Sealant for polyethylene fuel tank?

On Sat, 3 Mar 2007 08:32:15 +0100, "Rob Turk"
wrote:

"TerryJ" suptjudatcomcastdotnet wrote in message
...
Teflon tape from ACE hardware....

"Rob Turk" wrote in message
. ..
I'm looking for a sealant or kit to seal brass NPT inserts into a
polyethylene tank. This is a Kitfox header tank that has developed a leak
at one of the inserts. I'm probably going to use Mogas that has ethanol
additives. Any hints, tips, thoughts?

Thanks,
Rob

Tried that, but it appears to be eaten by the ethanol additives from Mogas.

Rob

Ethanol will NOT disolve teflon. It is the material of choice for
handling ethanol fuels.

--
Posted via a free Usenet account from http://www.teranews.com

On Sat, 03 Mar 2007 16:21:48 -0500, clare at snyder.on.ca wrote:

On Sat, 3 Mar 2007 08:32:15 +0100, "Rob Turk"
wrote:

"TerryJ" suptjudatcomcastdotnet wrote in message
m...
Teflon tape from ACE hardware....

"Rob Turk" wrote in message
. ..
I'm looking for a sealant or kit to seal brass NPT inserts into a
polyethylene tank. This is a Kitfox header tank that has developed a leak
at one of the inserts. I'm probably going to use Mogas that has ethanol
additives. Any hints, tips, thoughts?

Thanks,
Rob

Tried that, but it appears to be eaten by the ethanol additives from Mogas.

Rob

Ethanol will NOT disolve teflon. It is the material of choice for
handling ethanol fuels.

--
Posted via a free Usenet account from http://www.teranews.com

I like locktite 592 thread sealant for jobs like this. It's a teflon
based pipe dope that doesn't dry out.

clare at snyder.on.ca wrote in message
...
On Sat, 3 Mar 2007 08:36:23 +0100, "Rob Turk"
Can you hog it out to the next size pipe thread and put a reducer
bushing in? Make sure you use a tapered pipe thread and do not
overtighten it. Make sure you use FLEXIBLE line from the tank to the
fuselage. Rigid tubing WILL eventually take the threts out of the poly
tank.


That would get me back to the starting situation; What do I use to seal the
bushing, considering nothing seems to stick to polyethylene..

Rob

On Sat, 3 Mar 2007 22:53:58 +0100, "Rob Turk"
wrote:

clare at snyder.on.ca wrote in message
.. .
On Sat, 3 Mar 2007 08:36:23 +0100, "Rob Turk"
Can you hog it out to the next size pipe thread and put a reducer
bushing in? Make sure you use a tapered pipe thread and do not
overtighten it. Make sure you use FLEXIBLE line from the tank to the
fuselage. Rigid tubing WILL eventually take the threts out of the poly
tank.


That would get me back to the starting situation; What do I use to seal the
bushing, considering nothing seems to stick to polyethylene..

Rob

Buna or "Viton" o-rings as are used on o-ring fittings, face seal
fittings, and flanges the world over. Compress, don't twist. I don't
have a link to the AN series, but SAE (J1926) or BSPP (ISO 1179) work
well with light hydrocarbons and alcohols. My specific experience is
in hydraulics where they are used from vacuum to about 600 bar (9000
psi)

I'm making one REAL BIG ASS U ME thing ... that you can get into the
tank to install a nut. IF not, the expansion plugs mentioned earlier
are a good option.

Note that these fittings are usually steel in my industry, but the AN
versions are also in aluminum; you'll pay more, save weight, but get
the same ports.

Aside; whoever said teflon tape is attacked by gasoline ... I'd like
more information; I've used it many times with no problems of that
sort. My objection with it in a fuel system is that the installation
will leave small particles that plug orifices ... like carburetor
jets.

On Sat, 3 Mar 2007 22:53:58 +0100, "Rob Turk"
wrote:

clare at snyder.on.ca wrote in message
.. .
On Sat, 3 Mar 2007 08:36:23 +0100, "Rob Turk"
Can you hog it out to the next size pipe thread and put a reducer
bushing in? Make sure you use a tapered pipe thread and do not
overtighten it. Make sure you use FLEXIBLE line from the tank to the
fuselage. Rigid tubing WILL eventually take the threts out of the poly
tank.


That would get me back to the starting situation; What do I use to seal the
bushing, considering nothing seems to stick to polyethylene..

Rob


There is a marine product for repairing polyethylene: PolyDura
http://www.marinetex.com/PRODUCT%20P...FAQ%20page.htm

However, the tank must be flame treated for it to adhere!

"Can I use PolyDura to fix my polyethylene gas tank?

We do not recommend flame-treating any project that may be associated
with flammable materials. Flame-treating of items such as fuel tanks,
chemical tanks, pipelines or other flammable containers is not
recommended due to the danger of explosion or fire."

For sealing to polyethylene, Dow 730 fluorosilicone rubber:
http://www.aircraftspruce.com/catalo...ges/dow730.php
http://www.skygeek.com/rtv730-3oz.html

Pretty expensive! Dow 730 is specified in the maintenance manual for
the DeHavilland DHC-8, for tacking down rubber seals in the wing fuel
cell access panels. However, the Dow 730 Product Data Sheet
http://www.dowcorning.com/applicatio...t.aspx?R=406EN
states the following limitations:

• On Teflon®1-coated materials,
polyethylene, polypropylene or
methylmethacrylate (Plexiglas®2);
sealant will not adhere well
• On or near sensitive metals such as
copper, brass, zinc, carbon steel,
galvanized iron or magnesium; these
metals may be corroded, especially
in confined cure conditions, due to
the acetic acid released during the
cure


Or, you could try a visit to your friendly ski repair shop and pick
their brains about hot-air welding of polyethylene ski bases.
http://www.svst.com/page5.html

Harbor Freight offers a hot-air plastic welder, $29.95 :
http://www.harborfreight.com/cpi/cta...emnumber=41592

This sounds like a Proseal-type compound:
http://www.patentstorm.us/patents/6113820-claims.html
Although they package 2 part polysulfide rubber compounds in
polyethylene containers, from my experience it sticks to some of them
pretty well.

