no fuel flow during test

[Wheels]

My Kitfox model IV 1200 doesn't have an aux pump. I was thinking of putting one in.
I was told that a certified engine should flow fuel from the pump even if the pump fails, its a function of gravity. I have seen stuff on the forum about testing fuel flow so, I decided to test the theory and was amazed that NO fuel comes out of the "fuel out" side of the pump when I disconnected the hose.:eek:
The fuel shutoff is in the "on" position, the tanks have over 1/4 full and the tail was up on a saw horse in the flying attitude.
I tipped the nose of the plane almost to the floor before fuel started to flow freely from the pump.
My header tank is located on the floor behind the passenger seat. It IS lower than the pump but doesn't the fuel in the wing tanks create enough head pressure to push flow out of the header tank to the pump?
Do I NEED a header tank?

[jtpitkin06]

Going without a header tank is not advisable.
Let’s suppose you decide to forego the header tank and put in two lines, one from each tank and join them at a “T”.
As you make your landing approach you are a bit high so you decide to slip a bit.
The fuel in the lower wing sloshes to the lowest point away from the fuel supply port in the tank.
The fuel in the higher wing flows down to the “T” fitting and tries to go back up the opposite fuel line into the low tank. In doing so it creates a siphon action at the “T” fitting and fuel may be restricted to the engine.


Adding a vented header tank where the two fuel supply lines join prevents the siphon action. In the above slip to landing scenario, fuel will flow from the high wing tank into the header, and at the same time some fuel will try to flow across from the high tank to the low tank. However, with the header tank the siphon action is broken with a vent line. Fuel flows unrestricted to the engine.
The other scenario is where you are doing a long and steep descent with low fuel quantity in the wings. Although the Kitfox header tank allows for several minutes of steep descent with the engine at idle, it is still possible in rare circumstances to run the header tank out of fuel. One builder reported such an occurrence after crossing the Sierra and making a long steep descent to the central California valley. Raising the nose to a normal descent allowed the header tank to refill. This appears to occur only with very low fuel in the wings.



Installing a header tank low fuel warning light may be helpful.


To answer your other question about the free flow of fuel through the pump: That depends on the pump design. Many fuel pumps have check valves that prevent backwards flow. Mechanicals almost always and electrics maybe yes and maybe no. The head pressure from the tank must be sufficient to push the check valve spring open. Some pumps are designed to close the check valve only when the pump is running, the rest of the time the pump is in free flow mode. You'll need to check your fuel pump specifications to see if it is a free flow design.



Because of the position of the carburetors on top of the Rotax engine it is possible to get the carbs higher than the fuel tanks when in a very steep climb. That's why the Rotax installation should include a low mounted fuel pump.


For engine installations with low mounted carburetors like the Lycoming or Continental it is almost impossible to get the carburetor higher than the wing tanks in a steep climb.


John Pitkin
Greenville, TX

[Dorsal]

Do you get good flow if you pull the line before the pump?

[HighWing]

John's comment is on the mark. In the old days, before the vent line was put in the system there were several instances where there were fuel flow issues in uncoordinated flight. The vent line corrected that. Can't comment on the mechanical pump. One question I have always had though, if the mechanical pump fails, will it pass the aux pump fuel to the carburetors, or will it simply allow it to run into the crank case. I have heard stories like that with regard to diaphragm pumps.
Lowell

[Wheels]

Thank you John. That makes total sense. I will keep the header tank. It is vented to the right wing tank. There is a "free" nipple at the bottom of the header and I can run a fuel return line to it easily but was wondering if it's ok to put a fuel return into a "full" header tank or should I run it to the right tank like the vent from the header. It just seems like a vent line to the header tank would have to overcome the weight of fuel in the header and the wing tank, and with the vent going into the bottom of the tank I would need a check valve and the restrictor fitting to keep from backflowing fuel into the carburators. This is all part of my months long search to the problem of fuel venting from the carburators at low idle.

The new rubber isolators are going into the mounts today. That should quiet some vibration.

[Dorsal]

Fuel return can go directly to the header tank, its a closed system so the pressure is balanced.

[Wheels]

Thank you Dorsal. I am ignorant of the term "closed system" can you explain it ... "as if to a child."

[Dorsal]

Sorry, that just means that the fuel is coming from the header tank and returning to the header tank in a closed loop. Given the pressure at the supply side and return are the same the pump will see no static differential pressure. This would be true even if you return to the wing tank as then the closed loop includes the headertank and lines to the main tanks.

[Wheels]

Ok, Got it.
I think I will go ahead and get the facet fuel pump on order. I'll have my mechanic research the requirements for check valve placement and power supply requirements, pressure regulation, star alignment etc. etc.
Thank you so much for your reply.
Jay

[Dorsal]

I am still curios if you get good flow when you pull the line going into the fuel pump?

[HighWing]

I too am curious. What engine are your running and is a return line absolutely necessary for your application. This comes up because the header tank is designed with two ports near the bottom of the tank. One is directly on the bottom which is designed for a quick drain that can be accessed through the bottom skin. Then the forward facing port is for the fuel line to the valve and engine. The higher placement allows sediment and water to have a place to settle out keeping it from the carburetors. I guess you could T off of one of these ports for a third line to the header, but I don't think I would be comfortable eliminating the quick drain for the sake of a return line or putting the fuel line proper on the bottom of the tank.
Lowell

[Wheels]

Hello, Highwing, I am flying a 912F in a kitfox model IV. I have the new aluminum header tank and the rotax installation manual calls for the return line. I have the quick drain in the bottom of the plane but I also have an extra provision on the left side of the tank near the bottom so getting the line to it is not going to cost me any of my connections.

I am ordering the facet fuel pump tomorrow and my mechanic is reseaching the right way to ensure that it works without overpressurizing the carbs, acting like a check valve when its supposed to be delivering fuel, or any other unwanted activities that I have heard tell of in the recent past. Now if I could only figure out how to make it ... weightless!

[Lion8]

Today I did my fuel flow test. I piped the path with 3/8 Rubber lines to the alum header with no valves. From header to the firewall is 3/8 alum. One 1/4 turn stop valve in a console. From the firewall fitting a 45 to a gascolator . I pulled the mains up on my split 40ft. extension ladder to 25 deg. nose high(Thank you John P.). Once I wet the whole system, I ran my time test. I got 16.5 gph flow rate.

[rogerh12]

If you want a simple, low cost, adjustable fuel pressure regulator, I suggest the one I used on my 601hds, to set the Ellison Injector carb to 2 psi from the fuel pump, which was at 5 psi:

http://www.performanceplusconnection.com/Item/Fuel_Pressure_Regulator_Gas_6PSI

Note: Some fuel pumps are flow-through, good for use as a booster pump, but other will stop the fuel flow when the power is shut off.
Hope this helps
Roger