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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