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With the two questions on the list I thought I'd pass on what is practiced in the real world. I know about 6 or 7 people/shops though out the US that mix gas. No matter what you read as the best method mixing gas all the people I know are using partial pressure mixing. All basically use the same stuff. The equipment is expansive so I imagine the number of private individuals doing this is low. The first thing you need is a compressor with standard air filters. On top on of the standard filter you need a special filter to further remove more hydrocarbons and moisture down to the IANTD/ANDI standard. Now you have what the industry refers to as "Hydrocarbon Free Air". These filter are typically made by Lawrence Factor. The next thing your going to need is some O2 from either your local welding supple house or Medical supple house. Which one you used is up to you. They are both fill from the same manifold it's the handing of the bottles that is different. You will need Helium and Argon for trimix. Now if your just going to do nitrox filling with empty tanks with a low PP of O2 you might not need a Haskel booster pump. But if your going to do trimix, topping off nitrox bottle and argon fills you will need this piece of equipment. It is an air driven booster pump. It has an input, an output and a (low pressure 160 psi) drive gas input. This pump's input can be hooked up to any gas supply Hydrocarbons free air, Nitrox, Helium or Argon. and then be transferred into another cylinder. The pump can crank the output pressure well over what your tank is rated for. One thing to take into consideration is the volume of drive gas needed to operate this pump 20-30 cfm. If you use a scuba tank and welding reg. for drive the tank it might last 5 min. How do you measure the exact pressure of the gases? On the fill side you need a high accuracy gauge. The people I know are using a 6 inch Permical 1% test gauge. It has divisions down to 20 psi but with a good eye you read it down to ~5 PSI. The last thing you need to do after filling a tank is analyze the gas with an O2 analyzer. Most places have three analyzes setup. This is incase one the analyzers is not functioning. The three that are common to scuba are the Mini OX, Teledyne and INATD sells Aquatronics analyzer. As for the numbers most people use a spreadsheet or computer program. These are very simple programs. They are very helpful if some some has residual gas in there tank and does not want to start from scratch. Programs also keep the error rate down Ie. simple math errors. The two that I've seen differ only by a few psi. Now that you have all the tool all you have to do is fill your tank. If you are using PP filling and starting with O2 the tank must be O2 cleaned and have O2 compatible O ring. Tanks must be allowed time to cool back down to ambient temp. after each step. If its fill out of a storage cylinder your tank doesn't need this. IANTD recommends if the PO2 is less than 40% cleaning is not needed. Directly from Johns Msg. I agree 100% WARNING - if you are new at this you should at very least become familiar with oxygen cleaning and safety rules before you even mix nitrox. Better yet, take a nitrox course; these are now widely available. You will avoid learning from the costly and sometimes fatal mistakes of others. Homebrew nitrox and trimix can be done safely, but you should be aware of the physiological concerns, which include DCS and drowning from CNS tox-induced seizures, and physical concerns, which include fire or explosion from exposing O2-incompatible diving gear to high pressures of O2. Now I know I've left out a few bit. This is general information only not a set of instructions. So no flames please, constructive comments are welcome.
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