Part 3 – did you check out the valve on that tank? Buying used scuba tanks.
As promised, this is the follow up on the 2 blogs about buying used scuba tanks. What do you look for in the tank valve, when buying a used scuba tank?
In the first blog in this series, I discussed things to look for when buying a tank. As part of that discussion I briefly touched on assessing the tank valve as part of the general pre-purchase inspection. The second blog went into details about the assessment of used tanks. This blog will go into some additional detail with regard to types of valves, how they function, and what to look for before you purchase the tank.
The purpose of the tank valve is to release the air compressed in the scuba tank in a controlled manner. In other words, it switches the air flow either on or off. Valves are available in several styles. These are the “K” valve, “J valve”, “H valve”, and the “Y valve”. They have a “yoke” or “DIN” attachment for the first stage regulator.
“K valves”- are the simplest and most common of the scuba diving tank valves. They are currently found on most tanks, and have “yoke” attachments. The O-ring on the valve expands with air pressure, creating a seal between the regulator and the valve. Thus the importance, as mentioned in previous blogs, of a close inspection of that O-ring when purchasing a used tank.
“J valves”- are similar to K valve. The J valve, however, has an the addition of a small mechanical arm that moves in a vertical fashion. The small arm is attached to a rod that runs the length of the tank. This is a reserve lever, and is now an obsolescent feature on the standard tank. The reserve lever functioned to allow access to an extra 300 – 500 PSI of reserve air within the tank near the end of a dive. This served as a safety feature until pressure gauges came into common use. To tap into the reserve air a diver simply pulled down on the rod, in turn pulling down the small lever arm on the valve. Pulling down the lever would allow access to the remaining 300 – 500 PSI of air, thus allowing the diver safely to surface. Unfortunately, if the reserve lever was inadvertently triggered during prep or entry, when the diver pulled the lever, having already activated, there was no reserve…a dangerous thing. Divers that scuba in zero visibility can still use the valve when the gauges can’t be read. Otherwise you rarely see them in use.
“Y valves”- with a valve body split into two posts, and shaped like a Y, allowing for dual systems and redundancy in technical diving. The “H valve”- is adapted from the Y valve dual outlet setup. The H adapter screws into the crossbar outlet of the K valve, allowing a second regulator to be attached. It looks like an H. This is a redundancy used in a technical diving setup in the event of a regulator or hose failure.
The Y and H valves are similar in function and nature with the only main difference being the shape of the valves. There are also other types of valves such as the J valve and in the past, the R valve, but these valves are no longer used widely as they pose a safety threat to the diver when not handled properly.
The attachments for fitting the first stage regulator can be either “Yoke” or “DIN”.
A yoke regulator, is also called a A-Clamp regulator. The “yoke” is a metal oblong fitting that slides overtop of the valve on the tank. The regulator is locked into place with a large screw, which tightens it to the valve. It is very common in the USA.
A DIN (Deutsche Industrie Norm) fitting attaches the first stage regulator with a threaded post. The threaded post on the first stage regulator screws into the tank valve. There is no additional fitting. The O-ring is placed differently than in a yoke. Thus the O-ring is placed behind the post, and not squished into place by pressure. This prevents extrusion of the O-ring, thus preventing leaks at depth. It is called a “captured” O-ring, and is more common outside of the USA.
To add to the madness, there are two different kinds of DIN regulators/valves: a larger and a smaller PSI (or BAR). They are different sizes and require longer or shorter posts with more or less threads. The 300 bar valves require a longer post and more threads. The choice lies in the pressure the tank valve is rated for. A 300 bar DIN regulator can be used on a 200 bar valve, but a 200 bar regulator will not seal properly to a 300 bar valve. It makes little sense to buy a 200 bar regulator, when the 300 bar fits all. Otherwise, there is little difference as far as the regulator is concerned. When you are purchasing a used scuba tank, you will want to be sure you match your yoke or DIN regulator to the valve on the tank. You should also check the pressure on the tank by looking on the neck of the valve. The pressure in the tank should never exceed the tolerance listed on the valve, ever. Additionally, there are adapters than can be used to convert a yoke to a DIN, and visa-versa. If you need your rig to do everything, go with a 300 Bar DIN regulator, and a DIN to Yoke adaptor.
If you are not buying a system you are familiar with, or if you are trying to get a yoke matched up to a DIN, you should probably run it buy your local dive shop for safety’s sake. Again, when it comes to the life support equipment in your total dive system, you can never be too safe.
Last thing I want to discuss is a nifty valve made by XS Scuba called the “Modular Pro Valve”. What I like about the valve is this: The valve has a unique hand wheel that is bicolored, allowing the diver to see visually if the valve is off, on, or somewhere in-between. There are a set of green and red rings on the wheel near the valve stem. As you turn the wheel to open or close the valve, the color on the wheel changes with you. So, a closed valve is red, and an open one is green. In-between open and closed will show both red and green. This is a great little plus on your valve. Pro Valves are available for cylinder pressures of 2400 psi (165 bars), 3000 psi (200 bars), and up to 3442 psi (240 bars). Safety first!
This is the last of the 3 part blog on buying used scuba tanks. Now you are an old pro! Go forth and dive…
Authored by Lisa J Henry
“Be the sea”