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rrhoyt(at)ieee.org Guest
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Posted: Fri Feb 10, 2006 7:27 pm Post subject: Fuel Line Bubbles |
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I have noticed a disconcerting phenomena in the fuel supply lines of
my 912UL. i.e. Bubbles of sizeable dimensions. These bubbles are
showing up at the carburetors after the 912 fuel pump. The fuel pump
provides 15 gal per hour so there appears to be sufficient fuel for
the engine. The trouble is that they trip the ESI fuel pressure
alarm by allowing the fuel pressure to go to zero. I presume this
occurs as the bubble passes into the carburetor.
Is there any experience in the group with this phenomena.
The fuel supply to the pump is about 18 inches below the pump. The
fuel supply is from a sediment bowl that is completely full during
this phenomena. There are no leaks in the fuel system.
Do the bubbles come from the pumping energy of the pump agitating the fuel?
Are they from the vacuum in the 18 inch lift of the fuel?
Will they cause the pump to fail pumping fuel and only pump vapor?
Is the fuel pump showing initial signs of failure?
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John Hauck

Joined: 09 Jan 2006 Posts: 4639 Location: Titus, Alabama (hauck's holler)
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Posted: Fri Feb 10, 2006 7:54 pm Post subject: Fuel Line Bubbles |
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| Is there any experience in the group with this phenomena.
Hi Ron H:
Best way to fix bubbles in the fuel line is change from transparent
fuel line to top quality Gates neoprene fuel line. Not only will you
not have to worry about bubbles in the fuel line, but you will have a
fuel line that is much more durable and reliable than transparent
plastic "UL" lines.
The Bing carbs are designed to seperate air from fuel prior to entry
into the main jet well, on both 4 and 2 strokes.
I don't use a fuel pressure sender and display on my 912ULS
application, so have no idea if my pressure is going to zero or not.
However, the engine driven fuel pump on the 912 series engines is more
than adequate to lift fuel several feet to the carbs with no problem.
Take care,
john h
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_________________ John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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Steve Boetto
Joined: 11 Jan 2006 Posts: 365
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Posted: Sat Feb 11, 2006 3:56 am Post subject: Fuel Line Bubbles |
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In a message dated 2/10/2006 10:54:49 PM Eastern Standard Time,
jhauck(at)elmore.rr.com writes:
Quote: | Best way to fix bubbles in the fuel line is change from transparent
fuel line to top quality Gates neoprene fuel line
|
Thanks John, Wish you had taught me that theory when I was back in high
school. Had an ugly girlfriend. Who knows how things would have worked out.
Sorry, Couldn't help it. I think this is a common phenomenon. Not sure why,
maybe our engine Gurus can explain it. I have seen it on everything from model
AC to my 4 barrel Holly on my Jeep. On my FF 447 the clear plastic filter
bowl is always full of air with bubbles from the fuel pump to the carb. I always
assumed that the float bowl was responsible for leveling out the fuel and
filling in the gaps kinda like a capacitor in a circuit.
Steve do not archive
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slyck(at)frontiernet.net Guest
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Posted: Sat Feb 11, 2006 5:08 am Post subject: Fuel Line Bubbles |
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Having the fuel pump lift the fuel from the tank naturally reduces the
pressure causing some of the more volatile constituents of the gas to
"boil" out. Cures: 1. JH's opaque line, 2. pump at tank level, 3,
slightly pressurized tank, 4. larger diameter fittings at tank and
larger diameter hose will slow the rate of pressure drop and perhaps
lessen bubbles.
On 11, Feb 2006, at 6:52 AM, N27SB(at)aol.com wrote:
Quote: |
In a message dated 2/10/2006 10:54:49 PM Eastern Standard Time,
jhauck(at)elmore.rr.com writes:
> Best way to fix bubbles in the fuel line is change from transparent
> fuel line to top quality Gates neoprene fuel line
Thanks John, Wish you had taught me that theory when I was back in high
school. Had an ugly girlfriend. Who knows how things would have worked
out.
Sorry, Couldn't help it. I think this is a common phenomenon. Not
sure why,
maybe our engine Gurus can explain it. I have seen it on everything
from model
AC to my 4 barrel Holly on my Jeep. On my FF 447 the clear plastic
filter
bowl is always full of air with bubbles from the fuel pump to the
carb. I always
assumed that the float bowl was responsible for leveling out the fuel
and
filling in the gaps kinda like a capacitor in a circuit.
