How To Build Your Own Diving Lung

[herman]

There you go.

Those bottles look like they have flat bottoms and if so it's unlikely they are steel. Most likely they are AL 50's. You can find out for sure if you can get the ICC number off of them if it's ICC 3 AA they are steel, otherwise they are aluminum. Sure wish they were local to me, you would not have to worry what they were.

Hot water bottle, you might have been thinking of this:

In case anyone thinks that is a joke, that really is a working rebreather, I have had that very one in my hands. Tom happens to be local to me and is a well known rebreather expert. You should see some of his vintage rebreathers.

 

[Thalassamania]

Just the picture is kinda weird ... I had no intent to denigrate either Tom or his device. Tom's work is brilliant, I'm planning on building two.

 

[herman]

Do you happen to know about when it was publlished? I couldn't find it on either the Popular Science or Mechanics archives. The hot water bottle sounds sorta familiar for some reason.

I'm currently trying to come up with something that I can use in my swimming pool, without spending any money (saving up for the recession that's coming). I considered using some sort of oilless compressor connected to a second stage with some sort of inline filter to catch any metallic particles coming from the piston/rings etc. I read some posts about hookahs and couldn't find any halfass devices that anyone thought was safe to use. Perhaps a bellows would work.... I figure I need AT LEAST 1 cfm @ 120 psi if I don't exert myself. 2 cfm would probably be a lot better.

OK, so I come from a long line of rednecks.

You don't need nearly that much flow. Remember, you need say 1 cfm at atmospheric pressure- you breath air at ambient, not at the IP of the reg. 1 cfm at 120psi works out the be about 8 cfm at ambient or 8 times what you need. Try to suck down 1cfm at 120psi and you will inflate like a balloon. What you do need to do is to reduce the spring pressure in the second stage which will allow you to get a reasonable cracking pressure at a much lower pressure in the system. Then you can run your system at a lower pressure which in turn will increase the flow from your compessor. Around 50 psi seems to be about right. A compressor capable of around .5 cfm at 50 psi should do nicely. You will also want some form of accumulator to hold any excess air. This way you can start the pump a little early and build up some reserve air for harder work periods, plus it removes the pulsating effects of the compressor. A high volume "truck" type tire pump ran at something over 12 volts.....18v (3x 6V batteries) may be the ticket...that will make the compressor run a little faster than normal but it should not be too hard on it. You will also need a pressure relief valve to prevent explosive overpressurizing your accumulator or better yet a control switch that will allow the compressor to cycle, reducing battery usage and allowing the compressor to cool.. Just ideas off the top of my head...it's not like I have a prototype on my work bench or any such foolishness.

 

[herman]

Just the picture is kinda weird ... I had no intent to denigrate either Tom or his device. Tom's work is brilliant, I'm planning on building two.

I didn't mean to imply you were, sorry if it came across that way. You appear to know...or at least know of Tom but you can see why some would think that was a joke. He is a brilliant man and a really nice guy to boot, I really enjoy every chance I get to sit and talk with him.

 

[JamesBon92007]

Those bottles look like they have flat bottoms and if so it's unlikely they are steel. Most likely they are AL 50's. You can find out for sure if you can get the ICC number off of them if it's ICC 3 AA they are steel, otherwise they are aluminum. Sure wish they were local to me, you would not have to worry what they were.
.

Gee whiz, I didn't even notice that the tanks were flat on the bottom! The guy selling them said they were steel and stamped 2250 so aluminum wasn't a possibility. I just didn't get a good feeling about the whole deal so I'm passing on it. He also seemed reluctant to disclose the original hydro date. Heck, I'm using a tank that was made in 1963 so I don't know why he wouldn't say.

I think I missed something on the rebreather story--was there some more information or a link somewhere? Naturally I want to know more

 

[JamesBon92007]

