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Choosing the correct cylinder for youUpdated 2 years ago

Getting the right tank for you can be a daunting choice when you look at the amount available on the market but it is actually quite simple! All you'll need to do is choose what material is best for you and then the size you require - Both of which we will break down for you here!


Cylinders are typically made from either Steel or Aluminium and we'll examine the difference here.


Steel is inherently a stronger, denser material than Aluminium which results in a few key differences;

  • Steel Cylinders are filled to 232Bar as standard and 300Bar versions are available
  • Steel Cylinders tend to be slightly smaller than an Aluminium cylinder of the same air capacity
  • Steel Cylinders are heavier both on the surface and underwater and as such exert more negative buoyancy
  • Steel Cylinders are more durable than Aluminium and more resistant to scratches and dents

Steel Cylinders are most commonly used by divers wearing thick exposure suits which make them more buoyant, so the fact that Steel is heavier in the water becomes an advantage as you can slightly reduce the amount of weight used.

The fact they can be manufactured up to 300Bar is also strongly desired by some more technical divers, it is worth noting that to make a 300Bar cylinder the walls of the cylinder become thicker which causes the cylinder to become a lot heavier than its 232Bar alternative!



Aluminium is lighter, more corrosion-resistant material than Steel which results in the following way;

  • Aluminium Cylinders are limited to 207 Bar with no higher pressure options available
  • Aluminium Cylinders will be slightly bigger than a Steel Cylinder of the same air capacity
  • Aluminium Cylinders are lighter than Steel on the surface and underwater, in fact, an almost empty Aluminium cylinder become positively buoyant!
  • Aluminium Cylinders are more prone to external damage which may cause reduced lifespan if they and handled roughly

Aluminium Cylinders are commonly used when travelling or diving abroad in warmer climates where you will be wearing a thinner exposure suit and will require less weight to become correctly weighted.
They are also used as Stage Cylinders or as a backup reserve carried by technical divers as they are lighter and easier to manage in the water.



The size of the cylinder is normally decided by the application you will be using it for.
Here is a breakdown for Steel;

  • 15 Ltr - The largest size available and also the heaviest! Typically recommended for people with high air consumption or for longer, deeper dives.
  • 12 Ltr - The most common size as it is a good balance between size and weight. For typical UK diving, we would recommend a 12Ltr 232Bar Cylinder.
  • 10Ltr - Slightly smaller than the usual 12Ltr, commonly used by people who may struggle to handle the weight of a 12Ltr or 15Ltr cylinder.
  • 7Ltr - These tend to be used as a backup or stage cylinder and are usually manufactured long and narrow to match these applications.
  • 3Ltr - The most common backup or Pony cylinder, it holds less air volume than a 7Ltr but is widely considered as more than enough for most emergency situations.

What about a Dumpy Cylinder? It is possible to get a "Dumpy Cylinder" which is a 12Ltr which is shorter than the usual 12Ltr cylinder, but also has a larger diameter! Its most common application is for shorter people who are worried about knocking their head against the tank valve when in use.

300Bar or 232Bar? You can get 12Ltr, 7Ltr and 3Ltr cylinders in 300Bar variants, as mentioned earlier they will be much heavier but allow for higher air capacity. This is mostly used in Technical Diving and is only available in DIN fittings - Not all regulators are made for use with 300Bar!

Aluminium Cylinders use a slightly different sizing system to Steel but it can be roughly translated;

  • 11Ltr - The most common Aluminium cylinder for usual diving purposes
  • 7Ltr - Usually used as a stage or back up cylinder, it also has application to technical diving.
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