Header Tank Vent Line

[vetdrem]

I have a model 3 with a 912 UL, 13 gal tank in right wing, 6 gal tank in left wing and an aluminum header tank behind the seat that is vented to the top of the right wing tank. I fly with the right tank on service and the left tank isolated.

I have experienced the deafening silence when fuel level gets low and the outlet gets unported.

I would like to install a low fuel warning in the header tank vent line, but I am concerned that I will get a lot of spurious alarms.

I have been watching the fuel level in the vent line, and I would assume that the level should be equal to the right tank level, but it never is. I normally see a level that is a couple inches lower that the bottom of the wing tank.

Could the wing tank being pressurized cause this indication, and if I install the low fuel warning switch in the header tank vent line, will it operate correctly?

thanks

Louie

[n85ae]

It won't work right in the vent line, it has to be in the feed side. The vent
line ends up handling mostly vapor. You would think fuel, but it's really not.
Somebody who can explain fluid and hydraulics better than me could probably
explain it so it makes sense. I just know it doesn't work.

Regards,
Jeff

[jiott]

I installed the Kitfox factory supplied fuel sensor kit in my header tank vent line, just above the top of the header tank. It works fine in my SS7 and the vent line stays full of fuel as it should.

[HighWing]

I have had a vent line Low fuel system in both my Model IVs. My system consists of black auto fuel line for the flow line and the clear Tygon line for the vent. I also have a glass fuel filter right above the quarter windows on both sides for a secondary visual check.

On the way back from Idaho once I skipped the Winnemucca fuel stop because of favorable winds. As I crossed the Sierras, I peaked at about 10,000 ft. and began the descent to Camreon Park - 1300 ft. ~ thirty minutes flight time. I was approaching the critical nose down angle because of the rear fuel tank port in the earlier Kitfoxes. I thought I would test the low fuel warning system, so carefully monitored the fuel. After the main tanks unported, I watched as the fuel level in the vent line descended - it does work exactly like the sight tubes. Then as the level in the vent line aproached the clear fuel filters, I saw the reduction of the level of the fuel in the glass filter. A few minutes later, the low fuel indicator triggered and I got the flashing red light on the panel. Leveling the plane a bit reported the tanks and the red flashing light returned to green and I continued to landing. I had estimated about three gallons in each tank and that was confirmed after landing.

The systems do work.

[Lion8]

Haven't yet had mine up since I saved her from the sad fate of the 'cash for your scrap' men. Repowered with a Jabiru 2200. This past summer I made a set of ramps at 25 deg. Hoisted the plane up to the 25deg nose up angle, Wings were not mounted yet so I rigged a Beer keg at wing height and hosed it down to the header tank. I also have a glass filter to the rear of the right seat so I can see it. I have a tiny red LED indictor light on the panel that will come on when the header tank is at 20min flight time left.
The fuel flow (100LL, not Beer) at somewhere around 16 gph gravity flow out of the gascolator. The indicator light worked as expected. I originally had a fuel tank selector valve installed but see no real reason for it so it is replaced with a brass 'T'. I use the clear blue line on my Trike but inside the cabin of the Kitfox, I use 'Barricade Hose' to the header. From the header to the firewall is alum. tubing. I hope I can pass along some good tips. -Tom