Drysuit Inflation Bottle: When to Use Argon and How to Mount It

Cold water. A long decompression. Back gas with helium in it.

Every time you add gas to your suit, you're adding something that pulls heat out of you. Helium carries heat away far faster than air. So the colder and longer the dive, the more every squirt of back gas into your suit costs you.

That's the problem a small bottle on your backplate solves.

What is a drysuit inflation bottle?

A small, separate cylinder that feeds your drysuit and nothing else. It has its own first stage and one short hose to your suit valve. Most divers fill it with argon. Some use air.

It doesn't replace your back gas. It replaces your back gas as the thing you put in your suit.

Do you need one?

Probably not yet.

For most recreational drysuit dives, your back gas inflates your suit just fine. On doubles, the drysuit hose comes off the left post. On a single tank, it takes a spare low-pressure port. See Doubles Hose Routing.

A separate bottle starts to make sense when:

• Your back gas contains helium. That's the big one. Cold water, long bottom times and helium mixes are exactly the reasons divers look for another way to inflate their suits (Halcyon).
• The dive is long and cold, with a lot of time spent still at your stops.
• You want suit gas separate from breathing gas, so a suit problem never touches the gas you breathe.

Does argon actually keep you warmer?

Let's be honest about this one.

The comfortable belief: argon is the secret to staying warm.

The truth: argon conducts heat a little less than air, so it insulates a little better. How much difference you'll actually feel is debated. Your undergarment, your hood, your gloves and how much you move matter far more.

The real win is what argon replaces. Helium in your suit is a heat thief. Keep it out.

Where should you mount it?

On the left side. Your suit inflator hose already lives on the left, under your left arm. Your left hand already does the suit work. Keep it all on one side.

GUE's configuration standards say the same thing in one line: small bottles go on the backplate, larger supplies on the diver's left back-gas cylinder (GUE equipment configuration).

Within reach. You need to reach the valve with your left hand, in your gloves, with your doubles on. Mounted valve down near your hip is a common way to get there. Try it on land. Then try it in the water.

Out of the way. Keep the bottle clear of your manifold, your left hip D-ring and the space your stage and deco bottles need. Your stage bottles hang on the left too.

Bolted, not hoping. Mounting kits strap a 6 cubic foot bottle directly to the backplate. Halcyon also offers a 14 cubic foot kit that mounts to the cylinders. A bottle that shifts during the dive isn't mounted.

What regulator does it need?

A first stage with an overpressure relief valve. The regulator feeds a single low-pressure hose, and if the first stage starts to creep, the relief valve vents the excess instead of letting pressure build in the hose.

Add a short hose, routed under your left arm to the suit valve. No loop.

What can go wrong?

• It runs out. A small bottle doesn't last forever. Know how full it is before you dive, and know what you'll do if it runs dry mid-dive.
• Somebody breathes it. Argon is not breathable. Mark the bottle clearly, so nobody grabs it as a pony bottle. Ever.
• The valve is closed. Like any valve, it has to be open to work. Check it before you get in.
• You can't reach it. If the valve is out of reach, you can't shut it down when the inflator sticks.

Is it time for one?

Ask yourself honestly. Are you breathing helium yet? Are your dives getting longer and colder? Is your suit the thing you're thinking about at the end of every dive?

If the answer is no, spend the money on a better undergarment and better drysuit buoyancy control. If it's yes, set up a bottle and practice with it before the dive that needs it.

Either way, it starts with real drysuit skills. That's the Drysuit Diver course.