|
Hi Alec, I consider that a valid point. My
thinking is that if one chooses the right durameter harness of Sekaflex or the
like, thickness of urethane under the upper sealing rings, and the right size
and spacing of upper sealing rods that the design perhaps could handle the
general operating depth of the K-250, K-350 and perhaps higher. 111 psi
for the K-250, being pressed mostly down on the hatch, then that load being
transferred to the urethane might not damage the
harder urethanes.
For hatches that go metal to metal under a certain
amount of pressure. Once that happens, no more addition pressure from that point
is being added to the O-ring to seal it further as I understand it. Of course if
the parts are designed properly, you shouldn't have a issue with it staying
sealed unless you go much much much deeper then they are designed for.
My original hatch has a good size soft O-ring in a
square gland on the hatch. It might all fit in the gland and allow the
hatch and hatch land to got metal to metal, if you went way to deep, and nothing
else on the sub failed. But for some larger cross section
O-rings, as well as ones set in a curved gland that gives no place for the
O-ring to deform into, in a extreme test, I think it would look like
this.
Regards,
Szybowski
From: Smyth, Alec
Sent: Friday, September 04, 2009 5:57 AM
Subject: RE: [PSUBS-MAILIST] No Machining Hatch Sealing
Concept The reason an O ring seals so well is that, so long as there
is an initial seal, increasing pressure expands the width of the O ring thus
increasing it's sealing ability. In other words, the higher the pressure the
better it seals. In this case the two SS rings that sit on the
Sikaflex won't expand. The Sikaflex seat will deform under pressure, but in
the opposite way you want it to. Pressure will tend to expand the Sikaflex
to deepen the recess under the SS rings and tunnel under them.
I'm not saying it wouldn't work at all. I think it
would, but only at low pressures.
At least that's my take. Very nice renderings
though!
Alec
The contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it. From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent
Hartwig
Sent: Friday, September 04, 2009 7:14 AM Subject: [PSUBS-MAILIST] No Machining Hatch Sealing Concept This is an idea I've been wanting to make some CAD
models and drawings of for some time now. We have this big oval or rectangle
steel plate doors for the hyperbaric chambers, and it's expensive to machine the
doors and seating flanges flat, plus cut the O-ring groove. Even then the welded
in door frame can and usually warps some. Once welded in the door frame is very
hard to machine. The concept shown in the below pictures and
drawings, is showing a K-350 type hatch and hatch land, that have two rolled
1/4" SS rod rings, that are TIG welded onto the hatch flange, and two on the
hatch land. The two on the hatch land are to form a dam for Sekaflex, that
you caulk in there and level off. Then to allow the upper SS rings to seat
down into the Sekaflex enough to take up any warp in both flanges and not stick
to the Sekaflex while it is curing, you apply mold release to the SS rings, and
then spray them with PVA mold release agent and let that dry. Then before
the Sekaflex is caulked into the lower rings, you lower the hatch and figure out
what spacers you need to keep if from going down to far into the urethane. Then
add the Sekaflex of the type of hardness you want, and lower the hatch, which is
attached at the hinge to keep every thing lined up, and set the hatch down on
your taped or clamped on spacers, and let it cure.
One could use just one upper SS sealing ring as you
can see in the drawing of a large WWII ballast tank flapper valve. But I
like the primary and secondary sealing means, and it evens out the stresses
more.
" Stand still.
The trees ahead and bush beside you are not lost." ~ Albert
Einstein
Regards Szybowski |