Over-pressure valve actuation pressure?

[danstrider]

Hi all,
First post despite lurking for years...

Anyone know how much over pressure a typical over-pressure (dump) valve usually takes to actuate? I get that it's a function of the spring and the opening area, but I can't find where anyone who measured the over-pressure.

I know it's a random question. I'm thinking about a constant volume BC like the 1970's Dacor Nautilus Constant Volume System and trying to understand its physics. The CVS seems to be controversial on the forums, but I'm only interested in how it worked. That system has two dump valves both venting outward. Are those the same actuation pressure as a typical bladder over-pressure dump valve?

Thanks!
danstrider

 

[tbone1004]

only a couple psi on standard units. It's highly volatile based on the specific springs though, but not much. You should be able to activate the OPV with your breath and most people can only exhale 1.5-2psi.

the CVS would have had very weak valves to allow it to bleed, likely the same as what is on a standard bcd, maybe lighter. @herman or @Luis H may be able to shed some more light

 

[herman]

no clue on the pressure but it can't be much, it depends on spring ,spring compression and area. Arm dumps on drysuits are the example that comes to my mind. I would set mine lose (it was adjustable) and use it as a constant vent as I ascended.

 

[Luis H]

The Dacor CVS is a hard shell system (somewhat similar to a submarine ballast tanks) with very large valves. I have one that I need to service the regulator.

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.

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.

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.

I will try to find a full description (from Dacor) on how the system is supposed to work. I will try to post it when I have a chance.

 

[NAM001]

only a couple psi on standard units. It's highly volatile based on the specific springs though, but not much. You should be able to activate the OPV with your breath and most people can only exhale 1.5-2psi.

the CVS would have had very weak valves to allow it to bleed, likely the same as what is on a standard bcd, maybe lighter. @herman or @Luis H may be able to shed some more light

tbone. what did they call the bcd lp hose vent that you activated by pulling on the hose. I saw CVS and thought of that.

 

[Luis H]

It was a very interesting design.

The concept of a constant buoyancy at any depth in theory is excellent, but it also has some flaws. But it is a very interesting idea.

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.

 

[Luis H]

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.

 

[tbone1004]

tbone. what did they call the bcd lp hose vent that you activated by pulling on the hose. I saw CVS and thought of that.

pull-dump is the only one that I've heard for it but never really paid attention to them...

 

[NAM001]

pull-dump is the only one that I've heard for it but never really paid attention to them...

thanks i saw cvs and thought cable vent system. now I saw the other posts I understand.

There was a lot of interesting stuff back then to deal with buoyancy. I recall pvc tubes on each side that you could inflate and then take a down angle to vent. bcd really changed things in this regard.

 

[iamrushman]

very interesting concept...thanks for sharing the details.