REFLECTOR: Re: Reflector Digest, Vol 9, Issue 68-Fuel Feed-blinking low fuel warning

Jim Sower canarder at frontiernet.net
Thu Feb 17 21:01:23 CST 2005


<... The only way I could see that happening is if the flow from the 
mains is somehow restricted due to inadequate venting, and that the fuel 
pump is pulling fuel out the sump tank and the sump vent line is letting 
in air into the sump lowering the fuel level. ...>


      Bingo!!

And once your sump fuel level falls low enough to light the low fuel 
light, you never know how much usable fuel you have until that light 
goes out.  The mains might be providing 95% of demand in which you'll 
make it home with a gallon or two in the sump.  Then again, they might 
be only providing 50% of demand in which case you flame out in under an 
hour.  If the strakes are only providing 25% of demand, you've got about 
half an hour of fuel. 
And you have NO WAY of knowing which situation you're in until either 
you get where you're going and LOOK at the sump, or the fan goes quiet.

Go ahead and ask me how I know this ... Jim S.


Chuck Harbert wrote:

> To John Dibble:
>
> This is very strange that it only occurs intermittingly at high 
> altitudes, unless it is just a intermittent bad electrical connection 
> or switch. Do you have the same type of low fuel switch that I have ( 
> mine is green and floats in the sump tank)? I installed mine on the 
> pilot side of the sump near the top. I didn't quite understand your 
> description and thot maybe it was a different type switch. Are you 
> sure the warning light itself isn't just loose in it's socket?
>
> I'm trying to understand what changes at higher altitude that would 
> affect the low fuel switch. The only thing I could think of was that 
> atmospheric pressure drops, so the sump tank could possibly expand a 
> little I guess. Do you have a sump tank vent line and the main tank 
> vent lines per plans?
>
> I'm assuming that you have pretty much ruled out the possibility that 
> the sump tank is partially emptying and that the low fuel switch is 
> working properly? The only way I could see that happenning is if the 
> flow from the mains is somehow restricted due to inadequate venting, 
> and that the fuel pump is pulling fuel out the sump tank and the sump 
> vent line is letting in air into the sump lowering the fuel level.
>
> Chuck H
>
>
>


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