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

Jim Sower canarder at frontiernet.net
Fri Feb 18 14:01:26 CST 2005


I'm toying with the notion of eliminating the float sensor in my sump 
and stringing together several gems sensors to light a series of LEDs on 
the panel as the sump drains.
But I'm not supposed to ever be in the sump, am I :-( ... Jim S.

Alex Balic wrote:

> Tom-
> Do a google search for "gems level sensors" go to their web site, and 
> look for the solid state liquid level sensor- it uses an led emitter 
> to send light out against a clear prism- when there is air on the 
> other side of the prism, the light bounces back- if there is liquid on 
> the other side, it scatters into the liquid- the float type of sensors 
> (also made by gems) tend to have problems with leaking/sinking and 
> sticking I used to design industrial equipment, and we ended up 
> converting all of the float type switches to the prismatic type for 
> reliability.  I have one installed in my sump, but I don't have the 
> paper work handy- also- you can get them with normally open or 
> normally closed contacts depending on how you have your system wired.
>  
> Alex
>
>     -----Original Message-----
>     *From:* reflector-bounces at tvbf.org
>     [mailto:reflector-bounces at tvbf.org]*On Behalf Of *Tom Martino
>     *Sent:* Friday, February 18, 2005 8:51 AM
>     *To:* Velocity Aircraft Owners and Builders list
>     *Subject:* RE: REFLECTOR: Re: Reflector Digest, Vol 9,Issue
>     68-Fuel Feed-blinking low fuel warning
>
>     Isn't there a simple on/off fuel sensor that can be installed? 
>     "ON" when fuel touches it, and "OFF" when fuel drops below a
>     certain level?  Like the sensors in RV water tanks?
>
>      
>
>     -----Original Message-----
>     *From:* Carruth, Joel L [mailto:joel.l.carruth at lmco.com]
>     *Sent:* Friday, February 18, 2005 7:34 AM
>     *To:* Velocity Aircraft Owners and Builders list
>     *Subject:* RE: REFLECTOR: Re: Reflector Digest, Vol 9,Issue
>     68-Fuel Feed-blinking low fuel warning [heur]
>
>      
>
>     Jeepers!  I've been listening to the problems with unporting,
>     greasing the o-rings, false sump indications over 10K, and "no
>     way" of knowing what situation your fuel is in, and frankly it
>     leaves me a little worried about my future fuel system!!!  On one
>     hand, I tend to agree with Scott Baker and don't change the
>     design, but on the other, you all have convinced me that there is
>     room for some tweaking!  I just don't believe in guessing about my
>     fuel condition.
>
>      
>
>     In particular, I plan to do away with the float switch and install
>     a fuel-level sensor in the sump. Secondly, a simple flow switch in
>     each line from the mains would give you vital information about
>     which way the fuel is going! This wouldn't be an expensive flow
>     meter, but a simple flow switch with indicator. I think Omega
>     sells these for around $130 each. Two switches, plus the
>     fuel-level sensor would take the guess work out of fuel management
>     and allow the pilot to make corrections as needed... before the
>     fan goes quiet!!  
>
>      
>
>     '96 SEFG
>
>      
>
>     */Joel Carruth/*
>
>     Lockheed Martin
>
>     JSF - Pilot System Software
>
>     W: (817) 763-4337
>
>     Fax: (817) 777-8378
>
>     joel.l.carruth at lmco.com
>
>      
>
>     ------------------------------------------------------------------------
>
>     *From:* reflector-bounces at tvbf.org
>     [mailto:reflector-bounces at tvbf.org] *On Behalf Of *Jim Sower
>     *Sent:* Thursday, February 17, 2005 9:02 PM
>     *To:* Velocity Aircraft Owners and Builders list
>     *Subject:* Re: REFLECTOR: Re: Reflector Digest, Vol 9, Issue
>     68-Fuel Feed-blinking low fuel warning
>
>      
>
>     <... 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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