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

[Alex Balic]

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




----------------------------------------------------------------------------
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  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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