I use a Fixed Pressure Regulator made by Balloon Barron (120 lbs) with no gauges that I got from the local Welding Supply House (WSE in San Diego) for just under $30. You can also buy/rent your bottle there and get it refilled. They will have CO2, Nitrogen, Argon, Oxygen and just about any other gas you could want. Each gas requires a different valve for safety reasons, although there is some crossover. For example CO2 and Nitrogen have different valves. The difference is in the output coupling, threads and style. You can get adapters to convert one output to another for some applications. I have three CO2 bottles and one Nitrogen. I use the CO2 for just about everything in the field you can think of, Air Tools, Airing up tires and MIG Welding (the Miller 200 has its own adjustable regulator and gauges in the shop). The Nitrogen is used only for charging Shock Absorbers after rebuilds. The reason that you want to use CO2 over Nitrogen are several. CO2 is cheaper, safer and lasts longer. Nitrogen is stored in compressed form as a gas at up to 2000 PSI so breaking a valve off could be catastrophic. CO2 is stored in compressed form as a liquid at around 800 PSI. Because it is stored as a liquid the same size tank can hold more cubic feet of gas. The gas that is released from the tank is evaporated off the top of the liquid CO2 at an almost constant pressure of I think 600 PSI at a given temperature until all the liquid is gone. The Nitrogen bottle will have half the original pressure when half the original volume is used. The only way you can tell how much Nitrogen is left in the tank is by the tank pressure, so a gauge is necessary. With CO2 you can only tell how much is left in the tank by weighing it.
