The tank pressure behind the volcano orifice is what actually creates the pressure thrust (force) to balance the forces so that the output IP is not affected by the tank pressure, creating a balanced piston system.
What everyone calls a floating orifice (volcano orifice) is technically a secondary piston in this system. The orifice is exposed to tank pressure on the back side, intermediate pressure (IP) on the other side, and the force of the primary piston sealing against the volcano orifice. By definition, they this system has two pistons. And the summation of the pneumatic and spring forces makes a balanced system with a consistent pressure output.
The Belleville washer spring is just part of the system springs that plays a part on balancing the summation of forces.
The new Poseidon balanced diaphragm regulator works in the same principle with a “floating” orifice that (part of a moving piston) that reacts to the tank pressure. The pneumatic and spring forces create a balanced system that closes the valve at the same output pressure (IP) and it is not affected by the input tank pressure.
I don’t know how well balanced is the Poseidon diaphragm first stage regulator, but I do know that the Sherwood output IP is very precise at any tank pressure.
