My shop heads are coated (at least the ones I could see easily). Must depend on who was doing the proseal work at the QB factory that day.Brantel said:I have looked in a couple more quick build tanks and there is no sealant on the shop heads of any of the rivets. Goes agains what the directions tell you to do if you build them yourself.
I coated mine. In a couple years I will let you know if it helped
Well, our tanks are vented, so the pressure inside should not increase much at all. If the pressure inside the tank is higher than atmospheric pressure, air will escape out the vent line until the pressure equalizes. If the vent is blocked, you would have a problem when you used fuel from that tank, so that condition would be detected.Hard Knox said:Ever leave a metal gas can in the sun. The gases will expand and deform it if it is not vented properly. Could the expansion and contraction of fully fueled tanks cause or contribute through contraction and expansion of these rivet points and allow gasses to escape through a few rivets?
gorbak said:I can't imagine there is a common thread when there are so many variables. A stab in the dark would be foreign substances trapped under the rivet heads and too much paint applied causing solvent pop around the rivet heads.
Pat Garboden
Captain Avgas said:Pat, of course you can get general coating problems, including trapped solvents, if the preparation and paint job on a plane are not done properly.
HOWEVER, what we are talking about here is specifically blistering on rivets AT THE FUEL TANK ONLY and where they do not appear anywhere else on the entire plane. This has proven to be a very common phenomenon.
The ONLY logical conclusion one can draw from this particular phenomenon is that the blistering is caused by fuel or fuel vapour weeping through rivet holes.
To date, no-one has reported a case of this occurring on fuel tanks when their shop heads (inside the tank) have been fully encapsulated.
I again request anyone who has experienced blistering on tanks with fully encapsulated shop-head rivets to step forward. If no-one comes forward I think we can conclude what the problem is.
David-aviator said:The few shop heads I can see looking through the fuel cap hole with a flash light are not covered with proseal - QB tanks.
Bob: I hope you are right, and it is that simple but I don't think so. I have built an RV6A and an RV7A both slow build so that makes 4 tanks. I built all four of them the same way and I completed covered the shop heads inside the tanks. ""They all passed the pressure test. The only difference was the way I painted them. The 6A was vinel wash, epoxy primer and Jet glow urethane. No problem. The 7A was Mar hyde self etching primer and jet glow. I took a short cut and paid for it. Blisters on the tank rivets. As I said I hope you are right and it is just vaper leaking out.Captain Avgas said:I asked Vans if they have a manufacturing specification on the QB tanks requiring full proseal encapsulation of the rivet shop heads. No such spec exists. They only require that the QB tanks pass a pressure test.
So we now know why some QB tanks have full proseal encapsulation of the shop heads....and others do not. It's left up to the subcontractor who obviously changes his mind from time to time, depending on the success he's having with the pressure test.
To date, not one builder with either QB or Slo-build tanks that has rivet shop heads fully encapsulated in proseal has reported tank blisters. EVERY case of blisters reported to date DOES NOT have encapsulated shop heads.
So it is obvious what the problem is. With movement over time, some tank rivets weep microscopic quantities of fuel (or fuel vapour). Most don't, but some do. The fuel eventually causes delamination of the primer adjacent to the rivet.
Completely encapsulating the rivet shop head (inside the tank) eliminates the problem.
Captain Avgas said:To date, not one builder with either QB or Slo-build tanks that has rivet shop heads fully encapsulated in proseal has reported tank blisters. EVERY case of blisters reported to date DOES NOT have encapsulated shop heads.
casper said:Bob: I hope you are right, and it is that simple but I don't think so. I have built an RV6A and an RV7A both slow build so that makes 4 tanks. I built all four of them the same way and I completed covered the shop heads inside the tanks. ""They all passed the pressure test. The only difference was the way I painted them. The 6A was vinel wash, epoxy primer and Jet glow urethane. No problem. The 7A was Mar hyde self etching primer and jet glow. I took a short cut and paid for it. Blisters on the tank rivets. As I said I hope you are right and it is just vaper leaking out.
My theory is well known....so naturally I'd be interested to know if the shop heads of the rivets were properly encapsulated. So far, I've seen no real evidence....none so far....that would cause me to abandon my theory about the root cause of this problem. Since in your case the blistering seems to occur along the back baffle, removal of the tank from the wing would very quickly confirm if the rivets were encapsulated or not. If they are encapsulated...and you provide us with detail photos of acceptable encapsulation......I would then resume my place among all others who have no real idea as to what is causing the problem. If however, in your case the shop heads of the rivets are not properly encapsulated, I believe you (unlike many others) can anticipate a relatively easy fix.I've noticed through all of these threads that no one has posted a picture. Whatever the cause, I just don't think it's a pressure thing.
Oops, let me try again.....
http://img233.imageshack.us/img233/6537/dscf0765mi5.jpg
While considering the cost of building new fuel tanks, I noticed Van's no longer sells pro seal.
Now that's interesting, maybe the stuff isn't perfect after all.
The picture still shows Flamemaster, producer of the original Proseal right? Aren't they the same even though the catalog lists it by mil-spec instead of Proseal? the B- designation If I recall, pertains to the working time, i.e. B-2, two hours?
Ya'll remember that one when you get tempted to think precise ratio control isn't necessary...mixing epoxy, proseal, polyester, whatever.
Not quite the right observation from our data, which is "do a really good job mixing 2-part systems". Within reasonable limits, precise ratio control effects pot life, not mix (final product) quality. However, if too little catalyst is applied there may be insufficient crosslink and the material may never achieve final quality. Too much catalyst usually just reduces application time.
Dave,Fuel as a factor is also ruled out because there is no fuel at the aft flange, the rivets are outside the tank and that's where the blisters showed up first......
I amy have missed it, but has anyone identified the exact sealant brand and PN applied at the QB facility? Can't chase Bill's idea if we don't know the chemistry. Seems like we need a MSDS at a minimum.
Bill, very good point about mixing. I'm guessing the QB folks use a cartridge system. How well do cartridge systems really mix?