Header Tank Venting

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Header Tank Venting

Postby sonex293 » Wed Mar 28, 2018 11:33 am

What is the common practice for venting on the header tank? There seems to be two schools of thought. First, have large 1/2" lines from the header to main tanks for vent and fuel flow. Second, have a dedicated vent line back to the main tanks, which requires drilling a new hole in the already mounted main tanks. If it makes a difference, I may be using a fuel injected engine.

==Michael
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Re: Header Tank Venting

Postby BucF16 » Wed Mar 28, 2018 11:49 am

Michael, I had the same Question! I bought Steve Henry's hearer tank and there is a tapped "Vent" hole beside the main tank holes. Since I don't have the Firewall Forward plans, I was at a loss. We must be at the same place.

Thanks to all in advance!
Bruce
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Re: Header Tank Venting

Postby BucF16 » Wed Mar 28, 2018 11:57 am

Here is a picture and a stock JA header tank. What think I see are the 2 lines from each tank, and the return line from the engine, But no vent to the header. So anyone please correct my if I'm wrong.

Thanks
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Bruce Johnson Highlander # 393
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Re: Header Tank Venting

Postby danerazz » Wed Mar 28, 2018 5:12 pm

Generally the issue with the header is when the mains are low and fuel sloshes forward (think during a long descent), the pickup points unport and the engine is running off ONLY the fuel in the header. This draws a bunch of air into the header. Then, when you pitch up and the fuel ports are submerged in the mains, the fuel has to trade places with the air in the header. This can actually cause an “airlock” that prevents the fuel from getting to the header quickly.

If you put a third line from the top of the header to the top of one of the mains (the air space at the top) then the air goes out there, and the fuel can quickly refill the header.

Kitfox actually had a service bulletin a couple years ago that addressed exactly this, asking owners to add a vent as described.
Dane

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Re: Header Tank Venting

Postby BucF16 » Thu Mar 29, 2018 8:03 am

Thanks Dane, That makes sense.

Now, since I have fiberglass tanks, do I drill and tap the fiberglass or hysol in an insert that is already drilled and taped? And the right tank would be the logical choice.

Cheers,
Bruce
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Re: Header Tank Venting

Postby alan » Thu Mar 29, 2018 9:07 am

I've been flying my Highlander for almost 13 years now, more than 800hrs, and I have found that the tanks will naturally vent back to one tank or the other as long as both tanks are open. For the first flight of the day, after the airplane has set for a few days with full tanks, I open both tanks for the preflight, and I can hear the air bubble up to the starboard tank. After engine start I close one tank valve and fly for an hour before switching tanks. After that second hour I run with both open. I do it that way because if both tanks are close to full then, as fuel transfers slightly from side to side in flight, more fuel vents over the side. It might not be a factor with the different caps on the metal tanks but it sure was with the pressure vented caps of the fiberglass tanks.

I found out, early on, that if I run a tank empty the engine would run a little rough if I closed that valve and opened the other and tried to fly off the other tank, but if I left both valves open then the air in the header vented to the empty tank and all was well.

In short, a dedicated vent line is an unnecessary complication.

Have fun, y'all. :-)

Alan
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Re: Header Tank Venting

Postby danerazz » Thu Mar 29, 2018 5:25 pm

BucF16 wrote:Thanks Dane, That makes sense.

Now, since I have fiberglass tanks, do I drill and tap the fiberglass or hysol in an insert that is already drilled and taped? And the right tank would be the logical choice.

Cheers,
Bruce



I put brass bushings for the pickups and quick drains in. I went to Lowe’s plane...I mean home...improvement and bought the appropriate size brass reducer bushings in their fuel plumbing section, cut cross slots to allow flow all the way to the surface of the tank, used NPT taps to thread the holes I drilled, cut some notches in the brass threads for epoxy to grip, then used West System epoxy and flox to glue them in place and make a slurry fillet around the protruding head.

I put two quick drains in each tank: one near the fuel pickup and one in the “triangle” that hangs down outboard over the diagonal brace, since that just strikes me as an un-drainable sump. Reading the preceding post, I may not add the vent as it makes sense.

I have to say that a forum member, Wes, actually gave me the ideas for how to accomplish this. Search his posts on here and there are pictures.
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