that was me... thank you thank you, bowing..
I'm glad I posted it, now I know I need a new environmental seal as it actually touches the inner plunger when depressurized and even partially when pressurized as it seems the membrane has become too elastic.
This is normal.
It HAS to touch the inner plunger in order to transfer water pressure from outside the reg to the spring pad seated on top of the diaphragm. Look at it another way.
The volume of the ambient chamber is fixed and the pressure outside it and inside it a the
surface is 1 atmosphere (ATM).
At 33 ft the water pressure is twice as high (2 ATM) but the pressure of the air inside the ambient chamber is still the same old 1 ATM as it is fully sealed so nothing gets in or out. This means there is a 14.7 psi presure differential across the external diaphragm.
At 231 ft the pressure outside will be 8 times as great (8 ATM) but the pressure inside is still for all practical purposes the same as at the surface (1 ATM). What the means is that at 198 ft the pressure difference is now 103 psi across the external diaphragm.
If you notice what is under the daiphragm you'll note that it cannot move too far inward before it is resting on something. This ensures two things:
1) The pressure is transferred to something mechanically (in this case by pressing against the plastic transmitter piece that runs through the spring and contacts the spring pad.
2) The diapragm only moves a small amount inward until it is resting on either the transmitter or the body of the reg, ensuring it does not bulge too far inward and rupture.
In a dry sealed design, the pressure is not transmitted by the air (that would require the "fixed" volume inside the ambient chamber to compress to a small fraction of it's initial volume) but rather the volume remains constant the the pressure is transmitted by the water pressure responding to the low pressure in the ambient chamber and pressing in on the diaphragm and on the transmitter via its contact with the diaphragm.
So the water has to press against the the diaphragm which has to be in contact with the transmitter inside the ambient chamber as it in turn presses against the main diaphragm (adding to the constant spring pressure) and in turn the diaphragmn presses against the pin pad, which keeps the seat off the orifice until the pressure is 145 psi above ambient pressure, regardless of whether ambient pressure is 14.7 psi or 200 plus psi.
----
What this all means is that to work properly the external diaphragm should be in contact with the transmitter (opr close to it) and tha tthe diaphragm will have to resist upwards of 100 psi pressure differentials on deeper dives. So it needs to be well supported and needs to be in good condition.
In that regard, I am in total agreement that the external diaphragm on a dry sealed reg must be replaced annually. It is not the same as the older environmental seal diaphragms used on an oil or alcohol filled ambient chamber where the liquid was largely incompressible (but expanded and contracted with temperature changes).
