iamrushman
Contributor
very interesting concept...thanks for sharing the details.
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Got it. This is a great summary.The idea is that the diver can set the amount of air and water volume in the hard shell and the system will maintain the same volume of air at any depth. Air is vented and added as necessary to maintain the same volume, without exceeding too high of a pressure differential between the inside of the hard shell and outside ambient pressure.
A normal bladder BC won't vent until it is fully inflated, so I can't figure the over-pressure feature is commonly used. Certainly, the thick plastic shell should tolerate more pressure than a bladder.The hard shell could probably tolerate a little bit higher positive pressure differential than a soft BC, therefore the vent might be a bit stiffer.
I get that the dedicated regulator would equalize the pressure inside the shell. And I get that this is similar to the physics of a second stage. It's probably doable to convert a cheap second stage for this purpose, if equalizing this way is neccesary.Negative pressure differential was equalized (compensated) by a dedicated regulator and it looks like anything overs a few inches of Water Column would actuated, just like any low end octopus type regulator.
The only big issue I have with the implementation is how big it is. I think it has a lift capacity of about 40 pounds. That means that if you are properly weighted, you have to actually fill it with about 40 pounds of water. You have to empty all the water as you try to get out of the water.
I transcribed the 1977 Skin Diver article, so at least you can read the text more easily!In the June 1977 Skin Diver magazine there was a good article describing the Nautilus. I have a very poor copy of the article. I would like to get a good copy of the article.
Ha! I of course had to click on the patent doc to at least take a glance, and one of the inventor names sounded a bit familiar. Sure enough, Jack Bohmrich was at SeaSoft for a while as VP of Sales. LinkedIn says he is still there, but a few years ago I was told he had left. Maybe he is back again, but it has been a while since I have needed to order anything there so I wouldn't know. So I suppose if you really want to speak with the designer with any questions, you have a route for tracking him down.Thanks for all your replies, and thanks Luis for posting the articles on the CVS and for posting several descriptions of common issues. Sounds like the CVS widget worked, but was just finicky or unreliable or too bulky for its value. Luis, what other "several flaws" did it have in operation with regard to the physics?
Got it. This is a great summary.
A normal bladder BC won't vent until it is fully inflated, so I can't figure the over-pressure feature is commonly used. Certainly, the thick plastic shell should tolerate more pressure than a bladder.
I bought a DGX over-pressure / dump valve to measure how much pressure it takes to actuate. These are fairly stiff springs. Matching herman's comment about adjusting them for a constant bleed to control ascent with a drysuit, these valves can be unscrewed some to change the spring preload, so decreasing the activation pressure.
I also bought a DGX power inflator hose with pull-to-dump. This mushroom valve looks to vent at a lower differential pressure, but they also have a non-dump solid elbow.
I get that the dedicated regulator would equalize the pressure inside the shell. And I get that this is similar to the physics of a second stage. It's probably doable to convert a cheap second stage for this purpose, if equalizing this way is neccesary.
At risk of a stupid question, what if another over-pressure valve was mounted backwards to the shell instead of using the equalizing air regulator? The shell's pressure would still equalize occasionally, but this would change the air/water ratio and "reset" the neutral trim depth. If this reset occurred when outside of say a ~10ft band, then you'd simply swim down and the simple valve would match your new desired trim depth, no? I don't yet understand what value there is in using air to equalize the internal shell pressure.
The 1977 article mentions about 60lb positive on the surface, giving roughly 7.5gal of displacement. Another article mentions most divers should aim for 2/3 to 3/4 full of water for neutral trim ... this means to me only roughly 2gal of air is needed, meaning the CVS is multiple times larger than it needs to be. If it were roughly the same size as a typical tank, and strapped into a dual tank configuration, would that help with the bulk? Also, how long does it take to drain the ~40lb of water out of the shell?
I transcribed the 1977 Skin Diver article, so at least you can read the text more easily!
The Dacor CVS patent is also very helpful.
Pretty much committed myself to building something at this point, so really want to understand what pieces I'm missing...
danstrider