the guy said he was concerned about the impact with the water damaging his regulator. He's not going fast enough for the water to act like a solid which is the only real situation where there is enough force to damage the regulator. Reactive newtonian state was not the right term, but couldn't think of the right one and am on business travel so exhaustion won over trying to describe it. "normal" would have probably sufficed. Though it has more to do with kinetic energy than changes in viscosity, either way, you can't move fast enough to get water to behave like anything other than normal water and damage the second stage.
Either way, put most any second stage in the water diaphragm down, mouthpiece up and it will freeflow, that's how they are designed. The servo second stages won't do it, so Poseidons, Oceanic Omega/Hollis 500se, etc. Some of the pancake octos won't do it because the diaphragm is rotated 90* up so they are hard to get to freeflow, though more difficult to breathe, think Apeks Egress, Oceanic Slimline etc. Any "normal" looking second stage, if you're sitting at the surface and you put the reg into the water diaphragm down, mouthpiece up should freeflow, doesn't really matter how fast or how slow you go, it is how the regulator is designed to function. Instead of negative pressure on the inside of the inhalation diaphragm to draw it in, you are putting positive pressure on the outside of the diaphragm. Net result is diaphragm pushes the lever down. How much pressure it takes to do this is the cracking pressure set by the service tech, more cracking pressure harder to freeflow/harder to breathe and vice versa because it is the same physics behind it. Best solution is to plug the mouthpiece where the pressure inside of the case will be enough to keep the diaphragm down, or better yet, just flip it mouthpiece down and it will never be a problem. Mouthpiece up for backrolls though
