Hmm. Rookie but I'll try to explain it clearly. Imagine a tube open at one end with two holes drilled on opposite sides. Stick this inside another tube just like it thats just a little bigger so they nest. Attach your breathing hoses and one way valves(mushrooms) to the openings in the side of the outer tube and put a mouthpiece at the open end. Now you have a DSV. Drill a hole 90 degrees away from the others in the outer tube and attach a OC second stage and you have a DSV with OC Bailout. By turning the inner tube 90 degrees you line up one of its two holes with the hole to the OC reg. The holes in the inner tube no longer line up to the holes in the outer tube so your Rebreather loop is closed completely.
I hope this makes sense
