We tested a Scubapro Mk 17 on some long, deep, silty and cold dives (low 40's) over the weekend and based on it's perfromance under very demanding conditions, I have ordered two of them to replace my Mk 20's. It is about the same size as the Mk 16, which makes it very compact for a high performance first stage and the hose routing of both the Mk 16 and Mk 17 is very Poseidenish with it being very easy to rout everything straight down.
The Mk 17 is also fully sealed which eliminates the only real advantage Apex had over the Mk 16 or Mk 20/25. So in short, I have no reservations in recommending it for a technical diver.
As for second stage criteria, getting one that can be dissasembled underwater without tools is absolutley the last criteria on my list. It's one of those ideas that sounds pretty good until you think about it.
Disassembling a second stage to remove rocks, sand, etc, might work in a non silted non flowing cave (probably an oxymoron) where you could work on the reg while lying on the bottom, but in any kind of flow, in open water, or in a current in a current the job gets progressively harder with an exponetially increasing potential to lose parts. Once you get to the point of trying to do it in 35-40 degree water in dry gloves or heavy neoprene gloves with cold hands while hanging on an ascent line in a current, taking the second stage apart to fix it is not a viable option.
A far better option would be finger tight second stages and matched IP's so that you could swap out a malfunctioning second stage with one not currently in use. That is do-able in cold water with gloves and in a current. And besides, anything that got in the second stage came through the mouthpiece and in most cases you can shake it back out the mouthpiece.
So in short, pick a second stage that breathes well, breathes dry and is in general pretty durable and reliable. A simple downstream poppet designed second stage like a Scubapro R190 or R290/380/390 or Aqualung aquarius or Conshelf whatever can be made to breathe well and are really simple and bullet proof. Balanced regulators tend to breathe better and tolerate IP changes better, while regulators with spring adjustment knobs can be adjusted to accommodate normal seat wear over the course of a season without giving up performance. How many of the above features you want is a personal choice. Frankly, I have seen very few upper end second stages from major maufacturers that would not serve well in most technical situations.
The Mk 17 is also fully sealed which eliminates the only real advantage Apex had over the Mk 16 or Mk 20/25. So in short, I have no reservations in recommending it for a technical diver.
As for second stage criteria, getting one that can be dissasembled underwater without tools is absolutley the last criteria on my list. It's one of those ideas that sounds pretty good until you think about it.
Disassembling a second stage to remove rocks, sand, etc, might work in a non silted non flowing cave (probably an oxymoron) where you could work on the reg while lying on the bottom, but in any kind of flow, in open water, or in a current in a current the job gets progressively harder with an exponetially increasing potential to lose parts. Once you get to the point of trying to do it in 35-40 degree water in dry gloves or heavy neoprene gloves with cold hands while hanging on an ascent line in a current, taking the second stage apart to fix it is not a viable option.
A far better option would be finger tight second stages and matched IP's so that you could swap out a malfunctioning second stage with one not currently in use. That is do-able in cold water with gloves and in a current. And besides, anything that got in the second stage came through the mouthpiece and in most cases you can shake it back out the mouthpiece.
So in short, pick a second stage that breathes well, breathes dry and is in general pretty durable and reliable. A simple downstream poppet designed second stage like a Scubapro R190 or R290/380/390 or Aqualung aquarius or Conshelf whatever can be made to breathe well and are really simple and bullet proof. Balanced regulators tend to breathe better and tolerate IP changes better, while regulators with spring adjustment knobs can be adjusted to accommodate normal seat wear over the course of a season without giving up performance. How many of the above features you want is a personal choice. Frankly, I have seen very few upper end second stages from major maufacturers that would not serve well in most technical situations.
