Monthly Archives: February 2016

  • What’s Better? DIN or A-clamp?

    The international A-clamp fitting enabling a regulator to be connected to a tank was once ubiquitous at diving centres 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?

    mikron_blue_yokeAs 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.

    mikron_pink_dinThe 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.)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. din_insertOn 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.apeks_din_yoke_converter

    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 (but NOT in the UK).

    yoke_tankAnother 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 centres in the USA and nearby prefer the more robust A-clamp-only tank valve design.

  • An Intro to Diving Computers

    When we go under pressure, our bodies start to absorb the inert part of the air we breathe, the nitrogen. At normal atmospheric pressure we are saturated with nitrogen but by going underwater breathing compressed air, we allow our bodies to soak up more.

    Provided we stay no longer at depth than a slow ascent to the surface can give time for our bodies to off gas, we experience no problems. If we exceed these ‘no-stop’ times, we need to make stops at points during the ascent to allow our bodies to ‘catch up’ with this process.

    An advanced computer watch A typical computer watch

    All certified divers should know this and nowadays most wear a computer to monitor the potential state of decompression during and after each dive. I say ‘most’ because I have recently heard of cases of individual divers who eschew a computer saying ‘they know how deep and for how long they can stay’. This is very dangerous thinking.

    Of course, many years ago when computers were in their infancy, conservative divers refused to use them, believing a watch and depth-gauge combined with a decompression table was safer. They might have been safe if their watches and depth-gauges were accurate and they were disciplined in their use.

    One way to make leisure diving ‘safer’ in this regard is to breathe a gas with less nitrogen in the mix – nitrox – but it is only safer if you don’t take advantage of the longer no-stop times available. Stay longer and you still soak up just as much nitrogen as you would breathing air for the shorter no-stop time mandated.

    Computer manufacturers try to make things as safe as possible to keep them away from possible litigation. That’s why they build in a few precautions that sometimes casual users fail to comprehend.

    suuntodx_elastomerIf you dive with your computer set in ‘air’ mode, it will not allow you to switch to another mode such as ‘nitrox’ until a sufficient period has passed – usually twenty-four hours. If you want to switch between air and nitrox, it’s important to start off in nitrox mode, setting air as nitrox 21 (which it is).

    For the same reason, if you want to use your computer simply in ‘gauge’ mode, reading only depth and time, it will not be able to calculate your residual nitrogen levels should you wish to then switch to a nitrox or air diving mode, so it will lock you out for a period, up to forty-eight hours if you have been diving deep.

    Diving computers have a sampling rate typically of every 10, 20 or 40 seconds. Normally the 20-second setting is the default setting. During a leisurely dive this is entirely practical but it is not suitable for free-diving.

    Some computers have a mode specifically for free-diving when the sampling rate is much more often, even every second. This is because if you swim down to, say, 20-metres deep, a less frequent sampling rate might make a sample point at ten-metres on the way down and the next at 15-metres on the way up, totally missing the fact that you went to 20-metres in between. So gauge mode is unsuitable for use by free divers. You may need a computer with a ‘free-diving’ mode. Choose a computer that has the modes you require.

    Some of our customers tell us they want to free-dive between scuba dives. Current medical thinking believes this to add a degree of hazard to the activities because the scuba diver’s body will still be loaded with residual nitrogen at this time and that will be recompressed during a breath-hold dive. No computer can calculate for these short bounces while in diving mode because of the aforementioned sampling rates. For this reason, no computer should allow you to switch to free-diving mode while it is still calculating nitrogen levels during a surface interval.

    Some foolish divers will leave their computer to ‘off-gas’ at the surface while they go for a swim, ever tempted to duck-dive below the surface. That is a silly as leaving a computer tied off to a rope at the last decompression stop to ‘offgas’ while the diver climbs back on board. We positively do not recommend this. Nor do we suggest you buy a second instrument and switch between them during a day’s diving. That is the road to decompression illness.

    A diving computer can only monitor the nitrogen loading of your body if it is attached to you while you on-gas and off-gas. Use it properly and it will keep you safe – although, since everyone is physiologically different and the computer’s algorithm was written for a theoretically typical person, no computer manufacturer can guarantee this.

    Always read the instruction manual and be familiar with what you computer displays. Too often people go into decompression status during dives, especially where the water is warm and clear, and fail to understand that this is what their computer is telling them.

    A range of different computer displays at depth A range of different computer displays at depth

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