You don't need nearly that much flow. Remember, you need say 1 cfm at atmospheric pressure- you breath air at ambient, not at the IP of the reg. 1 cfm at 120psi works out the be about 8 cfm at ambient or 8 times what you need. Try to suck down 1cfm at 120psi and you will inflate like a balloon. What you do need to do is to reduce the spring pressure in the second stage which will allow you to get a reasonable cracking pressure at a much lower pressure in the system. Then you can run your system at a lower pressure which in turn will increase the flow from your compessor. Around 50 psi seems to be about right. A compressor capable of around .5 cfm at 50 psi should do nicely. You will also want some form of accumulator to hold any excess air. This way you can start the pump a little early and build up some reserve air for harder work periods, plus it removes the pulsating effects of the compressor. A high volume "truck" type tire pump ran at something over 12 volts.....18v (3x 6V batteries) may be the ticket...that will make the compressor run a little faster than normal but it should not be too hard on it. You will also need a pressure relief valve to prevent explosive overpressurizing your accumulator or better yet a control switch that will allow the compressor to cycle, reducing battery usage and allowing the compressor to cool.. Just ideas off the top of my head...it's not like I have a prototype on my work bench or any such foolishness.

.5 cfm @ 50 psi sounds a LOT easier to come by (cheaper) than what I suspected was needed. I actually thought of the pressure relief on my own :shocked2: As for the accumulator, where you thinking of a tank connected to the compressor and the air hose coming from there to the second stage? I sure didn't think about using a weaker spring in the second stage--I can see now what you mean. After I get it working then I'll see about a pressure switch--must be one in a box in the garage somewhere. I just happen to have a bunch of 6 volt deep cycle batteries but I would have thought 18 volts might be a bit much for a 12 volt motor, but yea, that should greatly increase the flow rate!

 

[herman]

.5 cfm @ 50 psi sounds a LOT easier to come by (cheaper) than what I suspected was needed. I actually thought of the pressure relief on my own :shocked2: As for the accumulator, where you thinking of a tank connected to the compressor and the air hose coming from there to the second stage? I sure didn't think about using a weaker spring in the second stage--I can see now what you mean. After I get it working then I'll see about a pressure switch--must be one in a box in the garage somewhere. I just happen to have a bunch of 6 volt deep cycle batteries but I would have thought 18 volts might be a bit much for a 12 volt motor, but yea, that should greatly increase the flow rate!

I am thinking of maybe 2 lengths of 6 inch PVC pipe, 2 to 3 ft long, connected together with T's and 2 to 3 inch cross members, the cross members would create a platform, provide a crossover path for air and add to the tank volume. 6 inch schedule 80 pipe is rated for 280 psi so using it at 50 to 75 psi should not be a problem. With a plywood base or some type of plastic tub attached to the cross members the pipe would serve as a floating platform for the compressor and batteries and as a reservor at the same time. 18V is a little high but the average auto system runs in the 14V range so it's not that much high. You could add some form of voltage reduction if you really wanted, a length of wire would add a couple of volts of reduction or a simple voltage regulator circuit could be built. Besides, this is really a toy, not serious diving gear so if you smoke a $10 compressor or 2 during a summer, so what........ohhhhh twin compressors with staged pressure switches.....or a low pressure override that kicks in the 3rd battery if pressure gets too low...I could get wild with this given a little spare time.

 

[JamesBon92007]

I have to stop myself sometimes on these kinds of projects and remember what my original intentions were. I looked into cheap oilless pancake compressors (Harbor Fright) and for about $40 you can get something that would probably work, according to what you told me. It would already have a reserve tank and pressure switch but would run from 120 VAC instead of 12 VDC, but for me that's not an issue. It could still be portable if it doesn't draw too much power for a small (800W or 1500W) inverter. I've looked at some of the "high flow" tire inflators but they rarely give the flow rate so it's kind-of a crap shoot.

 

[DaleC]

What about just buying a 25' hose and a tank on the surface? A HP130 would give you a lot of bottom time in the pool!

As for a small compressor with a reserve; my freind who fills my tanks got just such a unit given to him a little while ago. It was used on board a boat to clean the hull etc... with a long hose. We were discussing how much time the diver would have if the compressor crapped out (the reserve tank was fairly low pressure IIRC). Next time I go for air I will try to remember my camera and will post pics here for you.

 

[JamesBon92007]

Mainly I was trying to come up with something that wouldn't use up air from my scuba tanks so I wouldn't have to go get them topped-off before I could use them. Aside from that a tank and a long hose would certainly do the trick.

I hope the tank on your friend's compressor is bigger than what I was looking at--I doubt it would hold more than a couple of breaths. But I'm pretty good at making free ascents from five feet As Herman pointed out if you have, say, five cubic feet of air in a tank at 100 psi that will expand to a lot more at ambient pressures so I'd guess it would last long enough to realize the compressor quit and start making an ascent.