REFLECTOR: FUEL FEED

[Jim Sower]

Tom,
My assymmetric flow drove me NUTS for nearly two years.  Almost always 
the right tank would transfer but the left one wouldn't (on several 
occasions it was the other way around).  I tried just about everything:
1.  Re-plumbed the vent system with larger lines.  Made it as 
symmetrical as possible.
Nothing.
Blew into the vents to see if they worked OK.  They did. 
Tested the gravity feed of each tank through the sump into bucket(s) and 
timed each side from full to empty.  No significant difference between 
tanks in gravity feed to empty.

2.  Shimmed the rudder(s) to ensure the ball was centered.
Nothing. 
Sometimes, if I kicked in full rudder and flew in a max crab for about 
10 minutes, the "reluctant" tank would get caught up a little.  Not a 
viable solution, but some help when the "eager" tank was running low and 
I really needed some fuel out of the reluctant tank.

3.  Sealed the fuel caps with several different products. 
Nothing. 
Taped over the fuel caps to totally seal them.
Nothing.

4.  Tried venting and not venting the sump tank
Nothing.

I went from pillar to post, trying everything anyone suggested (having 
done nearly all of it on my own already).  No change.  Right tank got 
down to 5 gal with left tank still indicating 20-25 gal.  There were 
times when the left tank /looked/ like it was trying to transfer, but 
didn't really.  That caused a flame out and I had to dead-stick out of 
Canada to PHN in Michigan.  I couldn't get *anything* to work.

Finally, I acquired a couple of [JC Whitney] electric selector valves 
and installed them between the strake and the sump as shutoff valves 
(capping off most of the nipples).  Now I can DE-select the eager tank 
and force the fuel pump to "suck" the fuel from the reluctant tank (this 
will NOT work if the sump tank is vented).  I still get assymmetric 
transfer, but I can fix it with the flip of a switch (the switch has a 
feature that lights an amber LED on the panes whenever one of the valves 
is closed.  I keep both tanks selected most of the time, and de-select 
the right one periodically to keep things even.  They also make 
convenient maintenance shut-offs.

I went after the problem in what I thought was ascending order of 
difficulty:  carefully checking out the vent system and insuring it 
worked OK,  checking rudder trim  and keeping the ball centered,   
sealing the fuel caps (first with tape to see if it was an issue at all, 
and then with various chemicals). 

The selector valves were what I got down to.  Installed them when all 
else failed.

Hope you have better luck ... Jim S.


Tom Martino wrote:

> Well, now that I'm in my test flying mode ... I will really be asking 
> a lot of questions.
>
>  
>
> Here are some of them, as they relate to my fuel system:
>
>  
>
> 1.  What makes the fuel tanks feed unevenly to the header 
> tank/engine?  (My right tank is feeding twice as fast as my right tank.)
>
>  
>
> 2.  Will that cause a problem when the fast-feeding tank runs out?
>
>  
>
> 3.  I used the larger vent lines for my tanks and tied them al 
> together with a manifold, then vented the entire system out through 
> the top of my firewall in the engine compartment (about four inches 
> below my naca duct).  Do you think the system gets enough venting there?
>
>  
>
> 4.  Is there a need for a "whistle" hole in any of the tank vents ... 
> for additional venting (like we do with the crankcase breather?
>
>  
>
> Any help is appreciated from my more experienced Velocitologists J
>
>  
>
>  
>
> Tom
>
> N173EX
>
> (A mere 6 hours)
>
>  
>
>  
>
>  
>
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