When buying a used scuba tank (aka: cylinder or bottle)...whether online from eBay or Craigslist, or from a Garage Sale or Swap Meet/Flea Market...be sure to consider the following:

Does the air tank need a hydro?
Check out the markings on the scuba tank to determine if the most recent hydrostatic pressure test date is within the last 5 years. You are taking a risk in buying a tank that needs hydro. Consider the cost of a hydro inspection ($25-$40) when negotiating the purchase price. Ask the seller for a written guarantee to refund your money, and possibly the cost of the inspection, if the tank fails hydro.

Does the tank have air in it?
If the tank does not currently have air in it...moisture could have gotten in, which would cause rust or corrosion. It is not recommended that you buy a used scuba tank that does not currently have air. You can ask the seller to use a pressure gauge to measure the amount of air in the tank...or slightly open the tank valve and listen for rushing air.

If aluminum, is the tank older than 1990?
Before 1990, some manufactures (mainly Luxfer and Walter Kiddy...not Catalina) used a certain aluminum alloy (6351) that increases the likelihood of cracking. An Eddy-Current test ($20-$30) is required on these tanks.

If steel, does the tank have a spray-in liner or coating on the inside?
On older steel tanks (usually 72 cu/ft), manufactures sometimes sprayed a coating on the inside (color varies, but usually light cream, dark red or white). This coating can conceal defects, and over time the coating itself can deteriorate. The tank can be tumbled to remove the liner, but after tumbling the tank will require maintenance more often which increases the cost.

Here are some tips on inspecting a used scuba tank:

- Look for external signs of damage. If it has any dents, deep scratches or rust, then it is unlikely to pass inspection. If applicable, remove the boot on the bottom of the tank and inspect for damage.

- Check the valve for signs of damage. They are made of brass (covered with chrome) which is a soft metal, so any impact will be easily noticeable. A dropped cylinder is unlikely to pass inspection.

- Make sure the valve opens smoothly. If it is stiff, service may be required, costing around $25. If it will not open, then you won’t be able to determine if the tank has air...and the valve may need to be replaced, costing around $60.

Scrap metal value of scuba tanks:

A standard aluminum 80 cu/ft tank weighs about 31 lbs empty. At current rates, scrap aluminum is worth about $0.75 per lb. So the current minimum value of an aluminum scuba tank (without the tank valve) is around $23.

A standard steel 80 cu/ft tank weighs about 35 lbs empty. At current rates, scrap steel is worth about $0.17 per lb. So the current minimum value of a steel scuba tank (without the tank valve) is around $6.

External Resources:
Scuba Tank Services - Buying Used Scuba Tanks
DiveBuddy Forum Discussing this Topic
A Consumer’s Guide to Scuba Tanks
How to Buy a Used Scuba Tank
How to Read Scuba Tank Markings
How to Select a Scuba Tank
Aluminum vs. Steel Scuba Cylinders

Comments

John_giu - 8/26/2014 7:15 AM I have saved $ buying refurbished tanks from my LDS > northeastscubasupply.com/used-tanks/ They are nitrox clean with rebuilt valves. A garage sale or Craigs list tank might get you a tank that cost more to refurb, than it’s worth

Hawkeye54 - 7/30/2014 10:41 AM I buy used tanks all the time, at fractions of what they cost new. Nothing wrong with them as long as they don’t show signs of abuse or heavy corrosion. Most will be out of Hydro so factor a test into your overall cost. I have yet to have a single one fail hydro, and have only failed one on visual for damaged neck threads. The valves are often in mediocre to poor shape after sitting but for about $15 you can refurbish the guts or for $40-$50 buy a brand new one. Used valves in decent shape are floating all around eBay. My bottom line: Used tanks are a great economical value as long as you don’t buy rust buckets! :)

Smithsgold - 7/21/2014 8:49 PM Thanks Greg I enjoyed the Article !!!

Green_Achers - 7/18/2014 6:50 PM Thanks. I have considered buying tanks many times.

PhatD1ver - 7/16/2014 7:59 PM great post, I might suggest that you add a little on the ’economics’ of the steel tank v AL80... I’ve read a couple different blogs that offer some significant evidence that the diving community has been sold a bill of goods with the AL80... it is a great recreational tank for ’shallow’ rec divers, but a steel 90 has benefits that few shops will teach a buyer about... "An AL-80 has 4.4 pounds of positive buoyancy when empty. Meanwhile a XS-80 Cylinder (xs-scuba formerly worthington) will be 3 pounds negative when empty. 4.4+3 = 7.3 pounds of difference in buoyancy. The aluminum tank is a liability since you need to add weight to hold it down at the end of the dive. The steel tank contributes to keeping you and your exposure suit down. The 7.3 pounds represents 7.3 pounds of weight you do not need to wear when diving a X-80. This comes right off your belt. Now when you go to walk across the beach... A Luxfur 80 weighs 31.4 empty less the valve so add about 2 LB for a typical valve = 33.4 pounds A xs-80 weighs 27.7 pounds empty including the valve. Again both are filled with approximately the same air volume. So since 33.4 - 27.7 = 5.7 the aluminum 80 is 5.7 pounds heavier on land. Also remember the AL-80 diver gets short sheeted with only 77.4 CF in a nominal fill but that’s trivial in terms of weight. The XS-80 filled to 3442 PSI hold 81 cubic feet of breathing gas. That difference in capacity approaches 5% ! So now the AL-80 diver has a tank that’s 5.7 pounds heavier and he’s (or she’s) wearing 7.3 pounds of extra weight making him 13 pounds heavier hiking across the beach. He also has that much more mass he’s pushing through the water, Newton’s Laws do apply to divers. Challenging Newtons’ Laws consumes energy and that serves to deplete your air supply faster, shortening your dive." (from SCUBA Knowtes) So, that’s some important information for most divers. Who doesn’t want to shed weights?

flaski - 7/15/2014 9:24 PM If looking for a steel tank, don’t buy used unless from close friend. A new Fabar HP80cu delivered to your door is 245 or less, a 100 is 300. with boot and din/yoke valve included. They will last you 20 plus years. So don’t waste time or money on used tanks. If aluminum 80s are your thing don’t buy used if more then one hydro, so 5 to 6 years old max with a current hydro and vip and only if max of 80.00 any more your better off buying new. I look at it this way "its life safety items, do you really want to cut corners" I have 2 100cu steels and a 120 steel. I am good with air use but would rather come up with a 1000psi left then hauling a pony or worrying about air. My advice is from a 31 plus year diver, 10,000 plus dives, current insured padipro, naui, and loads of other certs.

Eric_R - 7/15/2014 3:20 PM This will be a great resource for divers. Now they can come to one location and get all the info they need.