Fuel Lines from Tanks?

[HighWing]

In my experience, the fuel flow set-up from the wing tanks to the header tanks is one of the most "To each his own" discussions in both the old email lists and the forums. Personally, I see no reason for the possible restrictions resulting from fuel shut off valves, but I do like the clear glass fuel filters. I like the filters because I can see the fuel. The one time I did the actual in flight low fuel indicator system check, I was able to see a lot because of the translucent vent lines and the fuel filters. The fuel valves between wing tanks and header tank originally began appearing in the fleet because of the typical uneven fuel flow from the two tanks which bothered some of the guys. One particular time comes to mind on one of our cross country flights when a new guy to the group flew from No. Callif. and joined us at Elk River in Idaho. He was almost beyond panic because of what he was seeing in the sight gauges. The group got busy and undid his system enough to do a fuel flow test. No problem - at all. What he was seeing was likely due to the typical one wing low flight tendency in our airplanes. I never paid attention to it because it always evened out in the end. This, I guess, due to the two or three long cross country flights each year in company with the flying buddies, none of whom had valves other than the main shut off valve. (For maintenance needs , I simply use clamps.)

[avidflyer]

About a week ago, I did a fuel flow test on my Avid MK IV. I have fuel valves, then 1/4" fuel lines from both wing tanks to the header tank with no filters in those lines. From the header tank forward, I have a 1/4" ID fuel line, an electric fuel pump, and a fuel filter under the instrument panel, and a fuel valve there as well. 1/4" ID fuel line from that valve to the single Bing carb on the Jabiru engine. With about 7 gallons in the right tank, and left tank shut off, I measured about 7.5 gallons of fuel flow per hour with gravity feed. I had the float bowl off and captured the fuel as it came out the bottom of the carb. Kind of shows to me that 3/8" line would be very large. I would not put a filter between the wing tank and header tank. Had one off field landing because of that. You most likely have fuel screens in your fuel tank, the header tank is a large gascolator, and having a filter ahead of that to capture anything the header tank and fuel screen missed seems like a good idea to me. But as was mentioned, to each his own. Also, if you have the ram air tubes on your fuel tank caps, that will increase your fuel flow while in flight compared to just gravity feed. I'm guessing you have a fuel pump in the mix as well..... JImChuk

[kitfox2009]

Hi Jim
When I did my fuel flow test 6 years ago I remember blocking up the main wheels and tying down the tail in order to simulate a maximum climb profile. Don't recall the exact flow rate but it was considerably more than a 912 can use. I could check records.
I do have finger screens. Never found anything in them.
Shut offs are ball valves with same bore size as the hose.
I have a master shut off on the consul ahead of the header tank.
I have the standard 912 mechanical fuel pump.
I do not have an electric auxiliary pump. I have always thought in the event of a pump failure that gravity feed would supply at least enough fuel for sustained flight.
No I have not done a flow test at the carbs.
Am I mistaken thinking the fuel will flow through a faulty pump.
This should invoke an interesting discussion.
Looking forward to others experience.
Don

[Dusty]

My 912 had a pump failure that restricted the fuel flow, it kept running at low power.I didn't see the dismantled pump but was told a valve part had separated and restricted the flow.I now run a one way valve that will allow the electric pump to bypass the original if this happens again.

[kmach]

I have heard, somewhere and awhile ago, of the rotax mechanical pump reducing flow when dirt or debris blocks a small screen in it.

This could possibly be on the older pump style.

Should not be an issue if you have a filter before it and use clean filtered fuel.

[jiott]

I have the newer fuel pump on my 912uls and I tested gravity fuel flow thru the fuel pump that was not running but was in good condition. Flow thru the pump was definitely less than when measured with the line disconnected just before the pump. I have no filters or shut-off valves in the lines from tanks to header; one shut-off in the console; one inline filter just before the fuel pump; no electric boost pump. A non-running pump is a definite restriction and I would think probably would prevent WOT operation, but would still allow the engine to run continuosly at a lower throttle setting. Of course this could all change if the pump were damaged and loose debris causes additional blockages.