Fuel system planning

[AKKen07]

As I ponder the plan for my fuel system a couple of questions have come up that I haven’t found to be “googleable.” I am planning on using the EFII system which has two return lines through the selector to the tanks. It seems like the fuel lines from the tanks to the boost pump need to be larger to accommodate the total fuel flow, but I don’t see any recommendations for line size. Did anybody else use 3/8” with good results? Also, I assume the return lines would be fine at 1/4”...
My second concern is the fuel selector choice - it seems the Andair valves don’t have a “both” option and the SPRL only come in 1/4” connections. What solutions have you all found here?
As always thank you for any input and ideas!
Ken

Edit: For anybody who is curious: Mr. Paisley at FlyEFII has explained to me that a BOTH setting does not necessarily direct the fuel evenly back to the tanks and could result in an imbalance which is why he recommends the Andair L-R-OFF valve (which sports the AN-6 aka 3/8” fittings). A BOTH valve could be used with a header tank for the return line. As I don’t want to get into that large of a fuel system modification, and don’t like not having the “BOTH” option it seems I have more decisions to make...

[AKKen07]

I guess my Edit didn’t survive so I’ll add to my little monologue this way... Mr. Paisley at FlyEFII has explained to me that a BOTH valve won’t direct return flow correctly to avoid a tank imbalance/overflow situation. Thus the L-R-OFF valve made by Andair is his recommendation. He says A header tank design would alleviate this issue. I don’t know If I want to accept a total fuel system redesign or a non-both valve. More decisions to make...

[AKKen07]

I guess it did survive... anyway more info for anybody in my stage of learning: the Airflow performance FI manual mentioned that 3/8” is standard size tubing for up to 325HP engines. At least on their system.

[Greg_Marlow]

I put in the EFII system too, and have a 6-7 gal header tank in the cargo area. What motor are you using? I have the 360 and 3/8 lines are plenty big. I used 3/8ths for the return lines too.

[AKKen07]

I put in the EFII system too, and have a 6-7 gal header tank in the cargo area. What motor are you using? I have the 360 and 3/8 lines are plenty big. I used 3/8ths for the return lines too.

That is interesting! I am using a 540, but Robert said to use the size you did as well. Did you opt for the header tank rather than the return lines so you could use a valve with Both or do you have other reasons for that? If you happen to have a drawing of your system I would love to see how to plumbed everything.

Thanks for the reply!

[Greg_Marlow]

Yeah, header tank makes it easier. Just an on off valve for the feed line, and a direct return line to the header tank with a one way check valve. I used both of the output fittings from each wing tank that run to the header tank with an on off valve for each tank, that are usually both open, but can be easily closed if I want, for balance, etc. I put an optical sensor near the top of the header tank that gives me a warning should I screw up and leave both wing tank valves closed, or for some reason they aren't feeding the header tank. That gives me 30 minutes or so to fix it, or land.

[AKKen07]

Wow, that’s quite a system! I found some older threads that indicate the potential for a simpler FI system without return lines or extra tanks and I think I’m giving up on the EFII thing. I really liked the idea of that system but I want to simplify a bit... maybe if I didn’t do most of my flying over unfriendly terrain...
thanks again Greg!

[svyolo]

The pumps are positive displacement so at low fuel demand you are returning almost all the fuel to the tanks, if you don't use a header tank. The returns need to be the same size as the feed lines. I am going to use a very small header tank under the right front seat. Less than a gallon. I will return fuel to that. A single vent line goes from that tank up to the mains.

I am using a very small header tank, less than gallon. But I believe if you use EFII's setup Mr. Paisley recommends a minimum of 3 gallons due to fuel heating. SDS's setup, which is mostly similar, doesn't heat the fuel nearly as much.

[Mark Goldberg]

The fuel port size of 1/4" NPT on the SPRL's have proven adequate. Also - the Andair fuel valves have their outlet on the bottom rather than on the side like the SPRL. So it is likely with an Andair you will need a bump on the bottom of your boot cowl because of the outlet and its fittings.

The BOTH position is good to have. I started off with a left/right/off valve on my 4 place, But swapped it out for one with a BOTH position. Flying in the BOTH position, with the way Bob designed the tank outlets, it is hard to fuel starve the engine in a slip or skid. Mark

[AKKen07]

Has the SPRL valve been used much on FI engines with otherwise 3/8 lines? There must be a transition coupling thing...

[jim.mclaughlin924]

1/4 npt is about the same diameter as -6 tube, 1/4npt x -6 male tube is a pretty common fitting.

[svyolo]

I made the same assumption AKKen07 did at first. I thought the 1/4 NPT was necking down the 3/8 fuel line.

[AKKen07]

Live ‘n learn! I haven’t put a bolt on yet and I’ve learned a s*** ton already!