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Hi Guys. Cliff brings up a good point. The use of thread-o-lets is an
accepted practice on pressure vessels of all types, and the forged ones can
withstand lots of pressure.
The '' disk'' method also has some important advantages if you have plans
to change/modify/add to a particular area. This ''disk'' area MAY have a greater
risk of leakage past an ''O'' ring but definitely would make it easier to
change.
Overall, I think the thread-o-lets are strongest, but also the hardest to
change.
I have chosen a compromise solution by using the nipples. Maybe not quite
as strong as the female thread-o-lets back to back on the hull, but the nipples
have some advantages.
A schedule 80 nipple is much stronger than the surrounding hull, so I don't
see strength as a problem. A male nipple can be repaired/re-threaded easily if
some damage were to occur. Total replacement is a little harder than the disk
method, but less trouble than the Thread-o-let method. If you are making an
electrical through-hull, the nipple method is more leak proof than either the
disk or thread-o-let method. The nipple is filled with epoxy, and I can't see
how that would leak. I have a rough sketch on frappr showing the basic
components.
As for Dean's use of epoxy on the threads, I'm not sure that's a good
idea.( sorry Dean ) That may cause some problems and JB isn't really
designed for that application so I doubt there is any reliable data on this use.
There are several good, tried and true, well documented marine grade pipe dopes
available that would work better. Epoxy may make it difficult to change out a
valve or fitting, and because it has a different rate of expansion/contraction
than the associated parts, it may fail. A sealing compound should remain
flexible and also act as a lubricant, especially when you have two or more types
of material joined with a sealant between them.
One more thing to consider, stainless threads on stainless threads can
''gall'' or basically get really screwed up and a ''stainless specific'' sealer
should be used in this case. I am using brass ball valves on the inside because
they are less expensive, but more importantly, because the brass threads seal
better against the stainless nipples than either stainless or steel valves. The
softer brass material forms to the corresponding threads of the nipple, making a
very tight seal, and the two materials when joined, don't ''bond'' or get stuck.
Replacement or ''snugging down'' is easy. If a little seepage occurs on the
inside while submerged, a little more torque with a wrench should stop it, at
least enough to get back to the surface for a more complete investigation and
repair. Frank D. Start the year off right. Easy ways to stay in shape in the new year. |