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Wouldn't the
hatch be metal to metal and the pressure coming in at the hatch/seat division
make the o ring try to extruded into the sub. The pressure that the o ring
would extrude would be very high, higher than the collapse pressure of the sub I
would think.
Brian
I worked up three more drawings
to show what I was thinking a O-ring in a coved gland or square gland with
silicone or urethane filling the square corners of the gland, would look like
being under great pressure. Since I think there would be far more pressure
coming down on the O-ring from the hydrostatic pressure on the hatch's outer
surface then would be coming in from the space between the hatch flange and
seat. Also I would expect that the more exterior hydrostatic pressure is
applied to the hatch that it would further help seal the O-ring against the
seating surface, keeping it from extruding to the low pressure side of the
seal. Any
thoughts?
http://www.frappr.com/?a=viewphoto&id=4001713&pid=9275457
Regards,
Brent
Hartwig
From: brenthartwig@hotmail.com
To:
personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Bottomed Out
Hatch Flange O-ring Failure
Date: Sat, 2 Feb 2008 15:37:06 -0800
I've been thinking about this for some time
now, and thought it was time to talk about it. There has been a fair bit of
discussion on O-ring failure in a hatch, by means of extrusion. I don't
think this would be the mode of failure for a hatch O-ring, and here is why.
When the hatch is shut and under water, the exposed surface area on the
O-ring between the two metal mating surfaces is vastly smaller then the
surface area on the top of the whole hatch pushing down on it. This means
that if the pressure is to great for the O-ring, the hatch mating surfaces
will bottom out and then the water will just start to flow past the O-ring
without extruding it. Also if the hatch bottoms out there will be no place
for the O-ring to extrude into. At this point I think the O-ring would just
rather let the water pass between it and the flat flange mating surface,
rather then extrude. Any thoughts?
I made up a model to better
show what I'm thinking the O-ring would look like when fully compressed into
it's gland by a bottomed out hatch flange.
http://www.frappr.com/?a=viewphoto&id=4001713&pid=9115314
Here
is a really great link I found today showing a lot more modes of O-ring
failure then I'd seen any place else.
http://www.allorings.com/failure.htm
Not to long ago Frank D. asked about whether he
should cut a coved or square O-ring groove in his hatch, and I don't
remember if any one answered him? I would think the cove would make
for less room for a O-ring to deform into to help keep the metal hatch
surfaces from bottoming out. While watching the Nova show on the Alicia sub
called "Underwater Dream Machine", I noticed that they put a lot of silicone
type sealant in the O-ring groove that is in the large unboltable flange,
that keeps the two large steel pressure hull sections together. I'm
guessing they did this to fill the extra space of a square type O-ring
groove, that the O-ring doesn't fill when in a non compressed state. So
there will be more space between the flanges at depth, to keep them from
bottoming out. Any thoughts, or should I add more O2 to my snow
cave?
Here are two pictures showing snow through the windows of my
house. One shows snow up against a window in the the spa room, and the other
shows that the snow outside my shop window is completely blocking the view
out the window. So when I say snow cave, I mean it. This is not normal for
around
here.
http://www.frappr.com/?a=viewphoto&id=4001713&pid=9115443
Regards,
Brent
Hartwig
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