Mechanical BC's - is it possible?

[fisherdvm]

You could do away with the mechanical seal issues by adopting a very simple liquid system like those used on the ocean gliders.

In such a system you have a vessel filled with liquid and a small pump. Liquid can then be pumped to fill external, otherwise collapsed, tubing. Thereby, increasing or decreasing the mass of the vessel. It could be powered and controlled either manually or electronically.

Could be a very entertaining project to work on in your spare time. Please, keep us informed of your progress.

Great idea, hydraulics seems to work better than pneumatics, right? Simply using water pumped to control air pressurized to 3 ATM in a very durable plastic elastic jacket inside your rigid cylinder. A manual water pump could be used. As long as you are above 100 ft of water, the system will maintain constant boyancy.

 

[fweber]

The gliders I've taken this idea from have travelled as deep as 4,000 ft, I believe. So 100 should be no problem. I think that if you pump "against" the external pressure of the ocean you will see that you are not limited by the internal pressure, as long as the pressurized head space is of sufficient volume to fill an otherwise empty vessel. Your challenge will be shaping your pressure vessel to achieve the desired displacement without being overly cumbersome. 2.2 lb/ltr leads to needing 15 ltrs to equal a typical 30-35 lb recreational bc. That's a reasonably large cylinder.

Best of luck, but keep working on it,

 

[Humble older aquaman]

It's probably about the money. Has many have stated, devices like this exist. In the commercial diving world there's a lift system where the diver connects the device to the object to be lifted, hits a button, the gadget picks it up a little, the diver checks the rigging, if happy presses a button again, and the gadget takes object to surface at a rate it was programed for. Needless to say it's a pricey gadget.

It's probably a matter of time, but I believe the future will bring a gadget to regulate BC functions. Aqua Lung/Apex has a computer chip in first stage now...most of us dive with computers...a device to auto pilot our depth is only a matter of time and the all important dollar.

The big question is, is it improvement?

Hoa!

 

[O2BBubbleFree]

A couple of years ago I had the opportunity to play around with one of these. Unfortunately it didn't meet our needs.

However, it uses a mechanism that I believe is similar to the ROV mechanism mentioned above. It's a simple electric ram working against a sealed air chamber. When the ram compresses the air in the chamber, it sinks. When the ram expands the air, it rises. No venting, no pumping.

This particular device just dives and surfaces, but precision depth control would be possible with precision ram control.

I don't think you would have to worry about electronic sensors and control. Just have 'up' and 'down' buttons. When the diver wants to rise, he holds the 'up' button 'til he reaches the desired depth. Opposite to sink.

However, you would probably need to make it so that the rise and dive rates are variable. Maybe pressure sensitive switches? So that the harder the diver pushes on the 'up' button, the faster the piston moves, and the faster the ascent rate?

Oh, and here is a link that discussed this same topic two years ago (give or take 10 days).

 

[Luis H]

I have been looking at using rigid ballast tanks to maintain perfect neutral buoyancy for a wile. With today’s integrated computers that read depth and tank pressure it is very technically feasible to have an automatic ballast system that would compensate for wetsuit compression and the tank weight change due to air consumption.

With such a device I would be able to dive like I did as a kid in the Caribbean. With minimal thermal protection, I was always basically neutral and I swam in a true three dimensional world (no BC ever needed).

Back in the late 70’s Dacor had the Nautilus CVS (Constant Volume System). I own one. I bought recently to experiment with it. It is a rigid ballast tank device that you adjusted the amount of water and air in it to be neutral and a regulator added air as you went down and vented as you went up. Interesting idea but it had no means of compensating for wetsuit compression or tank weight change.

The concept of an automatic compensator is very sound and I have been working on some of the details (I am mechanical and an electrical engineer), but the cost and complexity may keep it from ever been produced.

On of my concepts would pump water in and out of the rigid ballast tanks. The computer would be pre-programmed for the compression of different wet suit thickness and types. In addition it would have data for different tank sizes. Sounds complicated doesn’t it. It really isn’t.


Next summer I may test a very simple rigid ballast system using capped PVC pipes that I would manually flood when I am returning to shallow water and my tank is closer to empty. This will allow me to carry less compressible air in my bladder BC at the beginning of my dive. Therefore, less buoyancy fluctuation for our shallow dives here in Maine with a 7 mm wetsuit (14 mm around my torso).

 

[Marek K]

I still have the greatest confidence in the mission Dave.

*sigh* I wonder how many folks don't understand the reference...

 

[Thalassamania]

Fish swim bladders are filled with oxygen, which is carried there by hemoglobin. When the blood surrounding the bladder becomes slightly acidic, it releases oxygen into the bladder. If the blood pH goes up the oxygen is reabsorbed. The hemoglobin of most other animals is also sensitive to pH, but to a much less degree.

 

[Thalassamania]

Great idea, hydraulics seems to work better than pneumatics, right? Simply using water pumped to control air pressurized to 3 ATM in a very durable plastic elastic jacket inside your rigid cylinder. A manual water pump could be used. As long as you are above 100 ft of water, the system will maintain constant boyancy.

