This is timely for me, because I’m putting together an O2 reg and my choices are MK10 and MK2, and I have a MK10+ conversion kit. SP does sell a MK25 ‘nitrox’ rebuild kit with a bright green seat, that would also fit the MK10+ as mentioned. That kit is like $100. I’m way too cheap for that, lol.
Then there’s the discussion about the O2 compatibility of the MK10 vs the MK10+, assuming both are using the standard seat. I’d be interested in knowing the actual material that these seats are made of and thus the ignition temp. I could take a wild guess that they’re roughly the same risk of igniting.
A dive shop owner recently told me that he had heard that the sharp knife edge piston regs are not considered as O2 safe because the thin edge gets hotter as air flows around it. I’m thinking that is absolute B.S. Gas isn’t forced around the piston edge, it expands around the piston edge. In fact, that is the exact site of adiabatic cooling, the coldest spot in the regulator.
So I can’t think of any advantage to using a MK10+ over a standard MK10 other than the availability of the green seat. And…I don’t know what the real, not claimed, advantage to the green seat is. What is it made of, how much more ignition-resistant is it, etc. If it’s simply a matter of the seat holding up to O2 exposure, to me that is no reason to spend $100. I could change the seat out after every single O2 dive for a couple of years and still be ahead money-wise, given how infrequently I’ll use it.
Even though I’m starting to ramble (sorry about that), I wanted to add that I’ve ended up deciding to go with a MK2 for my O2 reg. It has much less combustible material in the HP section, no dynamic o-rings exposed to HP, in fact the only o-rings that see HP in the regulator are the two on the DIN retainer and the single HP port. That’s outstanding. The seat is tiny, and SP does make an O2 compatible seat which is not nearly as expensive as the MK25. The only drawback for my use is that there’s no turret, which means the hose routing is a little less streamlined, but I’ll gladly live with that.