Post some feedback on your results, please.

D. Anderson

On Sat, 3 Mar 2007 22:53:58 +0100, "Rob Turk"
wrote:

clare at snyder.on.ca wrote in message
.. .
On Sat, 3 Mar 2007 08:36:23 +0100, "Rob Turk"
Can you hog it out to the next size pipe thread and put a reducer
bushing in? Make sure you use a tapered pipe thread and do not
overtighten it. Make sure you use FLEXIBLE line from the tank to the
fuselage. Rigid tubing WILL eventually take the threts out of the poly
tank.


That would get me back to the starting situation; What do I use to seal the
bushing, considering nothing seems to stick to polyethylene..

Rob

ABSOLUTELY NOTHING. A tapered pipe thread is a "dry seal" thread,
particularly into Poly.


--
Posted via a free Usenet account from http://www.teranews.com

"Rob Turk" wrote

That would get me back to the starting situation; What do I use to seal
the bushing, considering nothing seems to stick to polyethylene..

I think part of the problem here, is that everyone does not know exactly
what you are working with, such as:

Is the location of the fitting in the tank built up at all, or is it like
someone just punched a hole in the tank in a random location, and stuck the
fitting in?

Can you give us a part number, or picture on a site, or at least a
description of the type of fitting that is penetrating the tank that you are
presently using, that is not working?
--
Jim in NC

"Morgans" wrote in message
...

"Rob Turk" wrote

That would get me back to the starting situation; What do I use to seal
the bushing, considering nothing seems to stick to polyethylene..

I think part of the problem here, is that everyone does not know exactly
what you are working with, such as:

Is the location of the fitting in the tank built up at all, or is it like
someone just punched a hole in the tank in a random location, and stuck
the fitting in?

Can you give us a part number, or picture on a site, or at least a
description of the type of fitting that is penetrating the tank that you
are presently using, that is not working?
--
Jim in NC


Here's a link to a Kitfox builders site. It's not my site, but it has good
pictures of the exact same header tank itself:
http://www.scoobysworkshop.com/2005p...tors_small.jpg
http://www.scoobysworkshop.com/2005p...Done_small.jpg

There's no real build up, but the tank has thick enough walls to allow a bit
of thread. There's no openings to allow nuts to go in, meaning that viton
ring approach is practically rules out. The guy that made the pictures has
used some kind of kit or glue to bond the brass inserts into the tank, and
it's this kit that eventually gives way and develops leaks. We got the tank
from a previous owner who was honest enough to tell us about the problem
beforehand and we're trying to solve this in a reliable way.

Rob


Rob

Here's a link to a Kitfox builders site. It's not my site, but it has good
pictures of the exact same header tank itself:
http://www.scoobysworkshop.com/2005p...tors_small.jpg
http://www.scoobysworkshop.com/2005p...Done_small.jpg

There's no real build up, but the tank has thick enough walls to allow a bit
of thread. There's no openings to allow nuts to go in, meaning that viton
ring approach is practically rules out. The guy that made the pictures has
used some kind of kit or glue to bond the brass inserts into the tank, and
it's this kit that eventually gives way and develops leaks. We got the tank
from a previous owner who was honest enough to tell us about the problem
beforehand and we're trying to solve this in a reliable way.

Rob


Rob



OK, bigger pictures at:
http://www.scoobysworkshop.com/2005p...Connectors.jpg
http://www.scoobysworkshop.com/2005p...erTankDone.jpg

Hmmm, looks like no bosses...just threaded into the tank with a sealer
and cinched up with a nut. Is there also a pickup screen on the
inside of the tank, connected to the AN angle fitting? How about a
low point quick drain? Might be a good idea.

You could use a hole saw to cut an access hole that could later be
closed using an expanding, fuel resistant "Thermos style" pressure
cap. Four different sizes at Wicks Aircraft. The 2" TURN-TITE FUEL
CAP looks to be the most secure.
http://www.wicksaircraft.com/catalog...301/index.html
Then you could fish a straight AN bulkhead fitting like this:
http://www.wicksaircraft.com/catalog...955/index.html
with an O-ring on it down a wire and pull it out far enough to get a
bulkhead nut on it.

You should provide some means of inspecting or cleaning out the inside
of the tank anyway.

D.Anderson

"Rob Turk" wrote in message . ..
: clare at snyder.on.ca wrote in message
: ...
: On Sat, 3 Mar 2007 08:36:23 +0100, "Rob Turk"
: Can you hog it out to the next size pipe thread and put a reducer
: bushing in? Make sure you use a tapered pipe thread and do not
: overtighten it. Make sure you use FLEXIBLE line from the tank to the
: fuselage. Rigid tubing WILL eventually take the threts out of the poly
: tank.
:
:
: That would get me back to the starting situation; What do I use to seal the
: bushing, considering nothing seems to stick to polyethylene..
:
: Rob
:
:

The polyurethane itself should act as a sealer. It will cold flow around the threads. You need to be sure all the
threads are smooth to some degree and not over tighten...