So you want to buy used scuba tanks, but you aren't sure what to get.
Aluminum SCUBA Tanks
First off, I would not buy any scuba tanks that do not have a current visual inspection or hydrostatic test, unless they are really cheap, and I mean really cheap. We charge $8 for a visual inspection and $35-40 for a hydrostatic test. I would not pay more than $5 for a that does not have a current Visual Eddy Test. Why $5?
That is the scrap metal value for an aluminum 80 when it fails. 6351 aluminum cylinders are all Walter Kidde tanks and tanks made by Luxfer prior to 1988 (it varies from year to year by the size of the cylinder).
Look at the DOT numbers. Are they X’d out? If so, the cylinder has been condemned.
Is there air in the cylinder?
Is the paint flaking or bubbling?
Are there dents pits or gouges?
Does it have a boot? If so, look under the boot.
Does the valve turn easily? A valve rebuild is about $20.
Steel SCUBA Tanks
Does it have a current hydrostatic test and visual inspection?
Is there rust anywhere on the outside? Once rust starts it is hard and difficult to kill.
Does it have a boot? If so, remove it, rust loves to hide under tank boots.
While you have the boot off, pick up the tank by the valve and strike the cylinder with a hammer or wrench. It should have a bell like sound. If it goes thunk that is a sign of rust or water inside of the cylinder.
Are the DOT numbers deep and legible? Shallow or smooth numbers are an indication the cylinder has lost quite a bit of metal.
Has it been repainted and can you see the DOT numbers? If you can't see the DOT numbers it will not pass visual inspection or a hydrostatic test until the paint has been removed to be able to see the numbers.
If all else fails you can always call Kona Hydrostatic Testing and we can answer any tank questions for you.