Steve do not archive
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slyck(at)frontiernet.net Guest
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Posted: Sat Feb 11, 2006 5:31 am Post subject: Fuel Line Bubbles |
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Also: use fuel with lower vapor pressure such as avgas or summer
blend mogas
-BB
Quote: |
Having the fuel pump lift the fuel from the tank naturally reduces the
pressure causing some of the more volatile constituents of the gas to
"boil" out. Cures: 1. JH's opaque line, 2. pump at tank level, 3,
slightly pressurized tank, 4. larger diameter fittings at tank and
larger diameter hose will slow the rate of pressure drop and perhaps
lessen bubbles.
>
>
>
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rrhoyt(at)ieee.org Guest
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Posted: Sat Feb 11, 2006 8:28 am Post subject: Fuel Line Bubbles |
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John
Thanks for the reply.
The only reason I know of the existence of the bubbles is that I went
looking for the cause of the fuel alarm. Otherwise my entire fuel
system is made of AN fittings with alum. tubing or neoprene fuel line
with fire covering. I disconnected one of the carburetors to connect
a clear tube.
At 09:53 PM 2/10/2006, you wrote:
Quote: |
| Is there any experience in the group with this phenomena.
Hi Ron H:
Best way to fix bubbles in the fuel line is change from transparent
fuel line to top quality Gates neoprene fuel line. Not only will you
not have to worry about bubbles in the fuel line, but you will have a
fuel line that is much more durable and reliable than transparent
plastic "UL" lines.
The Bing carbs are designed to seperate air from fuel prior to entry
into the main jet well, on both 4 and 2 strokes.
I don't use a fuel pressure sender and display on my 912ULS
application, so have no idea if my pressure is going to zero or not.
However, the engine driven fuel pump on the 912 series engines is more
than adequate to lift fuel several feet to the carbs with no problem.
Take care,
john h
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rrhoyt(at)ieee.org Guest
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Posted: Sat Feb 11, 2006 8:34 am Post subject: Fuel Line Bubbles |
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This could explain why I have had the alarms only recently. I use
non-oxiginated mogas from a local automotive gas station.
Ron
At 07:29 AM 2/11/2006, you wrote:
Quote: |
Also: use fuel with lower vapor pressure such as avgas or summer
blend mogas
-BB
>
> Having the fuel pump lift the fuel from the tank naturally reduces the
> pressure causing some of the more volatile constituents of the gas to
> "boil" out. Cures: 1. JH's opaque line, 2. pump at tank level, 3,
> slightly pressurized tank, 4. larger diameter fittings at tank and
> larger diameter hose will slow the rate of pressure drop and perhaps
> lessen bubbles.
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jlbaker(at)telepath.com Guest
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Posted: Sat Feb 11, 2006 12:27 pm Post subject: Fuel Line Bubbles |
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Quote: | > Best way to fix bubbles in the fuel line is change from
transparent
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Quote: | > fuel line to top quality Gates neoprene fuel line
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I just can't let this pass.....why? Is this somehow connected to Erwin
Schrodinger's paradoxical cat or Heisenberg's uncertainty principle?
If you cannot observe the bubbles they're not there? Surely the
transparent fuel line isn't that porous? Experimental data to back this
up?
Yes, I know the above relates to quantum states, not the
macroscopic world, but you get the drift.....
Jim Baker
580.788.2779
'71 SV, 492TC
Elmore City, OK
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John Hauck

Joined: 09 Jan 2006 Posts: 4639 Location: Titus, Alabama (hauck's holler)
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Posted: Sat Feb 11, 2006 1:17 pm Post subject: Fuel Line Bubbles |
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| > > Best way to fix bubbles in the fuel line is change from
| transparent
| > > fuel line to top quality Gates neoprene fuel line
|
| I just can't let this pass.....why? Is this somehow connected to
Erwin
| Schrodinger's paradoxical cat or Heisenberg's uncertainty principle?
| If you cannot observe the bubbles they're not there? Surely the
| transparent fuel line isn't that porous? Experimental data to back
this
| up?
|
| Yes, I know the above relates to quantum states, not the
| macroscopic world, but you get the drift.....
|
|
| Jim Baker
|
Hi Jim:
What I was saying was the bubbles are going to be there no matter what
you do. The bubbles pose no problem to me, in that they do not affect
my engines performance. Bing took care of the problem by providing a
system to seperate the air from the fuel before it enters the main jet
well.
