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Dennis.Kirby(at)kirtland.
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 Posted: Mon Mar 09, 2009 8:03 am Post subject: Atmospheric Pressure |
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Classification: UNCLASSIFIED
Kolb Friends –
Here’s an interesting phenomenon I observed this weekend while working on my Mark-3:
I put 10 gallons fuel into my gas tanks, but did not balance it evenly. After fueling, there were 7 gallons of gas in one tank, and 3 in the other. A fuel imbalance like this never bothers me, as it always balances out when I fly – both tanks tee into a single fuel line that goes to the engine. Usually, within a few minutes after taking off and with the engine drawing fuel from the tanks, the tanks settle to a level where they are exactly even.
But yesterday, after fueling, I did not fly; I spent the afternoon working on my Kolb. To my surprise, both tanks were at EXACTLY the same level, two hours after I had added the gas. Apparently, the normal atmospheric pressure was enough to bubble the fuel thru the tee, with the tanks balancing themselves naturally.
I had never seen this happen before. Kinda cool, as I did not think the natural ambient air pressure was enough to do this. Always something new to learn with this airplane!
Dennis Kirby
Mark-3, N93DK, in
Cedar Crest, NM
Classification: UNCLASSIFIED
[quote][b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Mon Mar 09, 2009 8:41 am Post subject: Atmospheric Pressure |
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Dennis:
Reckon it was gravity that equalized the level?
john h
mkIII
[quote]
----- But yesterday, after fueling, I did not fly; I spent the afternoon working on my Kolb. To my surprise, both tanks were at EXACTLY the same level, two hours after I had added the gas. Apparently, the normal atmospheric pressure was enough to bubble the fuel thru the tee, with the tanks balancing themselves naturally.
I had never seen this happen before. Kinda cool, as I did not think the natural ambient air pressure was enough to do this. Always something new to learn with this airplane!
Dennis Kirby
[b]
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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Jimmy Young
Joined: 24 Nov 2007
Posts: 182
Location: Missouri City, TX
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| Posted: Mon Mar 09, 2009 9:20 am Post subject: Re: Atmospheric Pressure |
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Dennis,
The way I see it, pretty sure the tanks should balance out since they are connected via the fuel lines. Bottom draw tanks should level out due to a fluid seeking it's own level, top draw tanks due to the higher tank siphoning into the lower one.
A top drawing pair of tanks may not balance out when the situation exists where the fuel has left the fuel line for some reason, such as when an engine has not run it a while and the fuel drains back to the tanks, or when you have opened a line for some reason during maintenance. In that case, once you prime the engine and start her up, they will level out.
My tanks always balance out whether the engine is on or not, & mine draw from the top, except when I have opened the lines.
Jimmy Y
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Jimmy Young
Missouri City, TX
Kolb FS II/HKS 700 |
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Jimmy Young
Joined: 24 Nov 2007
Posts: 182
Location: Missouri City, TX
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| Posted: Mon Mar 09, 2009 10:53 am Post subject: Atmospheric Pressure |
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>>Reckon it was gravity that equalized the level?<<
Yeh, that's it. Good example of the KISS rule.
Jimmy Y
[quote][b]
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Jimmy Young
Missouri City, TX
Kolb FS II/HKS 700 |
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Mon Mar 09, 2009 11:34 am Post subject: Atmospheric Pressure |
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If it was my airplane and I had two fuel tanks, I'd be pulling fuel from the bottom instead of the top. Don't think I would have a leveling problem either. 
john h
mkIII
[quote]
>>Reckon it was gravity that equalized the level?<<
Yeh, that's it. Good example of the KISS rule.
Jimmy Y
[b]
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Mon Mar 09, 2009 12:03 pm Post subject: Re: Atmospheric Pressure |
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The stock MK III twin tanks that feed from the top will self equalize over time, either on the ground or in flight... It does so by gravity and Siphoning action. A siphon does not care if its feeding into another tank beside or below the full tank, it will siphon until the pressure, or levels of the gasoline are equal. Its a bit slow, but it works !
Mike
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"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
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slyck(at)frontiernet.net
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| Posted: Mon Mar 09, 2009 4:40 pm Post subject: Atmospheric Pressure |
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Mike, I respectfully disagree. I have top suckers and they will stay
at the same unequal level for years.
-at least until they evaporate.
I have them valved for either or both usage but it makes no diff how
they are valved while out of use.
BB
On 9, Mar 2009, at 4:03 PM, JetPilot wrote:
| Quote: |
The stock MK III twin tanks that feed from the top will self
equalize over time, either on the ground or in flight... It does
so by gravity and Siphoning action. A siphon does not care if its
feeding into another tank beside or below the full tank, it will
siphon until the pressure, or levels of the gasoline are equal.
Its a bit slow, but it works !
Mike
--------
"NO FEAR" - If you have no fear you did not go as fast
as you could have !!!
Kolb MK-III Xtra, 912-S
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p 33928#233928
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Dana
Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA
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| Posted: Mon Mar 09, 2009 5:12 pm Post subject: Atmospheric Pressure |
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At 08:37 PM 3/9/2009, robert bean wrote:
| Quote: |
Mike, I respectfully disagree. I have top suckers and they will stay
at the same unequal level for years.
-at least until they evaporate.
I have them valved for either or both usage but it makes no diff how
they are valved while out of use.
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Tanks plumbed together below the fluid level will always equalize. Tanks
plumbed together above the fluid level will equalize if and only if there's
no air in the line... just like siphoning gas out of a car, you have to
suck all the air out and get the tube full to below the level in the tank,
then it will keep flowing.
-Dana
--
Lie ? Me ? Never! No, no, no, the truth is far too much fun!
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jbhart(at)onlyinternet.ne
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| Posted: Mon Mar 09, 2009 6:17 pm Post subject: Atmospheric Pressure |
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At 08:37 PM 3/9/09 -0400, you wrote:
| Quote: |
Mike, I respectfully disagree. I have top suckers and they will stay
at the same unequal level for years.
-at least until they evaporate.
I have them valved for either or both usage but it makes no diff how
they are valved while out of use.
BB
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Bob,
If you vent both tanks to the atmosphere, and set your valve to connect both
tanks, it should make an inverted siphon and the tanks will equalize. The
only reason that they would not do so is if the siphon is broken, such as,
fuel back feeding from the carburetor and/or the fuel pump due to a small
air leak somewhere in the system. May be the valve is the culprit. This will
cause a vapor lock in the inverted siphon and hence unequal levels.
You may want to check it out.
It is warming here so that I could fly, but the wind has been fierce.
Knocked some shingles off the roof.
Jack B. Hart FF004
Winchester, IN
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