What to look for when buying a used cylinder

Buying a used diving cylinder is a bit like buying a used car, you never quite now what you are buying. Just like buying a used car buying dive tank can be a bargain, saving you a considerable amount off a new one or a complete waste of money. CylinderThe first thing to keep in mind is that buying a cylinder out of test (in the UK currently two and half years since it's last date stamp) is much like buying a car without a MOT, it's a greater risk and you cannot use it until it passes again. Here are a few tips if you considering buying a used dive cylinder:
  • Look for external signs of damage. If it has any dents, deep scratches, rust then it is unlikely to pass it's next test. In fact a visual inspection is the first thing a test cylinder will perform on your cylinder when it is put in for a test. Make sure you remove the boot if fitted and inspect for damage.
  • Check the valve has no signs of damage. They are made of brass (covered with chrome) which is quite a soft metal so any impact will be easily noticeable. A dropped cylinder is unlikely to pass it's next test.
  • Cylinders stored with some air pressure inside are less likely to have internal problem you cannot see. When a cylinder is filled the air is purified and the moisture removed. If a cylinder is stored without pressure then fresh air with moisture in it will fill the inside of the tank. This is a real problem with a steel cylinder as air with moisture will promote rust.
  • Make sure the valve opens smoothly. If it is stiff this may indicate it will need a service, costing around £20. If it will not open then be wary. Firstly you can't tell if it has been stored pressurised (see point above). Secondly the valve may need replacement, costing currently up to £50.
An obvious point to make is the newer the cylinder the less problems it is likely to have. Check the markings around the neck for the manufacture date. Avoid non metric valve threads (metric valves have M25 stamped on the neck) as replacement valves or parts for older imperial valves can be very elusive and costly. A used cylinder requiring a test, a valve service and maybe an internal shot blast (to remove internal rust or corrosion) is likely to cost pretty much as much as a brand new cylinder. However if you get lucky and buy a used cylinder in good condition within it's test schedule could save you over £100! For me a used cylinder represents a huge risk, potentially a huge pressurised bomb (a bit dramatic but 232 or 300 bar of pressure is a massive amount of stored energy). I like to know how a cylinder has been looked after from day one. New or used, always treat cylinders with respect and care. You may be amazed to learn steel cylinders are only around 5mm thick and aluminium walls 11mm thick. To view our great range of new cylinders, click here.

1 comment

  • having just completed my equipment specialist course this was quite a big part of it ,cylinders and regs , what i would add is "also be wary of cylinders that have a really good paint job " , as with a car paint can cover all manner off repairs dents etc and its always possible that the cylinder may have been shot or sand blasted which can weaken the walls , it would also be wise to check just inside the neck for cracking and also check that the valve is straight as if not this could be evidence that the cylinder has been dropped and believe me as an engineer i saw a valve assembly shoot the length of a factory and embed itself in a wall ( the cylinder itself can take off like a rocket as well ! — my advice " dont buy second hand unless you really know and trust the seller " always buy new !

    dave armstrong

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