Nope.........I didn't say or intend that the bubbles were not there if
I could not see them.
Did not say the plastic line was porous.
Have no experimental data to back up what I said.
I do have the experience with my engines and fuel systems though, to
more than adequately back it up.
Nope, don't get the drift. Not looking for it.
Take care,
john h
hauck's holler, alabama
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_________________ John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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a58r(at)verizon.net Guest
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Posted: Sat Feb 11, 2006 2:39 pm Post subject: Fuel Line Bubbles |
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The use of non-transparent fuel line may have its roots in the radio
show, Click & Clack, wherein they sometimes advise placing black tape
over a gage to "eliminate" the suspected out-of-tolerance reading.
And while you are replacing the see-through line, buy one of those
Magic Mile Maker thing-ys that clamps around the fuel line,
decreasing fuel usage.
always looking on the wild side,
Bob N.
do not archive
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Steven Green
Joined: 05 Feb 2006 Posts: 118
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Posted: Sat Feb 11, 2006 2:59 pm Post subject: Fuel Line Bubbles |
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Ron,
The bubbles are possibly of some concern, the fuel pressure loss is
definitely something to be concerned about. My fuel level is 30 + inches
below the fuel pump at times and my fuel pressure stays very constant. I
also use EIS to monitor fuel pressure and have never had it to alarm with
the engine running. Is your tank properly vented? Do you have a fuel
filter on the suction side of the pump and if so is it located down at the
tank or close to the pump? How often does it alarm? Any kinks or callapsed
hose on the suction side?
Steven Green
MkIII 912S
---
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rrhoyt(at)ieee.org Guest
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Posted: Sat Feb 11, 2006 7:53 pm Post subject: Fuel Line Bubbles |
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Steve
You wrote:
" Is your tank properly vented? "
Yes. I measured 2 inches of water pressure on a
manometer taped into the fuel tank vents during level flight.
"Do you have a fuel filter on the suction side of the pump and if so
is it located down at the tank or close to the pump?"
Yes I normally have a fuel filter in the sentiment
bowl. However, I removed it for the testing. So it would not impact
the observations.
"How often does it alarm?"
The alarms seem to increase as the fuel level in the tank
goes down. The alarms first occur at about 10.9 gal out of 13.4 gal
at the start of the flight. The alarm flashed so fast I couldn't see
what the parameter was. Later (about 30 min.) the alarm stayed on
long enough to identify it as the fuel pressure. Later still (about
35 min) it stayed on long enough for me to watch the fuel pressure
fluctuate between 0 and 2 and back to 0 pounds of pressure. I headed
back to the airport then. The alarm was flashing randomly and
frequently a couple of times a minuite. There was about 8.5 gal of
fuel in the tanks. The tanks are in the wing roots. All my testing
was done on the ground with the remaining fuel in the tanks.
The alarming was frequent enough that I turned on an auxiliary
electric fuel pump when I entered the pattern. The alarms
stopped. The fuel pressure no longer fluctuated around 4 to 5 psi
but stabilized at 5 psi. The electric pump is about 4 inched from
the sentiment bowl at the same level.
" Any kinks or collapsed hose on the suction side?"
I inspected for this, however, the fire protection covering
over the neoprene hoses makes this hard to determine. In view of the
last question and the electric fuel pump action, this could be a
problem area. Tomorrow I will determine the adequacy of the hoses to
the engine!
Thanks
Ron
At 05:10 PM 2/11/2006, you wrote:
[quote]
Ron,
The bubbles are possibly of some concern, the fuel pressure loss is
definitely something to be concerned about. My fuel level is 30 + inches
below the fuel pump at times and my fuel pressure stays very constant. I
also use EIS to monitor fuel pressure and have never had it to alarm with
the engine running. Is your tank properly vented? Do you have a fuel
filter on the suction side of the pump and if so is it located down at the
tank or close to the pump? How often does it alarm? Any kinks or callapsed
hose on the suction side?
