[gwilson]

Originally Posted by Dave Abraham

You need to find a new LDS, if the cylinder is in test with a valid O2 sticker they should fill it no questions asked. As for "only if we've cleaned it ourselves" I've never heard so much crap in my life. I could get them to clean it, go away on a trip and get a fill from a compressor that is not double filtered and then take it back to them for a nitrox fill. They would be none the wiser.

There is however a common application for what you are trying to do. If you do a shallow dive on a rich mix eg nitrox 40 then get an air top up for a deeper dive the following morning. This is a common pattern on Red Sea liveaboards and at Scapa. It's useful to be able to calculate what pressure to leave in your cylinder so that you get the right mix for the deeper dive the following morning.

It's ok to come back from the shallow dive with too much gas as you can drain it down, but most places fill from a J cylinder so may not be able to add O2 if you need to come back with 120 bar and the J cylinder is already down to 80 bar. Pushing gas uphill is tricky unless you have a membrane system.

This particular one will not even fill brand new cylinders that are o2 cleaned unless they "perform" a clean themselves, including fully assembled brand new twinsets. Just a way of making extra cash, the other one up here will fill any cylinders he is happy with BUT does have a sign up saying any completely empty cylinder will not be filled unless you pay £11 for a visual inspection, this is a safety thing as who's to say you have not swapped valves due to damaging one and maybe put a metric thread valve in a imperial cylinder or vis versa, I know this as it was explained to me this morning by LDS owner.