Stages & Decompression Cylinders
Stage regulator choice
For a number of good solid reasons, have them the same as your back gas regulators
The best performing regs you have need to go on deco as this is when you are tired (and probably fed up of breathing from a reg). Also you are loaded with O2 and are now on a high O2 mix which is loading you even more. As such you don't want any breathing resistance which may build up CO2 and possibly trigger O2 toxicity. Remember with a good helium mix it will pretty much breath through any regulator so a bottom mix regulator could be of lesser performance than a deco mix - not that you'd do that anyway coz they are all the same - see above.
Feel and Colour coding
Some people say that a decompression regulator (for this read all the intermediate trimixs and nitrox and O2 regs that are on the various stages the dive calls for) should be a different feel and colour marked so that you can tell which regulator you are about to breath from. This is Iin my opinion one of these silly things - the discipline of turning on the stage cylinder that you need and knowing what you are about to breath is all that is required. When we dive all of our deco regs are rigged the same. And as such they can be put on travel mix or deco cylinders. This makes it easier to get the dive ready. We are not dependent upon getting this the right regulator on the right cylinder or something silly like that (this is what killed Bobby McGuire). When ascending look down at the cylinder necks to see which one you want as the MOD and mix is marked on the cylinder neck (isn't it??). Turn on the one you want, pull out the regulator attached to that cylinder (following the knob to first stage to hose) and wrap the hose around the back of your head so all regs feed from the right hand side (remember they are all the same), take out the regulator on your long hose from the mouth and breath the stage. If you have got the wrong one and it does not breathe more than one breath (so we don't have a toxicity issue) you put the long hose reg back in your mouth and sort it out. If the stage breathes its the right one, so clip off the long hose to the right shoulder D ring and continue the deco. We now have one reg in our mouth , one backup reg hanging below the chin where it always is and the long hose on the right shoulder D ring. You should then check your buddy(s) to ensure they have deployed the correct reg. As they have the cylinder markinged with MAX DEPTH on the side in 2 or 3 inch writing (don't they ??), you will be able to see which stage regulator has been deployed by checking the writing. If they have screwed it up you can assist them to get the correct reg and then later by giving them the name of the nearest golf club. If your scehedule calls for another mix or O2, you turn on the relevant stage, free up the regulator, swap to it as before then stow the now unused nitrox/travel regulator away down the side of its cylinder and then turn off that stage as it is not now needed.
First Stages & SPG's
The uses of a turret style first stage is a good idea as it allows the hoses to point down the cylinder whilst it is stowed and to be swivelled around to point upwards (toward the divers head) whilst in use. This allows a hose 4 to 5 inches shorter than a hose on a non swivelled first stage to be used. For this reason the Apex TX50 or the G250/Mk20 make good stage regulators. Always use a SPG, for decompression regulators. Many people consider that the regulator does not need a SPG as they gauge the cylinder on the surface and then plan to have enough decompression gas. They belive after all what can you do if you run out and seeing that you are about to run out is irrelevant ....
However as the decompression regulators and stage bottle regulators are set-up in exactly the same way, they are interchangeable until mounted to a cylinder, they will need a SPG as a stage is breathed during a dive to a fixed point. The best way to mount a SPG is via a short 6 inch hose as shown in the picture to the right. The gauge is bent back and permanently held in place with a piece of line - this does not damage the hose as it sets in the position. What does damage a HP hose is the constant moving and bending that a free hose will go through during its life.
Stage Cylinder mounting
stages mount on the diver's left hand side (unless carrying three, in
Why you don't back mount a stage / decompression cylinder
Consider two possibilities - the stage is carrying redundant back gas (in the case of many UK air divers this is often their ONLY redundant air source i.e. the 3l pony cylinder) or is carrying decompression gas (i.e. High % O2 or if done properly 100%)
In both scenarios above if the first stage fails a diver can still use the stage gas if, and only if, he has access to the valve (i.e. to turn it on to breath and off when breathing out) - this cannot be done if back mounted.
If its backmounted MOST systems used do not allow you, the diver, to remove and replace the stage by yourself if you need to get out a small hole in the wreck or a cave. Also consider becoming a key - the stage is on one side so you might fit in a hole going in, but you are the other way round when you come out - so the stage may catch/foul. A side slung stage can always be removed to get you out a hole.
When it is back mounted the stage cylinder creates additional profile in that it is along side your cylinder thus increasing your drag. When side mounted its in the lee of your shoulder and thus does not create additional drag
Finally hose routing. If back mounted where does the reg go - where does the SPG go ?? How do you distinguish between these and your back gas regs/spgs. When mounted as a side stage the SPG is visually seen as being attached to the stages first stage by a short HP hose, the regulator is held to the tank with bungees/car inner tube - so you know that this regulator and this SPG belong to this stage. If we did have to remove a side slung it comes away, all as one unit (i.e. no hoses attached to the diver). If you had to take off a back mount pony - what do you do with the hoses, regulator and SPG ??
If we ignore all the above - a small 3l pony may be a consideration for back mounting. However as bigger cylinders are used due to dive requirements e.g. 10l, it can no longer go on the back so has to be side slung. Thus why change a configuration and cause confusion ?
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