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RE: [PSUBS-MAILIST] Double O-Ring On A Hatch

Hello Frank,
 
Your right, the elongation lets the flanges seat evenly. I've also seen a double hinging hatch to do the same thing. The thing I didn't like about those types was they felt and sounded sorta clunky. I think I recall that the Nemo sub has a spring type assembly to deal with that. That is what I'm shooting for with my hatches. I would love to see some drawings, specs, and close-up pictures of that part of the Nemos hatch.
 
The Atlantis tourist sub I took a ride on in Kona, Hawaii, had a very small single O-ring in the top flange of the hatch. I've up loaded some pictures I took of it. It also has a very nice locking assembly. Single O-rings have been proven to be safe, I was just considering some ideas. As you likely know ABS specs are always evolving, so just because something isn't in the ABS manual, doesn't mean it won't be in the future or that it's a bad design element.
 
http://www.frappr.com/?a=viewphoto&id=4001713&pid=7561478
 
The Atlantis tourist sub I took the pics of, didn't have a raised conical lower flange, like we see on the Uboat Works subs, Euronaut, and the R300 hatches, to keep small amounts of water from getting in the sub and dripping on you when you open the hatch at the surface. At least that is always what I believed it was for. The Atlantis employee on the sub I was on, had to dry the lower flange surface with a towel before we exited.
 
I suspect that the small O-rings used for hatches are made of a hard rubber or the like, and that they tend to be used on precision machined hatches only, and are best for deep diving subs.  That's just my guess from what I've seen, since I've not been able to get much hard data to compare.  On high end commercial subs I've only seen small cross section O-rings used.  Except the Uboat Worx subs have a larger cross section O-ring.  So in the end I'm still left scratching my head. I guess use what ever you have, or can afford, since size seems to not matter. ; )'
 
I prefer to have the O-ring and it's groove in the upper flange, so I don't walk on it and get dirt on it, and have it seat flat on the lower flange, below the conical lower flange surface like on Carstens hatches. You can also do this sort of thing with Peters type of hatch assembly, using an extra rolled piece of square rod welded to the bottom flange, just inside of the other two rods welded to the top flange for form the O-ring groove, to keep surface water out. This would also make it so if you did have a high pressure leak in the hatch O-ring, the water wouldn't hit you so hard, if you were in the hatch area.
 
The Uboat Worx sub hatches have conical flange surfaces only, with the O-ring and it's groove in the lower flange. The conical flanges will be great to keep the small amount of water out of the sub at the surface, but I don't know how having a O-ring not seated flat will do long term. The more pressure the hatch puts done on it, the O-ring is sweezed down and outward, but at the same time some pressure is coming in the gap between the flanges pushing it the other way. So perhaps it's a great design if it balances out the distortion of the O-ring some.
 

Regards,
Brent Hartwig


From: ShellyDalg@aol.com
Date: Mon, 20 Aug 2007 17:02:20 -0400
Subject: Re: [PSUBS-MAILIST] Double O-Ring On A Hatch
To: personal_submersibles@psubs.org

Brent. I have noticed that the hinge pin on some of the hatches are in a slightly elongated or oval hole so that the pin isn't holding up the hatch when it's closed. Also, some of the guys have hard ''o'' rings, and some have much softer ones.  1/2 inch looks to be the norm. I think if the mating surfaces are machined well enough, you won't get water passing the ring, as the area for water intrusion is VERY small when the hatch is pressed down by external pressure.
The tourist subs I've seen all have one ''O'' ring. Can't argue with what works. Frank D.



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