halocline
Contributor
I must not have been clear. The atomics, like most other high performance barrel poppet 2nd stages, use a balance chamber to divert IP and use it as a spring assistance. I did not mean to imply that they're not balanced 2nd stages. However, in the SP S600 and later G250HP, there is an additional balance chamber (I guess it's called the 'anti-set chamber' in the G250 HP guide) that is in line with the actual poppet balance chamber. Sort of a 'floating' balance chamber I guess. This removes tension from the mechanical spring pressing the seat against the orifice when the reg is not pressurized, but is not designed to actually remove contact between seat and orifice.
The atomic uses a spring cup washer to physically move the orifice off the seat when the reg is not pressurized. This is why you can't soak the reg un pressurized. To me that would be a deal breaker; but that's just my personal opinion.
The 2 year service interval, while certainly influenced by the seat saver, is actually more just a move by atomic that is ahead of its time. Virtually ANY decent regulator that is cared for correctly can go at least two years between servicing, given normal recreational use, say 100 dives or less in the two year period. Atomic seems to be one of the only manufacturers to be smart enough to recognize it publicly. I believe that the entire industry model of required annual service is on the way out.
Another thing about 2nd stage seat wear; SP switched to a plastic orifice at some point with a more rounded edge, and although that does make tuning more of a crapshoot, it does reduce seat imprinting over the long haul. I have a friend with an old G250 that came with a plastic orifice (no doubt installed at a previous service) and I've seen it after a couple of seasons, with a barely noticeable set on the seat. Certainly nothing that would require a rebuild.
