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  #11  
Old 02-03-2015, 01:06 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by BillL View Post

Depending on the answer -the question is - will ALL tanks eventually have leaks at the top where the fuel does not touch when parked?
No, or thousands of RV's would now be leaking (and that is not the case).

If there is a leak or seep where sealant is always being exposed to evaporating fuel, the sealant will become soft.

If you want to know the chemistry explanation you will have to contact the sealant manufacturer, but they will tell you the same thing
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  #12  
Old 02-03-2015, 01:37 PM
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ArVeeNiner ArVeeNiner is offline
 
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Thanks everybody. It seems like this is a normal phenomenon and maybe not the result of an improper mix ratio. Who knew?

I'm in the middle of cleaning up all the soft stuff and fuel and should have ample amounts of new sealant in place in the interior of the tank in the next day or two. I'll also lop some more on externally just for good measure.

Thanks again!
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  #13  
Old 02-03-2015, 01:58 PM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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So I presume the takeaway here is : See a leak? Drop everything and fix the leak?
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  #14  
Old 02-03-2015, 02:57 PM
RVDan RVDan is offline
 
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There are a lot of variants of "Proseal". At least 3 different manufacturers and 2 or 3 varieties for each manufacturer. What stuff are you using on the fuel tanks?
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  #15  
Old 02-03-2015, 04:32 PM
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Quote:
Originally Posted by BillL View Post
What are the bench/lab validation results for dipping in fuel, what are the quantified acceptable parameters for long life?
There are no standards specific to 100LL exposure. All the standard tests use JRF:

http://standards.sae.org/air4275/



Quote:
Originally Posted by rvbuilder2002 View Post
If you want to know the chemistry explanation you will have to contact the sealant manufacturer, but they will tell you the same thing
Oddly enough, a few years ago my contact at Flamemaster said he knew nothing about it. Mind getting the full explanation for us?
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  #16  
Old 02-03-2015, 05:28 PM
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Quote:
Originally Posted by DanH View Post
Oddly enough, a few years ago my contact at Flamemaster said he knew nothing about it. Mind getting the full explanation for us?
Dan, I have not ever personally talked with anyone at Flame Master about this, but in response to people inquiring with tech support regarding this issue, at least someone at Van's has.
Since I have seen it numerous times (once a very mild case on my own airplane), and the word that someone at Flame Master acknowledged it can happen, that has always been enough information for me.

They way I look at it... I don't need to know why.... I just need to know to always be inspecting for fuel leakage, and then fix it as soon as it is detected.
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  #17  
Old 02-03-2015, 06:18 PM
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Quote:
Originally Posted by rvbuilder2002 View Post
Dan, I have not ever personally talked with anyone at Flame Master about this...
Sure, sure, but you know how it is...sometimes a vendor will honor a request from an OEM when the rest of us poor schlubbs get blown off. Yet, the schlubbs, being dedicated to education and recreation like we are, would really like to know the chemistry. You could ask 'em to write it down for us, and then post it here. That would be great.

BTW, oxidation is a maybe, but I soaked a cured sealant sample in 3% hydrogen peroxide nearly 4 years without softening. It did eat the metal can.

And I recently examined a softened polysulfide sealant sample taken from inside a tank. It wasn't fully reverted (more like not very sticky week-old chewing gum, or old-fashioned window glass glazing putty), but certainly not normal-as-cured. The owner removed the rivets and easily peeled the skin off the ribs. Samples from the top of the tank (vapor/splash exposure) and the bottom of the tank (submerged exposure) were similar. Samples of the same sealant from outside the tank (zero fuel contact) were solid/normal. Built circa 2005, sealant brand unknown; checking now.

Postscript: Sealant was Chem Seal (Flamemaster) 3204-B....same stuff common to RVs.
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  #18  
Old 02-03-2015, 06:37 PM
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Maybe it just a coincidence, but everytime I've seen this it was with the flamemaster stuff.
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  #19  
Old 02-03-2015, 08:46 PM
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Quote:
Originally Posted by Walt View Post
Maybe it just a coincidence, but everytime I've seen this it was with the flamemaster stuff.
So taking Walt's advice, this is what I just purchased to do the tank on my -12. http://www.skygeek.com/prc-desoto-ps...lant-pint.html
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  #20  
Old 02-04-2015, 06:38 AM
RVDan RVDan is offline
 
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Quote:
Originally Posted by Walt View Post
Maybe it just a coincidence, but everytime I've seen this it was with the flamemaster stuff.
So this was my point in asking what people were using. The company "Proseal" hasn't existed for years, it was purchased by Courtaulds, then Courtaulds (former PRC) was purchased by Akzo then PPG. or at least something like that. PPG now has the products of both former companies. PS890 is the common and original "Proseal" product that meets Mil-S-8802. PR1422 and PR1440 are of the old PRC products for fuel tank sealant, but there are many others. This could be a product specific problem.

I have some work experience (more than 30 yrs) with PS890, PR1422 and PR1440 and never heard of this problem with avgas. Problems from inproper mixing and curing in an environment that was to cold, yes, but not properly mixed and cured.
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