This assembly is the first stage (G5/8", model 3950, part.no. 3720) of the trusty Poseidon Cyclon 5000 diving regulator. The dimensions are taken quite precisely (+/-0,02mm) from an actual instance, but be aware that they might differ to another one due to manufacturing tolerances. The part names contain the old part numbers from Poseidon, the O-rings also the new part numbers and their metric sizes. The position of the valve piston, the shape of the diaphragm and the length of the springs are depicted in the balanced working position when pressurised with 11,5 bar on the second stage side.