More on buying used scuba tanks – beyond the visual inspections!

This is my second installment on buying a used scuba tank. This blog I am going to discuss sizes, capacity, buoyancydurability, and price considerations when choosing the right scuba tank. If you are boat diving, you will find that most dive operators supplying your tank carry the standard aluminum “S80”. The S80 is the “go to” tank for many dive companies because it is cheap, probably the cheapest and most prevalent tank on the market currently. And they are buying in bulk.

But, you are likely not buying in bulk. There are a plethora of sizes, shapes, and air capacities to choose from when you are buying your own. Here are some things to consider as you narrow down to the tank style you want.

Look at size: How big, or small, should you go…and why? Is length an issue, or width? The main considerations is your body size. Obviously, if you are a taller individual, the length of the tank will be less of an issue. But shorter statured folks may find a longer tank interferes with overall lower body maneuverability at depth, sitting on the bench while prepping donning a BCD may be impossible, and walking the tank without dragging along the ground is out of the question. The average aluminum S80 is about 26 inches long, which may be too much length. There are companies that make 80’s that are 3 inches shorter, and slightly wider. You can find tanks with a lesser air capacity for around 22 inches. There are stainless S80’s that shorten the length all the way up to 20 inches. The average diver is 5ft 9in tall. The average human trunk on this 5ft 9in individual (from lower neck to tailbone) measures 26in in length. So you can see, anyone less than 5ft 10in is probably feeling their tank on the base of their skull or back of their thigh on occasion.

Look at air capacity: Naturally, more compressed air means a longer dive. But, when is big just too big? More air is better, of course, but you’ve got to have an intelligent balance between capacity, physical size, weight, and buoyancy. To confuse the issue further, there is a difference between a tank’s volume (capacity of cubic feet of air the tank will hold) and the tank’s pressure tolerance (the amount of air pressure the tank can withstand against the walls without rupturing). Bottom line: yes, there is such a thing as a tank that’s too big.

You can find can find tanks with air capacities from 63cuft (smaller tanks are available for rescue and backup purposes) all the way up to 130cuft. And, you can find LP (low pressure tanks) with PSI of <3000, up thru HP (high pressure tanks) with PSI of 4400. You can put higher pressures of gas into steel tanks. Meaning a steel tank can carry more air and be lighter than its aluminum counterpart. Confused, yes? So, my advice would be to look at the diving you will be doing the most. If you will be doing shore diving in warmer climates, you may want a larger air capacity. You can stay down longer. If you are diving a cold water shore dive, you may be too cold to go on with a dive long before you blow thru 4400 PSI.

Look at buoyancy: Weight is important at the outset of your dive, but it becomes a bigger issue as your dive progresses. As you use the air in your tank, the weight of your tank changes. As the tank weight changes, so does your overall weight and trim at depth. For example, an aluminum tank tends to float “tail-up” towards the end of the dive, changing your trim and making your feet point up. And, you could lose enough weight to make it difficult to control your ascent. Tank weight also makes a difference when lugging your gear to and from the dive.

An aluminum S80 might weigh 33lbs, and it may have a 4lb positive buoyancy when empty. You will have to accommodate in extra weight at the start of your dive, for that 4lb pull toward the surface at the end of your dive. A steel tank on the other hand, might have a published weight of 31.5lbs, and be 6.5lbs negatively buoyant when empty. So while the published weight of the aluminum tank is greater, the diving weight is actually much less. I have to say, I dive with steel tanks. I use the weight of the tank to my advantage when diving. I would rather add air to my BCD at depth to maintain neutral buoyancy, than risk difficulty staying at depth, or worse an unplanned ascent.

Look at durability: Aluminum tanks have had issues with cracking in the past. They both can dent and/or deform with improper handling or storage. See below on the “Eddy-Current” test in that regard. Aluminum tanks also have the ability to oxidize. And, steel tanks rust, which is a more serious problem to be sure. But, these issues should be addressed appropriately with the hydro, vis, and burst disk, inspections which should be done (or current) on any tank you buy. There is essentially no difference in longevity between aluminum and steel tanks if properly stored and cared for.

Last, and possibly most important, is a look at price: All tanks, aluminum and steel, new and used, can put a dent in your wallet. Used offer less of a dent. I am a fan of buying used tanks for just that reason. Well cared for pre-owned tanks have a long life, 20-30yrs or more! You will find that aluminum tanks are almost half the price of steel tanks. And, HP tanks are more expensive thank LP tanks. And of course, valves can alter the price as well (another blog subject I think). A reputable seller will gladly educate you and answer questions, as well as offer up appropriate paperwork without you needing to ask. BlueOrbDiving.com will answer questions and give you free estimates if you can email them pics and information. Google.com is always good for the general question. And, a good dive shop may be helpful (or they may steer you toward that new tank buy with all sorts of used tank purchase horror stories too!).

When you finally decide what type, size, and PSI tank you want, give the previous blog a read. You can also check out a blog on buying used scuba gear. There are some important inspection and safety items you will need to address before you write the check. There are also some important storage and maintenance tips as well.

More on the “Eddy-Current test”: This is a test with an electronic device used to detect micro-cracks in neck of a certain type of tank made near and before the 1990’s. This is done IN ADDITION to a visual inspection on older tanks, with an additional fee. The jury is out on the necessity of this test. Some claim many tanks are wrongfully condemned by the test, or shop owners are being greedy. Some argue you can never be too careful with life-support equipment, the test is valid, dive shops can be incompetent or make mistakes, and lives are saved. In the end the choice to pay for the additional testing lay with your comfort level.

Buying a scuba tank is a great way to save money, recycle the metal, and gear yourself up for more diving. And, you remove the hassle and extra cost of rentals. I hope the information presented has been helpful as you search for that used tank to add to your total dive system. If you have questions please feel free to email me.

Authored by Lisa J Henry

“Be the sea”