Cylinders

The shoulder markings are a cylinder’s identity document. Read them to verify any tank is rated, legal and safe to fill — essential before buying used.

Steel stays negative all dive; aluminium swings positive as it empties. Why that one fact decides your lead and the cylinder’s role.

Working pressure decides how much gas fits in a cylinder. What the three ratings mean, when 300 bar is worth it, and the safety rule you can’t break.

The 12 L 232 bar cylinder is the default for most divers — here’s the simple maths behind tank size, and how to know when to size up.