vent. I agree a duplex would be the simple solution and if I were building from scratch I would go that route, but this is a retro. A duplex would require a mess of plumbing I'm just not willing to do now. My a&p pointed out the "con" of the increased complexity, but he also pointed out the "pro" of being able to move all the usable fuel to the main tank when both tanks are low. I already have a timing circuit that will keep me from pumping fuel overboard and I will leave the valve in place in case the pump or circuit fails. It just does not seem that complex to me. For good or bad I have ruled out the duplex at this time.... So back to the original question... Do I need to worry about fuel equalizing from the right to left tank? I can't think of a situation when this wouldl be bad... Can anyone think of one? Fuel will not move from the main to the aux and fuel could not be pushed out the vent as the tanks would equelize before that could happen. Sorry for any typos... Writing this on my iPhone.

[frankh]

Fuel equalising is a bad thing. the head difference of one tank being slightly higher than the other means the flowrate will be pretty low. Now of course you could add an Andair check valve (vans) or put a facet pump in there with the check built in.

certainly a Facet (even with an external check) is way cheaper than a duplex return valve.

frank

Inventer of the wingroot electric pump system.

[McFly]

I am certainly not claiming to be an expert, but I cannot think of a reason why the tank equalizing in a failure/off mode would be a bad thing as long as you still have access to all fuel. Hopefully others will chime in. Good luck.