REGULATOR Scubapro MK25AF/S600
Philosophies on how to go about designing a regulator that will resist free-flow due to icing are diametrically opposed.
     Most regulator manufacturers say that you should keep the working parts of the first stage dry and well-protected, yet some others say that you should get as much water in contact with and flowing past the moving parts as you can.
     Its easy to understand the reasoning of the majority. The others suggest that we should consider the properties of water, because the main body of water in which we dive cannot ever be frozen. It must be warmer than that or it would be solid. So if this water is not frozen, it must have some heat in it, and why not use that heat to keep the regulators moving parts warm
     Warmth and cold are relative terms. The very cold water in which you might dive is certainly warmer than the depressurised air you breathe from your tank.
     So even if the water is at only 3 or 4ÂC, it can be used to keep the regulator from being chilled by its own airflow and above zero, the temperature at which fresh water turns to ice.
     Scubapro is of this second persuasion. For example, its newly designed MK25AF piston-type first stage has enlarged flow holes to facilitate that increased water flow through it.
     The company has also backed its launch with an extensive coldwater-diving advertising campaign. So will it freeze
     I dont know, but I can tell you that it was taken for a swim under water round Wraysbury Lake in early February by Gerry Gooch (see the Drysuit Test in this issue), and he tells me that the water was at a sweltering 4Â above freezing.
     The regulator certainly didnt freeze up on him. Not fully convinced, the next day I asked George Buxton to swim it round the same lake. It didnt freeze up on him either.
     Next I asked Tim Bradley to do the same. The effect was the same, even though this time he intentionally breathed off it heavily in the air before descending and gave it some very heavy inhalations to get as big a flow-through of air as possible, two approaches which are certainly the wrong thing to do in cold freshwater conditions.
     Of course, all my guinea-pig divers had the option of an alternative regulator on the H-valve of the tank in case the MK25AF/ S600 let them down.
     It didnt freeze up. But then neither did the Mares Abyss, the Poseidon Cyklon or the Apeks TX40 regulator being used by the other divers alongside it.
     What does all this prove Nothing really. No-one can anticipate when the conditions within a regulators moving parts are right for a free-flow due to freezing. We can only do our best to avoid the circumstances that might lead towards the event.
     The fact that the Scubapro MK25AF/S600 didnt fail probably means that it has a good design that will help avoid that happening. I cant guarantee that one will not freeze up on you, but I can say that it is less likely than with some other regulators.
     I can make no guarantees, because you never know how close you come to the edge of disaster until you are beyond it. I cant tell which if any of the regulators in use at Wraysbury on those days was close to freezing.
     Its very hard to test for internal icing. Purging regulators continuously while they are submerged in a bucket of ice water provs only that any regulator will freeze up if you try hard enough, and purging a regulator while diving in cold fresh water is simply asking for trouble. You should avoid big airflows.
     Scubapro has done its best to improve the coldwater performance of an otherwise very high-performing and well-thought-of regulator. If you intend to dive in very cold fresh water, it is worth considering.
     However, from my observations of experienced ice divers and my comparison of many less-than-experienced divers I see going diving in cold fresh water, I would say that the most important thing is to learn the techniques to suit the conditions.
     The Scubapro MK25AF/S600 has the now-familiar revolving turret first stage with two high-pressure and five medium-pressure ports. Apart from the enlarged flow holes, a series of heat-exchanging fins are obviously a new feature. These are also said to help prevent any ice that might form creeping up towards the turret.
     Out of view, the internal mechanism has a polyurethane-coated spring and a mirror-polish to the piston shaft to deter ice from sticking. The piston itself has a composite end that prevents heat being drawn from the spring.
     The second stage is of a mainly plastic construction with a dive/pre-dive venturi control and a breathing-resistance adjustment knob. Scubapro recommends removing the hose protector from the mp hose, where it joins the second stage, to help heat transfer in cold conditions. It has an easily unclipped-for-replacement mouthpiece.
The Scubapro MK25AF/S600 costs £349.
  • Scubapro UK 01256 812636, www.scubapro.co.uk

  • Divernet Divernet
    + Now good for use in cold fresh water

    - None encountered