Herman wrote:Same thing, your IP is 14.7psi....at the surface anyway.
That is very true when the valve is closed, like when you are exhaling.
But during inhalation the gas dynamics get a bit more complicated. Even do these regulators have a single mechanical stage, they actually have two very discrete pressure drop points where pressure discontinuities form (actually pressure drop planes). These sudden pressure drops actually form supersonic shock waves in the regulator at the pressure drop planes.
In these single stage regulators, the first pressure drop occurs (as expected) at the valve, in the orifice. The second actually occurs at the venturi nozzle (or the exit from the pressure body into the can/ horn).
There is a small dynamic pressure chamber surrounding the push pin. The boundaries are from by the valve (supplying the gas pressure), the O-ring around the pin (sealing), the venturi nozzle and the other bleed ports (bleeding the pressure).
I call it a dynamic pressure chamber, because the pressure only builds up during dynamic flow.
I have measured the pressure inside the chamber and when taking a breath the pressure fluctuates depending on the amount of inhalation. The more inhalation, the higher the pressure. With a very deep breath I have seen it reach 180 psi, but on average it normally only goes up to somewhere between 70 and 120 psi.