Scuba Cylinder Rundown

GRANT DONG

The 12-litre aluminium cylinder is by far the most popular, but this does not necessarily mean it is the right one for you.

Cylinders come in various sizes and materials, and you can set them up in multiple configurations Choosing the right cylinder for your dive is vital for your enjoyment and safety.

Sizes

The standard aluminium 12 L is an economical cylinder that offers an appropriate amount of breathing gas for most divers Younger or smaller divers, however, may struggle with the size and weight of an aluminium 12 L and instead be more comfortable with a shorter cylinder, such as an aluminium 10 L Divers who quickly consume gas may benefit from a larger-capacity cylinder, such as an aluminium 15 L, to extend their bottom time.

When choosing an appropriate cylinder size, consider factors such as the cylinder’s weight, gas consumption rate, anticipated dive profile, personal comfort, and how much gas your buddy may need if you need to share air in an emergency If the largest aluminium cylinders don’t provide adequate gas, consider switching to steel cylinders or a setup that allows you to carry multiple cylinders.

Materials

Understanding the differences between steel and aluminium cylinders is essential for choosing the right material for your needs Steel cylinders come in various capacities matching those of aluminium cylinders.

Whether full or empty, steel cylinders tend to be negatively buoyant underwater Aluminium cylinders often start negatively buoyant but eventually become positively buoyant as a diver consumes the breathing gas Although steel cylinders are more negatively buoyant underwater, they have thinner walls than aluminium ones and often weigh about the same, if not less, on land than comparable aluminium cylinders This buoyancy difference means divers using steel cylinders do not need as much lead to achieve proper weighting.

The final and perhaps most important consideration is that steel is much more vulnerable to rusting than aluminium Even small amounts of water in a steel cylinder can cause significant rusting and pitting, which can permanently damage the cylinder Minor oxidation may occur if moisture gets into an aluminium cylinder, but it is unlikely to cause significant damage Annual visual inspections are crucial for detecting corrosion before it becomes significant and leads to irreversible damage.

Configurations

The single-cylinder configuration we learned to dive with is sufficient for most dive conditions You can add another cylinder to your setup if you wish to have redundancy or extra breathing gas You can consider a mini bailout bottle with an integrated regulator Still, their limited gas volume and the possible lack of an appropriate submersible pressure gauge (SPG) restrict their usefulness. A 12-litre pony bottle is another option. You can strap it to the cylinder on your back or clip it to your buoyancy compensator’s D-rings. With their own first stage, second stage, and SPG, these pony bottles provide a completely redundant system with more breathing gas should the diver encounter an issue.

For more information on small bailout cylinders, see Jill Heinerth’s article “Air and a Spare”

(https://wwwdansaorg/blog/2022/03/26/airand-a-spare)

Back-mounted doubles may be a good alternative if you want a setup where the cylinders are more secure and provide more gas than a single-tank-and-pony configuration.

This back-mounted configuration consists of two cylinders with left- and right-handed valves interconnected by a manifold Each cylinder will have its own first and second stage, a BCD or drysuit inflator hose, and an SPG as necessary The benefit of this setup is that you have a completely redundant system that rests on your back, similar to carrying a single cylinder Suppose a regulator or cylinder has a catastrophic failure In that case, the diver can isolate the issue by closing the appropriate valve while still having access to the other cylinder as a gas reserve.

A sidemount configuration may be appropriate if you struggle to carry a heavy set of doubles or find it difficult to squeeze through narrow restrictions in caves or wrecks With sidemount, you fasten cylinders along your flanks through bungees and bolt snaps.

This flexible configuration allows you to quickly identify and resolve any issues because the regulators and valves are easily visible and accessible, unlike with doubles, where valves are located behind the head. Because each cylinder is separate, you need to occasionally swap regulators to maintain a similar pressure in each cylinder. The cylinder positions and flexible attachments can make it challenging to perform a giant stride entry or handle cylinders on a boat, especially in rough conditions.

As with all your dive gear, choosing the cylinder material, size, and configuration best suited for the diving you plan to do is essential to your dive safety and enjoyment. If you have any questions, do not hesitate to contact the experts at your local dive shop, who can work with you to customise a setup that works for you.