I've been following this thread for a while and haven't had such a good laugh for some time. You guys just crack me up! What are you trying to do - force us to all live in a nanny/police state? Relax and get a life for goodness sake!!! Firstly - I change the brakes on my own car without being a trained mechanic, so with that in-mind, I firmly believe that I can fully service my own washing machine and scuba kit without going on a course. And I do. My dive equipment manufacturer will sell me the bits if I ask them to. A full service kit for my Oxygen clean first stage cost me 17 quid (ish) Also, This is UK.rec.scuba, and the original question was asked by someone who lives in the UK, so lets concentrate on UK cylinders, regs. etc. Next, I do blend my own Nitrox at home. Mostly, I just use my cylinders of O2 for topping up my Inspiration Oxygen bottle, but I have in the past done a Nitrox fill for a friend. So, to do a Nitrox fill, you need a few simple things: Firstly some O2. We'll come to that in a minute. Next, a decant hose - Get one from AP Valves with a button gauge on it for about 80 quid, or one from Sub Aqua Products with a nice needle valve and 4 inch gauge for about 250. I have the former because (a) I'm a tight fisted Scot, and (b) I've successfully mixed Nitrox with the button gauge and an ordinary scuba regulator gauge. You'll need a friendly dive shop or your own compressor, and for good measure a handfull of common sense. On to the gas. For the most part, Oxygen comes in 4 flavours. Theres industrial (aka welding) O2, Diving O2, Medical O2 and Aviators O2. If you're willing to pay for Aviators O2, then fine, feel free. It's generally purer that the other 3 and has a much lower moisture content. Me? I use welding gas and have been using it for over a year now without a problem. A welding regulator has a one-way valve on it, so the chances if getting acetylene into an O2 bottle are like zero. Anyway, Acetelyne is dispensed at such a low pressure it's not a problem. If you did get acetylene into the O2 bottle, you'd soon know about it anyway. Well, for a few nano seconds at least. So whats the difference between the other 3? After a lot of calls and speaking to people and reading up on it, I am fairly cofident that the answer is: Nothing. All 3 types of bottle are emptied and a vacum is pulled on them. The are all filled from the same source which is gaseous O2 - Liquid O2 boils off and only produces something like 7 bar of usefull pressure - enough to run a deco chamber, but not enough to fill a J cylinder without a pump. So, they are emptied, vacumed and filled. Medical bottles are analysed and send out with individual tracking information. Diving O2 is batch analysed and sent out, welding gas is sent out... Thats why I chose welding gas. Sure the cylinders are really grotty, covered in grease and rust, but so what. It's whats inside thats what I'm interested in. So there you go, as long as you have the bits, the hose, the frindly dive shop who'll let you top them up, I'd say go for it. Don't forget the analyser, of-course and the math or table to work out how much O2 you need to put in, and as usual, do it slowly and don't rush it. I'd also say get your cylinder O2 cleaned every now & then. I know my welding tanks aren't O2 cleaned every year... And all this nonsense about Viton O rings is just that - Nonsense. Read all the Scuba-UK archives where that was thrashed out years ago and just use the ordinary O rings, and if you use fairy-up liquid to clean things, remember that it's hydrocarbon based and needs to be thoroughly washed off afterwards. (it also tastes foul!) If you can't hack the math, or get a table from somewhere, DDPLAN (http://www.drogon.net/ddplan/) has some mixing calcs in it. And where to get O2? Air Products is probably your best bet, maybe Linde next. Look them up in Yellow Pages. I pay 12 quid for a 50 litre cylinder to 200 bar and a fiver a month rental for it and 18 quid delivery regardless of how many bottles I exchange at a time. You can get better deals if you have more bottles. (Diving grade is 18 quid a fill) Have fun! Gordon -- Gordon -- This Gordon Henderson \ MIME mail? No thanks. is gordon@drogon.net \ "Learn the words!" and yes, Drogon *is* an anagram of Gordon! \ The Patrician; Ankh-Morpork. .