on board air w/ scuba for storage?

Ok here we go, i just got my ac pump adapted oer to onboard air with a 120psi pressure switch. I hae a in good condition yellow scuba tank. I know they need to be certified to be used and filled properly. but that is for like 3000lbs. Im talking 120psi and plan to mount in securely inside my top rack. what do you guys think? i know there are better bottles but i already hae this one. any one else doing something like this, filling a tank with a conerted ac? i would like to get some ideas. thanks oh and will this thing shoot like a missle with only a hundred pounds in it if it where to get knocked. although it would be hard to do inside my rack

With the right fittings you could certainly fill a SCUBA tank with 120 psi. It will just wont be near its (air) volumetric capacity. If you knock the top off it will probably move around (spin?) but the reason big tanks become projectiles is because they are highly pressurized; so no. You won't get a missile.

I run a Scott SCBA tank charged to 4500psi. I used a oxygen tank regulator to regulate it down to 0-200psi and hooked a hose to it. With that I can fill my 35" tires from completely empty to 37#s about 10 times. I use it all the time! Love it.

Since that's not what you're wanting to do I'll stop babbling about that.

Answer your questions...

No, the tank won't shoot like a missile with 120psi. Just strap it down either way. Yes, it will work but I think you'll be happier with a set-up like mine.

If you plan to use the first stage regualtor that's on it and you can find a fitting to adapt down to 1/4"npt then you can run the same regulator that I have. Then you can charge it to 3000psi.

Btw, the regulator came from Harbor Freight.