compressed air container - good or bad?

[wadester13]

My sub is being made from scratch. I have a small fire extinguisher that has been hydro-tested to 300 psi. I have cleaned it out and tapped it and have pressurized it to about 150 psi with no leaks. Is there any law against using this as a compressed air container in my sub? This sub is not for combat or compitetion only for my own interest and what I can make it do.
I have ordered a wireless cam for the sub which I plan on installing after my first few sea trials.
If this is a problem I can eaisly convert to another container.
Thanks for your comments (bad or good).

[feet wet]

A couple of questions come

A couple of questions come to mind relating to your post. How large is your boat, and perhaps more importantly ,how large is your ballast tank. Also how large is the extinquisher?
The amount of air contained in the presure tank @ 150psi may not give you very many "blows" of your ballast tank.
I am using a small scuba tank,I am a certified diver,that holds 11 cu/ft @2000 psi. Dropping the pressure down to 75 psi gives me an almost unlimited supply of air. Not so @ 150psi.

Jonathan Eno

[wadester13]

I am attempting to build

I am attempting to build a 1/32 L.A. class. It will be 11'-4" long and 11" in dia. the main ballast tanks are about 1.3 cu/ft. My air tank is 11" by 3". At 120 psi or so I filled 3 balloons (third one popped) and some left to spare but I dont know the equations for pressure drop in the tank to the pressure in the ballast tanks at a depth and the pipe size to use for how many seconds to blow without loosing air from the free flood vents. One or two blows would be good I think. The only reason I picked 150 psi was because I am using the guts from a 12V tire pump for an air compressor in my sub, it charges from 0 to 120 or so in about 2.5 minutes (not too impressive). I guess it will have to be trial and error.

[safrole]

I am confused. Will the

I am confused. Will the 12V pump be filling the ballast tanks, similar to the RCABS setup, or will the tanks be cleared with the compressed air of the extinguisher tank? Or do you have another, possible hybrid setup in mind?

I have not heard of any specific laws (in the US) about those small tanks. Usually federal regulatory warnings are posted on the outside of the containers. I saw none on my extinguisher, but I did see that it is rated to 585 lbs. Of course tapping a hole in it yourself scares me, unless you mean that you are using the stock hole and just tapped it for your fitting.

[feet wet]

If I understand your idea

If I understand your idea correctly, you plan on filling your pressure tank using the 12v compressor, blowing your ballast tank with the "high Pressure" air stored in the tank, right?
First off, you filled your balloons in ambient air, or underwater,if the latter at what depth? The deeper the sub when you attempt to "blow " the more air volume you will need, and you don't seem to be leaving yourself much leeway.
I think you need to sit with someone to figure the volume/pressure needed to satisfy that little ballast tank of yours while bearing in mind the depth at which you are likely to blow.
Just an aside, but on advantage to extra air is the ability to use it for other purposes. Mine also powers my snorkel and my 'scpoe independently. I've yet to run out, it is easy to refill, its cheap, and with a boat the size of what you are building you could use the battery for running around as opposed to running a compressor.
sorry to be long winded.
Cheers,
Jonathan Eno

[wadester13]

I am still looking to

I am still looking to see if there are any regs. The container was tested to 300psi and yes I modified the original fitting to accept a tire valve. The bottle itself has only been painted. If I drill any holes the hydro test might as well be down the drain and not trusted. Here is a pic.

[wadester13]

Any comments are welcome good

Any comments are welcome good or bad and all helps. My air tank is originaly for the blow. My masts (right now) will be powered by motors, just thought the movement would be more smooth. I will need a couple hundred pounds to achieve neutral bouancy. Weight is not a problem right now. I am looking at batteries rated for 12AH and above. This whole thing is going to be experimenting to find what is best. Like I said comments are welcome so (lol) please beat me down.

[feet wet]

Please don't take my comments

Please don't take my comments as beating you down,just some insight. My masts are powered by compressed air, but the speed was easy to regulate by controlling the volume to the ram cylinder as opposed to the pressure.
My 688 is 1/48th and did not need anywhere near what you suggested for ballast weight. Is your boat all dry hull or are you allowing for free flooding area. The latter will greatly reduce your ballasting needs.

Jonathan Eno

[wadester13]

I don't get hurt that

I don't get hurt that easy. It will be a dry hull. The reason is for equipment. I want to put torpedoes and possibly a motherboard. It will be kinda like a robot while deep. Do you have pics of your boat?