All you need to know about purchasing a Cylinder

by Tracey Roberts
All you need to know about purchasing a Cylinder

 

Purchasing Scuba Cylinders – New or Secondhand

There is nothing wrong with purchasing secondhand equipment. In fact, it can be an excellent way for divers to build their own kit over time. However, when it comes to cylinders—whether for scuba diving or any compressed air application—there are several important considerations you must understand before buying.

In the UK, cylinders must comply with specific inspection and safety regulations before they can legally be filled with air.

Cylinder Markings

 

Is the cylinder in test?

To be filled, a cylinder must be “in test” (within its current inspection period).

It is important to note that even a brand-new cylinder can be out of test if it has been stored for some time before sale.

Cylinder manufacturing dates are stamped on the cylinder neck (e.g. 2012/02 = February 2012). From this date, inspection cycles apply:

  • With a gauge fitted to the pillar valve: typically a 5-year test cycle

  • Without a gauge: typically a 2.5-year test cycle

If the current date exceeds this cycle, the cylinder must have:

  • A valid inspection label from an approved test centre (e.g. IDEST), and/or

  • A physical test stamp on the cylinder neck showing the most recent test date

If neither is present and the cylinder is out of date, it cannot legally be filled.

The good news is that out-of-test cylinders can usually be retested—something we can arrange—but it is always best to buy a cylinder that is already in test.

Does the valve match the cylinder?

Cylinder working pressure and valve rating must match:

  • 232 bar cylinder → 232 bar valve

  • 300 bar cylinder → 300 bar valve

This marking is usually engraved on the valve itself.

If there is a mismatch, filling stations will refuse to fill the cylinder for safety reasons.

Is the cylinder made to UK standards?

Cylinders used in the UK must conform to recognised standards such as BS5045 or equivalent European approvals.

If a cylinder is marked DOT, it is typically manufactured for the US/Canadian market and may not be acceptable for filling in the UK.

If the correct certification is not present, the cylinder will not be filled.

Types of cylinders

Cylinders are generally made from:

  • Steel

  • Aluminium

  • Carbon fibre composite

Carbon fibre cylinders have additional considerations:

  • Certification details are embedded in the composite wrap

  • They typically have a maximum design life (often ~15 years)

  • Any damage or tampering with the outer wrap will render the cylinder unsafe and unserviceable

Secondhand cylinder condition

Physical condition matters. A cylinder that is heavily corroded, dented, or poorly maintained represents a potential safety risk.

That said, cosmetic issues such as paint damage or surface rust can sometimes be rectified during servicing, including blasting and repainting.

A bargain is possible—but only if the cylinder is structurally sound and serviceable.

What should you do when buying secondhand?

The safest approach is simple:

Buy a cylinder that is already in test and correctly marked.

You will typically pay slightly more, but you gain peace of mind and avoid unexpected servicing costs.

Can a filling station refuse to fill a cylinder?

Yes.

Even if a cylinder is technically in test, a filling station can refuse to fill it for safety reasons. Common causes include:

  • Rust or corrosion

  • Poor general condition

  • Missing or unclear markings

  • Valve or certification concerns

Safety always takes priority.

Can I fly with diving cylinders?

Technically, yes—but it is rarely practical.

If you do travel with cylinders:

  • They must be completely empty

  • The valve should be open for inspection

  • They must go in checked baggage only

  • They should be properly protected (padding/bubble wrap)

  • Airline policies must be checked in advance

However, in most cases:

Renting cylinders at your destination is significantly easier, cheaper, and more convenient.

Final advice

If you are unsure, consider investing in further training such as an Equipment Techniques specialty course, which will help you better understand:

  • Cylinder safety and inspection requirements

  • Basic equipment maintenance

  • How to identify issues before they become costly problems

A little knowledge goes a long way in preventing unnecessary expense and improving dive safety.

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