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12-31-2018, 06:06 PM
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Join Date: Jul 2009
Location: Niceville, Florida
Posts: 434
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Old, soft proseal...
Hi Folks!
I had some fuel weeping around the fuel sender on the right wing tank in my 25 year old RV-4, so I dropped the tank to inspect it and find the source of the leak. Imagine my surprise when I was able to scrape off the proseal around the sender and inspection plate with a fingernail! The rest of the accessible proseal on the tank is hard as is the other wing tank (which I previously removed a couple of years ago to replace the sender and add AOA plumbing forward of the spar).
I suspect a bad batch of sealant was used for the sender and inspection plate when the airplane was first built (or perhaps an non-hardening formulation). After a quarter century and couple of thousand hours, gas simply started to weep from some of the screws...
I will clean up the old sealant and reseal the plate and replace the old style Stewart Warner sender; but I'm curious if anyone has run into something similar and there are any lessons learned that might apply!
Happy New Year,
Vac
__________________
Mike Vaccaro
RV-4 2112
Niceville, Florida
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12-31-2018, 07:01 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Happy New Year !!
Dubbed "reversion" and oddly seems to happen with damp proseal resulting from weeps. It is not unusual, and is frequently claimed to be a result of poorly mixed product. I contacted the 3M lab engineer for polysulfone products and she did some research on their documents and could not find any history of this. With the few cases known, and they were not using 3M product, the investigation ended there.
A local friend in a nearby hangar just had the same "failure" due to a persistent small weep. RV8 ~8 yrs.
DanH has the most complete information, but fits into your description.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
Last edited by BillL : 12-31-2018 at 07:03 PM.
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12-31-2018, 09:13 PM
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Join Date: Jun 2011
Location: Nashua, NH
Posts: 536
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Hi Vac,
I had the same thing happen on my right tank. I took the tank off, cleaned up the area, and was going to replace the sender too. The new Stewart-Warner sender from Vans’ had a different bolt hole pattern, so I reused the old sender. I also used the 3M brand “Proseal” vs what Vans sells, as that brand is the one with issues. I called that company, and after speaking with their “engineer”, I threw it in the trash and went with 3M. No leaks. I also wound up doing the access plate on the same tank, as the sealant was reverting there too. The other tank, done at the same time, same batch, has no issues. Go figure.
__________________
Mike
RV-4 #2750
N654ML
IO-360
WW150C Prop
1018 lbs
Flying
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12-31-2018, 09:51 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by Michael Henning
I also used the 3M brand ?Proseal? vs what Vans sells, as that brand is the one with issues.
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I bit of research will show that the softened sealant issue from extended exposure to leaking fuel has happened with numerous brands of sealant.
Additionally, lack of a leak on the other side doesn't mean the same thing wont occur there as well if a leak ever does start.
The leak doesn't start because of softening sealant.... the sealant softens and degrades because of extended exposure to a leak.
A lot of info available here in the forums with a bit of searching.... it has been discussed extensively in the past.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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01-01-2019, 09:05 AM
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Join Date: Jul 2009
Location: Niceville, Florida
Posts: 434
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Thank You!
All,
Thanks for the quick replies. Key words that worked well for search were "soft proseal."
Another lesson learned thanks to the awesome group resource that VAF is!
Cheers,
Vac
__________________
Mike Vaccaro
RV-4 2112
Niceville, Florida
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01-04-2019, 12:02 PM
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Join Date: Jan 2007
Location: fort myers fl
Posts: 949
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My theory is that it's the blue dye in the fuel. The pro seal is fine with exposure to 100ll, but when the gas evaporates and leaves only the dye, it softens the pro seal. Has anybody that uses only auto fuel has the softening problem.
Bob burns
Rv-4 n82rb
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01-04-2019, 12:28 PM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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Quote:
Originally Posted by n82rb
My theory is that it's the blue dye in the fuel. The pro seal is fine with exposure to 100ll, but when the gas evaporates and leaves only the dye, it softens the pro seal. Has anybody that uses only auto fuel has the softening problem.
Bob burns
Rv-4 n82rb
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Yes. I only use LL when forced to when I travel; E-free premium mogas at home. I've seen softened sealant on my 1991 era tanks.
DanH has linked to research papers showing degradation from gasolines; IIRC, the issue was related to peroxides.
Charlie
(not a chemist; no hotel stays lately)
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