The international A-clamp fitting enabling a regulator to be connected to a tank was once ubiquitous at diving centers worldwide, but recently the German DIN fitting appears to becoming more popular. When it comes to buying a new regulator, the choice is yours but which is best?
As usual there will be those that show unswerving loyalty to one type or the other and robustly defend their choice, but the truth is that both systems have advantages and disadvantages.
The A-clamp uses an O-ring fitted to the tank and the regulator is clamped to it. These O-rings can get damaged in normal use especially in a busy tank rental situation so it’s a very good idea to inspect it before you connect up and go diving. Wise divers carry a few spares just in case and are aware in different parts of the world these O-rings can vary slightly in size. However, a good O-ring combined with a properly mounted regulator first-stage can give trouble-free service for the ordinary single-tank diver. That said, you’d often see divers with fine bubbles escaping from the interface between regulator and tank valve thanks to a worn tank O-ring.
You’ll also hear stories of A-clamps coming mysteriously undone. It’s an urban myth. Once the tank valve is open the internal gas pressure makes it impossible to disconnect just as with a DIN valve.
The regulator with a DIN fitting carries its own captive O-ring. These too can wear but, not subject to the vagaries of many different size regulators being hooked up to them, they wear a lot less than the easily replaceable O-ring on a standard A-clamp tank.
Not only that but without the complexity of the clamp, the DIN regulator has a lot less metal and is on consequence lighter. It is screwed directly into the thread of the DIN tank valve where the O-ring makes contact internally at the back. On the face of it, the DIN fitting is a better solution.
Part of what is driving the popularity of DIN-fitting regulators is technical diving. When using a cluster of tanks, a cluster of A-clamps can be an entanglement issue. Not only that but you can get DIN tanks and suitable regulators with longer threaded section to be used with much higher tank pressures than 3000psi, providing more gas in a similar size tank. (Be aware you cannot use a standard DIN connection in one of these high-pressure tank valves although you can use a high-pressure DIN fitting regulator on a standard DIN tank.)
Most DIN fitting tanks at dive centers outside the American sphere of influence have a little slug that can be inserted so that they can be used with most A-clamp fitting regulators as well. Clever divers always carry one of these slugs with them if they have an A-clamp regulator but where DIN tank valves are more popular. On the other hand, many dive centers in the USA and Caribbean areas often only have standard A-clamp tanks so that those with DIN regulators must fit a bulky A-clamp adaptor, something that pushes the regulator a little further forward and can prove uncomfortable at the back of the head.
There are a couple of disadvantages of the DIN system, which exponents tend to gloss over. Firstly, those with weaker fingers find them difficult to screw up tightly or unscrew especially if hands are cold or the diver has long manicured nails. Be aware too that regulations in Europe stipulate that nitrox tanks and regulators require a different DIN thread size to that of tanks intended for use with air. Another is that tank valves are usually of brass and if rough handling deforms the tank valve even slightly, it can prove impossible to fit a regulator. That’s probably why busy dive centers in the USA and nearby prefer the more robust A-clamp-only tank valve design.