Steven Green
MkIII 912S
---
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jbhart(at)onlyinternet.ne Guest
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Posted: Sun Feb 12, 2006 7:38 am Post subject: Fuel Line Bubbles |
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At 09:57 PM 2/11/06 -0600, you wrote:
Ron,
It might help to insert a short section of clear fuel line just before your
engine pump. If you do not see bubbles here but continue to see them after
the pump, you may have a diaphragm starting to go bad, a pin hole leak on
the suction side of the casting or loose screws holding the pump together.
If you see bubbles before the engine pump, it indicates that there is a
failure some where before the engine pump. You may have a small crack in
the fuel line, or a connector that is not tight, etc. If you turn on your
electric pump and the bubbles disappear, it is a further indication of a
small suction leak between the electric fuel pump and the engine pump.
Also there was a service bulletin out on your engine model describing cracks
found in engine pump inlet region. You may want to check out:
http://www.auf.asn.au/airworthiness/912031.pdf
Hope this helps you out.
Jack B. Hart FF004
Winchester, IN
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John Hauck

Joined: 09 Jan 2006 Posts: 4639 Location: Titus, Alabama (hauck's holler)
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Posted: Sun Feb 12, 2006 7:57 am Post subject: Fuel Line Bubbles |
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| Also there was a service bulletin out on your engine model
describing cracks
| found in engine pump inlet region. You may want to check out:
|
| http://www.auf.asn.au/airworthiness/912031.pdf
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| Hope this helps you out.
|
| Jack B. Hart FF004
| Winchester, IN
Ron/Jack/Gang:
After rereading the SB, looks like activation of the electric fuel
pump, with engine not running, would be a good way to check for
leaks..
I remember in the old days of ultralighting with transparent fuel
line, spending a lot of time chasing air bubbles to no avail.
Eric Tucker, Rotax, recommended using a fuel pressure gauge to monitor
fuel pressure.
Was thinking, that's dangerous for me, it might be a good idea to
check the fuel pressure sender for the EIS. If the warning is raising
Hell and the engine is continuing to run normally, could be indication
there is a problem with your fuel pressure monitor.
Just trying to help.
john h
MKIII/912ULS
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_________________ John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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jbhart(at)onlyinternet.ne Guest
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Posted: Mon Feb 13, 2006 5:35 am Post subject: Fuel Line Bubbles |
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testing
do not archive
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David.Lehman

Joined: 10 Jan 2006 Posts: 265 Location: "Lovely" Fresno CA
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Posted: Mon Feb 13, 2006 5:43 am Post subject: Fuel Line Bubbles |
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No bubbles...
On 2/13/06, Jack B. Hart <jbhart(at)onlyinternet.net> wrote:
Quote: |
testing
do not archive
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_________________ ô¿ô
"Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute."
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by0ung(at)brigham.net Guest
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Posted: Mon Feb 13, 2006 8:15 am Post subject: fuel line bubbles |
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If you have bubbles in the fuel lines the first thing I would do is a vacuum
test. Close off the supply and put a vacuum on the line going to the
carbs,, next do a pressure test, because of the directional valves in the
fuel pump you will have to apply the pressure from the tank side of the
pump.
Next compare the pressure on your pump to the pressure the pump should
provide..
Boyd
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John Bickham
Joined: 10 Jan 2006 Posts: 170 Location: St. Francisville, LA
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Posted: Fri Feb 17, 2006 1:39 am Post subject: Re: Fuel Line Bubbles |
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Hey Ron,
I had a similar experience with my 912/EIS. I'm just throwing this out for you to consider. I had the same problem. Low pressure alarms. Couldn't find the problem. Went looking for vapor lock, etc. Put fire sleeve on lines, rerouted, pull hair out, and on and on.
It ended up being my radio!!!!!
My antenea wire and some of the wires from the EIS sensors shared about 12" in the nose cone. Weird thing is that it never happened on the ground. Not sure why that was. It always happened at the same place, and power settings as I made calls for the pattern. Seperated the wires and no more fuel pressure problems. Boy did I feel dumb.
Just might want to consider that if you run out of ideas on the little bubbles.
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_________________ Thanks too much,
John Bickham
Mark III-C w/ 912UL
St. Francisville, LA
I know many pilots and a few true aviators. There is a distinct difference that I have the greatest respect for. |
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