SpudFiles

I could just use the boat's anchor and rope for the lowering system.

I don't really want to deal with pressurised tanks, but if I had to, how long do you think a 3" X 12" PVC tank at 100PSI regulated down to 1ATM would last me?

So if I added 2 check valves (C) to BLB's idea, air would come through the top check valve, down the pipe, through the other, into my lungs and exhaust through the bottom. Thanks for the help on that part.

C
I I
I I~~~~~~~
I I
I I
I I
C
I = Mouth
I I
Open Water

If you just want to mess around i have an idea for you. Once i was in the beach with one of my fire extinguisher guns, well i had the bright idea to return it to a regular fire extinguisher for a day, i felled it up to 150 or so and but some weighs on, the thing is that you have to push the lever ever so slightly because if not YOU DIE. It was fun for the 4 minutes it lasted.

M3NT4L wrote:If you just want to mess around i have an idea for you. Once i was in the beach with one of my fire extinguisher guns, well i had the bright idea to return it to a regular fire extinguisher for a day, i felled it up to 150 or so and but some weighs on, the thing is that you have to push the lever ever so slightly because if not YOU DIE. It was fun for the 4 minutes it lasted.

I like this idea the best.
I would modify the lever to open only so much.

A full 4 minutes on a relatively small tank, cool, I'd put a regulator on it though, maybe a tank with a ball valve barely opened might do it. I could refill it with a bike pump on the boat. Would it be possible to just use a really small hose, with like a 1mm hole at the beginning?

So basically, home made SCUBA. Maybe I'll put a tank in an old backpack to wear it, just something to screw around with.

Checkvalves take significant pressure to open, typicaly on the order of 3 PSI.
3 PSI is A LOT of pressure. (although you may be able to find more sensitive ones)

3 PSI is'nt really a lot of pressure, air at sea level is 14.7 PSI, so the extra 3 should'nt make too much of a difference. Maybe the ones that use flaps might be easier to open.

P.S. 777th post!

I wouldent use a bike pump if you want to go over 100 psi, unless you have a really good one. Today after reading this topic i modified it and put a locking system so that letting too much pressure get through wasent a problem. I attached a snorkel mouthpeice to it and put a longer hose. I straped it to my back and if you get the right ammount of air go then you can basicaly breathe as if you were outside the water.

That's awesome! A PVC tank with a ball valve should do the same thing right? I'm going to try and get a fire extinguisher though.

Can you show a pic of your system?

I dont have my cam till i go to my dad's but on saturday i will. I think the pvc thing will do the same thing but i think that it will be lighter and buoyancy will be a problem. And if you accidentaly smack the plastic tank against something you are risking it but with the steel extingushers you know it can hold 500+ easy.

I always wanted one of those little SpareAir emergency tanks.

What's wrong with holding your breath underwater?

Can you hold your breath underwater 4 minutes. my best was 1 minute 40 seconds and i couldent take it.

I could wrap the PVC in a towel or something to protect it. How much pressure does Copper hold?

For bouyancy, I could fill another PVC tank with something really heavy, what else is heavy besides lead, that's readily available? Maybe rocks.

sand is heavy. dirt is heavy.

I could use sand, not dirt though, if the weight chamber fills with water dirt kinda floats when you stir it at all.

P.S. Use grammar please, and don't change the topic about this.

Oh... I see my understanding.
I thought one checkvalve was upflow of the mouth, and the other was downflow.

Looks like both are upflow of the mouth... so WHY are they there at all? They arn't accomplishing anything...

Anyway, why shouldn't you hold your breath while using a [sc]uba?
If you take a breath at depth, and then acend, the increased air volume in your lungs could cause a condition known as "collapsed lung".

Not good for you.

(note that normal surface diving doesn't carry this threat, because you are limmited to the amount of air you inhaled on the surface)