What’s used in the ROVs is simple mechanics, aluminum disk with an o-ring sliding in a tube on a worm gear.

A couple of years ago I had the opportunity to play around with one of these. Unfortunately it didn't meet our needs.

However, it uses a mechanism that I believe is similar to the ROV mechanism mentioned above. It's a simple electric ram working against a sealed air chamber. When the ram compresses the air in the chamber, it sinks. When the ram expands the air, it rises. No venting, no pumping.

This particular device just dives and surfaces, but precision depth control would be possible with precision ram control.

I don't think you would have to worry about electronic sensors and control. Just have 'up' and 'down' buttons. When the diver wants to rise, he holds the 'up' button 'til he reaches the desired depth. Opposite to sink.

However, you would probably need to make it so that the rise and dive rates are variable. Maybe pressure sensitive switches? So that the harder the diver pushes on the 'up' button, the faster the piston moves, and the faster the ascent rate?

Oh, and here is a link that discussed this same topic two years ago (give or take 10 days).

That’s the guy. Control circuits are easy, programmable descent rate, ascent rate, interface with a computer and control your deco, (or do your ratio-deco calcs and conrol you dive) keep it up and you can slap the whole thing an a scooter with a camera and not have to get out of bed … oh, that’s right … that’s an ROV!

I have been looking at using rigid ballast tanks to maintain perfect neutral buoyancy for a wile. With today’s integrated computers that read depth and tank pressure it is very technically feasible to have an automatic ballast system that would compensate for wetsuit compression and the tank weight change due to air consumption.

With such a device I would be able to dive like I did as a kid in the Caribbean. With minimal thermal protection, I was always basically neutral and I swam in a true three dimensional world (no BC ever needed).

Back in the late 70’s Dacor had the Nautilus CVS (Constant Volume System). I own one. I bought recently to experiment with it. It is a rigid ballast tank device that you adjusted the amount of water and air in it to be neutral and a regulator added air as you went down and vented as you went up. Interesting idea but it had no means of compensating for wetsuit compression or tank weight change.

The concept of an automatic compensator is very sound and I have been working on some of the details (I am mechanical and an electrical engineer), but the cost and complexity may keep it from ever been produced.

On of my concepts would pump water in and out of the rigid ballast tanks. The computer would be pre-programmed for the compression of different wet suit thickness and types. In addition it would have data for different tank sizes. Sounds complicated doesn’t it. It really isn’t.

Next summer I may test a very simple rigid ballast system using capped PVC pipes that I would manually flood when I am returning to shallow water and my tank is closer to empty. This will allow me to carry less compressible air in my bladder BC at the beginning of my dive. Therefore, less buoyancy fluctuation for our shallow dives here in Maine with a 7 mm wetsuit (14 mm around my torso).

The CVS was horrible, huge drag and the inertia when it had water in it was terrible. Way too much buoyancy as I recall.

 

[Luis H]

The CVS was horrible, huge drag and the inertia when it had water in it was terrible. Way too much buoyancy as I recall.

The CVS had many flaws, but at least someone was thinking out the bag…I mean box.


Rigid ballast tanks are very common and very successful in submarines and ROV (like you mentioned).


IMHO, there was a lot more different diving gear (like the Nautilus, etc.) that was tested back in the 70's. Now a days most gear seems kind of boring. Probably because of liability, very few dare to think out the box.

 

[Luis H]

A couple of years ago I had the opportunity to play around with one of these. Unfortunately it didn't meet our needs.

However, it uses a mechanism that I believe is similar to the ROV mechanism mentioned above. It's a simple electric ram working against a sealed air chamber. When the ram compresses the air in the chamber, it sinks. When the ram expands the air, it rises. No venting, no pumping.

This particular device just dives and surfaces, but precision depth control would be possible with precision ram control.

I don't think you would have to worry about electronic sensors and control. Just have 'up' and 'down' buttons. When the diver wants to rise, he holds the 'up' button 'til he reaches the desired depth. Opposite to sink.

However, you would probably need to make it so that the rise and dive rates are variable. Maybe pressure sensitive switches? So that the harder the diver pushes on the 'up' button, the faster the piston moves, and the faster the ascent rate?

Oh, and here is a link that discussed this same topic two years ago (give or take 10 days).

Since the surrounding water is basically incompressible, any buoyancy control device will only help you be neutral, positive or negative. It can also control the magnitude of how positive or negative you are.

IMO what it should not do, is trying to control you position as a function of depth. This is the equivalent to balancing on the ball of one foot. It can be done, but you are always making minor adjustments. Those minor adjustments are better done with your lungs. It becomes second nature once we are closer to being neutrally buoyant.


Added: Actually, if you are close to neutral all you need to do is swim in any of the three axis. It becomes a true three dimensional world. Were there is no difference were up-down or side to side is. Its is very cool when you actually have to look at your bubbles to know which way is up.