"BOTH" fuel selector without interconnecting L and R tanks

[Gilbert Pierce]

My most often flown trip is So Cal to Phoenix. 8-10 hour drive, It is often a 3 hour trip. With my 160HP O-320, 9.6 to 10 GPH at 2500 RPM, I usually make it with VFR reserves, (6-8 gal) depending on the wind. I know because I have a fuel tank dip stick I trust, and my gages agree. If I thought my tank was topped off and "it was not" because I fitted my plane with a new STCd fuel selector with a Both/ Off as a choice, I could easily end up with less fuel than planed, unless I went back to the first tank filled, and re checked it was still topped off after filling the second tank.

I agree this is not an issue for short hops, unless you have a fuel computer. You could easily over estimate the fuel on board, filling tanks with the selector in Off or Both. Hope I am not beating a dead horse. The above situation is exactly what we face with my Fathers C-182

Steve M.

Iam with you 100% for exactly the reason you quoted. Most of flights are long.

[PACERGUY]

Steve, Brian
I always questioned why the Cub Crafters system had the crossover vent and was directed to the reg. I am not a big fan of the crossover vent due to the issues noted. I need to stop in and say hi to Trimmer anyway. I will ask him if they gave him a hard time about it. I did look it up before I posted.
CAR 3
§ 3.430 Fuel system arrangement. Fuel systems shall be so arranged as to permit any one fuel pump to draw fuel from only one tank at a time. Gravity feed systems shall not supply fuel to any one engine from more than one tank at a time unless the tank air spaces are interconnected in such a manner as to assure that all interconnected tanks will feed equally.

DENNY

[Jetfever]

Steve, Brian
I always questioned why the Cub Crafters system had the crossover vent and was directed to the reg. I am not a big fan of the crossover vent due to the issues noted.

DENNY

Denny, although a crossover vent can cause the "issues noted", I have been indicating fuel transfer from 1 tank to the opposite fuel tank in the Off or Both position via the newer style Maul type fuel valve.

I am interested to hear if there are other issues with a crossover VENT line.

Thanks, Steve M.

[SMO22]

What valve is the Maule valve, are they still using this Piper / Anderson Brass valve http://www.skygeek.com/piper-492-009...el-select.html

Is this a Piper or Maule valve? I thought it was a Piper valve, maybe it's a Maule valve.

[DougG]

HI, Just a thought but if you are pulling fuel from both tanks and one tank is venting for, say a loose fuel cap, aren't you now venting from both tanks?
DougG

[Tp109]

Exactly.. that's another thing I had pondered, or you spring a leak in one tank, and now gravity does its thing.

[andya]

Remember that Trimmer STC calls for Positive pressure fuel caps for venting, I presume more of a vent than the original caps.

[walt.buskey]

Speaking from experience, the Dakota Cub valve also will cross-feed when in the OFF position.

Discovered this while testing connections after putting 5 gallons in each tank. Had a leak on one side, so started draining the 5 gallons from it. 5-gallon gas can I was draining into got full and the fuel didn't stop coming... eventually pulled all 10 gallons from both. Bit of a surprise.

[Tp109]

Speaking from experience, the Dakota Cub valve also will cross-feed when in the OFF position.

Discovered this while testing connections after putting 5 gallons in each tank. Had a leak on one side, so started draining the 5 gallons from it. 5-gallon gas can I was draining into got full and the fuel didn't stop coming... eventually pulled all 10 gallons from both. Bit of a surprise.

That's what I mentioned above, if you spring a leak on one side and the tanks are connected in BOTH position, than gravity will leak all the gas out, unless you catch it on the gauge. Maybe a science major might jump in on this hopefully and confirm, but I am recalling the Air Transat that became a glider over the Atlantic Ocean after unknowingly pumping all its fuel out of a leak on one side https://youtu.be/jjb63MBv_fo

In a PA-22 the engine needs around 17 ounces of fuel a minute to run at cruise, I would like to know if the tank without a leak would flow downhill to the engine at >17 ounces a minute and still be able to flow uphill back through the fuel selector and plumbing to the leaking gas tank trying to maintain equal volume with it?

[DougG]

I'm no science major but I think in the case of Air Transat the computer saw a fuel imbalance and auto transferred fuel to light side, unfortunately that side had and engine venting fuel due to a broken fuel line.

Andya, My Pacer has positive pressure cap on right side, not sure how it got there? I was out for a ride one day with full tanks when suddenly the rear hose on fitting started to leak, guess it was the cold? I turned for home and less than 30 min the tank went dry and I never burnt a drop, those caps work good at moving fuel.
DougG