I just finished setting up my paintball CO2 system, so here is a brief guide for anyone else interested.
First, a list of parts:
-Cornelius primary regulator for CO2............................................... ...... $33.95 shipped
-20 oz. tank w/ SmartParts inline on/off valve (install separately)............. $25.00 shipped
-Needle valve (plus necessary adapters)......................................... ......$25.00 shipped
-Glass check valve and bubble counter........................................... .......$12.70 shipped
Regulator off eBay, tank off a paintball forum, needle valve and adapters from Rex Grigg and Ace Hardware, check valve and bubble counter from AquaticMagic for a total of $96.65.
Here we go!
Here's the top of the 20 oz. paintball tank. The brass part is the on/off valve. Don't buy a paintball tank that is manufactured with an on/off valve, which are notorious for leaking. Instead, buy the on/off valve separately and have it installed at a paintball shop, or buy a tank second-hand that already has the on/off valve installed for you. Note that if you buy the tank and valve separately and new, it will be close to 40 dollars, so check out a paintball forum's For Sale section. The black knob is what you turn to either open or close the valve.
Here's the same picture, except if you look closely, you'll notice a black rubber ring on top. That's an O-ring, and that's the only thing I've found that will prevent leaks once I've screwed the regulator on. The reason why conventional washers won't work is because of the threading on the on/off valve. Notice how the threading begins about 5 mm down from the top of the valve. Include a 1-2 mm thick washer, and the separation is too large and your regulator nut won't thread. The O-ring I used was a #60-RING, and I found it in my local Ace Hardware store.
Now, on to the regulator. Because the on/off valve has CGA 320 threading, you can use any primary regulator. This means if you decide to change from paintball to a larger conventional tank, you won't need to buy any new adapters. I was fortunate enough to buy a NIB Cornelius regulator for cheap on eBay. The left side of the regulator has a needle valve and an adapter for 3/16" tubing, both from Rex.
Below is a close-up of one of the regulator ports. My regulator came with a weird piece installed in the 1/4" port, so I had to remove it, which took a lot of elbow grease and some help at Ace Hardware. With the port empty, I screwed in a 1/4" to 1/8" adapter (the first piece of equipment with teflon tape on it), and screwed in my Clippard needle valve, which came adapted to 1/8" (the second piece of equipment with teflon tape). The needle valve is connected to regular airline tubing, and if you look at the previous picture, that piece of tubing is connected to another adapter that lets me use my 3/16" Tygon tubing.
With everything set up, my paintball tank registered just under 600 PSI, and there were no leaks that I was aware of. I'll post a complete picture once I get back to my dorm; I don't have my check valve/bubble counter at home
Please understand that if you're thinking about going the paintball route, it won't necessarily be significantly cheaper than a full rig. This is more an issue about portability and convenience (my paintball tank can be filled at a close-by sporting goods store for $2.50) than economical concerns.
That's it! I will update if any of my information is incorrect. Other than that, there's nothing to say but ENJOY!!