No offense, but the statement that pistons are "almost always problematic in cold water" is simply not true. Do you have any idea how many cold water dives have been made with piston regulators? All the MK5s and 10s with the SPEC kit, all the sherwoods, all the atomic sealed pistons, and many thousands of cold water dives with the MK25. Just because you've read on SB about MK25 freeze-ups doesn't condemn an entire regulator design.
For absolutely certain, Oceanic states in the User Manual that NONE of their piston regulators are to be used below 50 deg F.
AquaLung waffles a little bit but, in the end, they point out which regulators meet the EU spec for cold water. See the bottom of the page here:
Aqua Lung Regulator Range The two Calypso entries in the table are piston regs but where they show a picture of the reg, there is no icon for cold water use. Apparently, they meet the standard but are not recommended for cold water diving. All of the recommended regs are diaphragm.
Here's what SP has to say:
Cold Water Diving With SCUBAPRO-Diving conditions can be drastically different, including extreme cold water and outside temperatures, posing the possibility of a regulator "freezing". Therefore, resistance to freezing is imperative for the diver. All SCUBAPRO regulator systems are CE approved for 4300psi cold water diving. Some models go even beyond this super stringent qualification and have successfully been tested in extreme cold diving conditions at less than 36°F. As a specific anti-freezing measure, SCUBAPRO engineers have designed a patented finned cap for both the MK17 and the MK25 first stages for optimal cold water diving. The ribs act as a radiator to increase the surface area of heat transfer from the water to warm up the internal parts that have been drastically cooled down by the gas pressure drop. On the MK17, a dry ambient pressure chamber enhances the resistance to real ice cold water at any depth compared to other dry chamber diaphragm first stages. For cold water diving, SCUBAPROÃÔ second stages feature precision molded carbon fiber and technopolymer valve housing and components. They even exceed the CE cold water norm. In addition, these components contribute to their lightweight features and corrosion resistance.
They state that they designed the Mk25 for cold water diving but then don't include it when discussing 'real ice cold water'. They do say that all SP regulators are approved for EU cold water diving. But so is the AL Calypso, an unbalanced piston at the entry level of resort regulators.
There's a reason that Mk25s are discussed on SB in the context of freezing. They have done it before. If people write in and say 'my Mk25 froze' there are two answers: your technique led to the failure or use a Mk17. But, at some point, changing technique won't overcome the problem. The simple solution is to change the first stage. Has anybody ever written in to complain about their Mk17 freezing?
This freezing topic comes up all the time. It is almost always in the context of piston regulators. Sure, pistons have been used for years. And they will continue to be used with or without SPEC kits.
I still consider DA Aquamaster to be the expert in SP regulators. If he is recommending the Mk17 for cold water diving, it's good enough for me. Although, to be honest, I bought the Oceanic Delta 4 for my wife. The next cold water reg I buy will be a Mk17/G250V.
See Post 7 here:
http://www.scubaboard.com/forums/regulators/254603-first-stage-right-me-mk17-mk25.html among many similar posts re: the Mk25 versus the Mk17.
Or just search for Mk 17 or Mk25. This comes up all the time.
Richard
