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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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