Re: [PSUBS-MAILIST] Coved O-ring Groove

Jim,

Go to http://apps.parker.com/ead/cm2.asp?cmid=2973 and download the Parker inPHorm O-ring software for free. This is the software that I used to design the gland I used for my boat hatch. The program will give you the exact dimensions of the o-ring seat including the taper angle. It will also give the hardness of the o-ring required given the pressures you are trying to seal against.

Cliff

----- Original Message ----
From: Jim Kocourek <kocpnt@tds.net>
To: personal_submersibles@psubs.org
Sent: Friday, February 22, 2008 6:10:23 AM
Subject: Re: [PSUBS-MAILIST] Coved O-ring Groove

Hi Brent,

I am just preparing to have my hatch oring groove machined. I am planning on the rectangular cross section as shown in your drawing with a slight coved outer side.

I am told that there is this type of layout on K-Boats. In either case, does anyone have or have access to exact dimensions for this type of groove. I am planning on using a 3/8 inch cross section O-ring.

Best Regards,

Jim Kocourek

----- Original Message -----

From: Brent Hartwig

To: personal_submersibles@psubs.org

Sent: Thursday, February 21, 2008 11:36 PM

Subject: RE: [PSUBS-MAILIST] Coved O-ring Groove

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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