Important note: One should never ever attempt to blend diving gases without proper education, qualifications and safety protocols in place. One should also never ever dive any gas or gas mix without proper Scuba Diving education and training from a recognised agency.
Unfortunately due to illness I am stuck ‘onshore’ today while my club buddies head for what is likely to be a great dive at Hook Head, blast my sick stomach!
I thought I would take this opportunity to write up a brief report on a recent conversion of a common garden shed into a gas blending station. I had recently purchased a second hand Maximator Gas Booster pump and decided to install it along with my compressor and blending gases in the humble shed rather than in the house… for obvious safety reasons.
The shed began life just like any other common garden shed – it had become an oubliette for items that only saw use once in a blue moon... my gardening skills are at the same level as my ballet… non existent.
I proceeded to empty the shed and clean it out of all the “stuff” stuffed into it. Thankfully this went without too much difficulty and we found a suitable storage space for a few critical items at the back of the sovereign territory of the ‘Scuba Diving room’. This is a room in the house where I had previously stored the compressor along with all my other gear and got more than a little fed up having to go up three flights of stairs with my cylinders to get topped off… really what was I thinking!?!
With a nice clean empty shed its time to install electrics and lights – big thanks go out to Davey for doing the electrical work for me… great installation :)
Then its over to my good self to begin the conversion in earnest… my top priority was obviously to install a laptop with iTunes, so I could whistle while I worked. The other obvious reason to put in the laptop was to load my gas management software to instantly run my gas blending instructions when needed. Fire extinguisher and fire blanket also go in.
Next I installed the Gas Booster (centre left of picture below). This was tricky as the charge and fill whips had fixed orientations coming from the booster head. I decided to orientate it by fixing it to the side of the shed rather than resting on the floor… as this allows the whips run in fairly clean straight lines to the Gas storage cylinder, the drive gas and the receiving scuba cylinder without creating any major clutter in the shed while operating.
Then its time to run a test fill of a single tank… just to see if I am happy with the basic layout I had been planning.
After the test run I moved a few things around a little. The O2 and He are stored outside but within easy reach of the Gas Booster whip :)
So the system is up and running… at the moment I am not ‘banking’ any gas as I am only blending for myself. The method I am using is partial pressure blending with a Gas Booster to ensure maximum efficiency with gas usage. The Booster is rated for up to 300 bar and is 100% O2 compatible. I normally fill my steel twinset 12L cylinders to 240 bar and my Aluminium stage bottles to 200 bar.
To reach a desired mix I simply analyse the content of the cylinder I wish to fill (Analox Trimix analyser)… input the mix and it’s pressure (bar) into my gas blending software while also inputting my desired mix and intended pressure (bar). For Helium I usually use a 10% fudge factor to allow for the density offset. Then its simply a matter of following the instructions from the software. I also ensure to always use tape on the cylinder I am blending in and note the addition of any gas into the cylinder by hand. I also make sure the cardinal rules are always followed “Never dive a gas mix that you have not analysed yourself – and always mark your cylinder with the appropriate MOD”.
I think it was George Irvine from WKPP who said “the only way you are going to kill a smart person is by breathing the wrong gas”… so it is vital that at all stages you make a record on the tape placed on the cylinder during the blending process… logging the gas you have put into the cylinder at each stage. Never allow yourself to get distracted from this basic safety protocol. Despite using a computer to blend, you must log it on the cylinder itself and the cylinder must also always be analysed before diving it. Never guess what's in a cylinder… always analyse and label it.
I usually use the gas booster to facilitate the blending process by boosting of a specific level of He and O2 in pressure (bar) into the cylinder and then top the mix off with air from my compressor. This means I never have to “dump” gas out of my cylinders before blending and so I am saving all my gas… always important when dealing with expensive Helium. The booster also means that I can drain down the storage tanks to 5 bar… rather than handing back He cylinders with 60 to 80 bar back to BOC… that was heartbreakingly expensive.
The Gas Booster is run utilising compressed air… I use my old Fabre 15L single cylinders with an Aqualung Legend first stage to supply the drive gas to the booster.
I use a two stage filtration process on my compressor (Bauer Junior II) with a personal filter installed on the fill whip (supplied from Undersea UK). As I am partial pressure blending I do everything possible to ensure to avoid Hydrocarbon build-up inside my cylinders and I annually have all my cylinders tested and O2 cleaned. I also use a water bin when filling any cylinder to facilitate efficient cooling while blending… this helps the efficiency of the fill.
Finally the shed is suitable for this task as it has two doors… it therefore always allows a ‘safe’ exit route in case of emergency. Ideally I would have liked this to be a “concrete” structure… but we can’t always get what we want :) For the moment this system is running very successfully. I also installed a motion sensor alarm and have it linked to the house alarm system – call me paranoid :)
See an earlier related post on this blog regarding “a brief overview of Partial Pressure blending”
Important note: One should never ever attempt to blend diving gases without proper education, qualifications and safety protocols in place. One should also never ever dive any gas or gas mix without proper Scuba Diving education and training from a recognised agency.
