There is no manual. On Facebook on the European side, there are some exploded diagrams by Kieran. More like what you are looking for would be this video on Vimeo:
It is done by Wayne Fisch at RebreathersUSA.com and authorized by Jan at JJ-CCR in Denmark. That said, some of the technique used for oring removal with screwdrivers is a bit cringeworthy. The part where the DSV is disassembled is at the 15 minute mark, but I don't remember that they changed mushroom valves.
To do that, fold the valve in half and holding as close as you can to the center stem, pull it out of the wagon wheel. It will come loose without tearing. Note that you can't replace the same valve because after clipping the center stem short at the barb, there's nothing left to grasp. To replace a new valve, thread the stem in and seat it by pulling with your fingers. Using forceps will tear the stem. Then snip it off just past the barb.
Take pics with your phone beforehand! You don't want to reassemble with the valve on the wrong side, though the assembly shape tends to keep you from doing that.
Follow the video for replacing the orings. You might want to consider putting the center oring around the mouthpiece in its land dry. Then add your silicone to the barrel afterward. If you lube that one before insertion, it will tend to ooze out of position as you slide the outer sleeve back over the barrel. Adding the silicone to the top surface afterwards works much better.
