Sorry mate you are well off course here,
do not dive a mccr with a depth compensating stage !!!!! This does only work for a scr NOT mCCR.
As your upstream pressure increase your o2 output increases as well which will make your loop hyperoxic at depth. THIS IS VERY DANGEROUS. If you than have only one first stage the only thing you can do is turn the supply off and drive the unit home by using the tank valve - not an easy task.
You either use one 1st stage non-depth-compensated as does the rEvo II hybrid. Howver you have to change the systems to eCCR only if you plan to go deeper than i think 80 meters ( Paul correct me if i am wrong).
Another way is to use 2 o2 tanks with 2 1st stages, one feeding the mCCR and one feeding the eCCR.
Good thing here is that a)you dont have to worry so much about the max depth of the mCCR,
b) you can run the mCCR at an ideal IP as well as you can run the ideal IP for the eCCR ( e.g. Inspo wants 7-8 bar ip for the solenoide, mCCr want 10-13 bar)
bad with that is that you will have a) offboard o2 which will make the unit larger - might be a squeeze in some wrecks afterwards
b) you have to maintain 2 1st stages
good thing - if you had an idsependent monitoring such as diamond HUD (
www.rebreathersolutions.com - I think-), rEvo dream ( Paul ) or the shearwater HUD, your systems becomes double redundant. If you even throw extra o2 cells in your are redundant except for your scrubber.
good people to talk to are ( in no particular order :-) )
a) John - narked@90
b) martin - tecme.de
c) Paul - he does the rEvo - dont know the website by heart - check the net or PM him he is on this forum as well
but these are only my .02
this system sounds like it would work, but like i said since i know my max depth i could easily just get an orifice (or lock a needle valve to the right size) that is the right size so its max out put, at my max depth, is just below my metabolic rate. Unless i keep adding o2 manually at the same rate as i would have too at shallower depths there shouldnt be a risk of hypoxia, right? unless of course I go deeper than I am planned on which shouldnt be an issue since ill just set the orifice to my max training depth.
Im pretty sure there are units that use this method, and im pretty sure Ive, read about a few home builds that use this method. Ill have to look the threads up again, but i think Dave Sutton has posted on a Mccr that uses a depth compensating first stage and an orifice, and you just use the right orifice for the right depth, then just add more frequently when you are shallower to maintain your po2.
-Alex (the one guy stupid enough to give up his spot for OC trimix to save up for a rebreather)