halocline
Contributor
Certainly one of the most stable 2nd stage in different positions is the scubapro D series. You'd be buying a used reg, so you can disregard this if that bothers you. You could find a D400 with a MK10/15/20 on ebay and have it rebuilt.
The thing that makes regs breathe differently in different positions is case fault geometry, which is a result of the difference in depth between the diaphragm and the exhaust valve. If you can think about it, the diaphragm is what keeps air pressure in the 2nd stage at ambient, because if it drops below ambient, the diaphragm collapses a little, which pushes the lever and opens the reg, filling it with air. The exhaust valve prevents air pressure inside the reg from exceeding ambient, because if pressure exceeds ambient the exhaust valve simple opens and lets the air escape. When the exhaust valve is higher in the water column than the diaphragm center, there is less pressure on the inside of the 2nd stage because the exhaust valve is the limiting factor on pressure in the reg, and that's slightly shallower. When the reg is upside down, (like when you're on your back looking up) the exhaust valve is deeper than the diaphragm, which means internal pressure in the 2nd stage case is higher and it takes more effort to collapse the diaphragm.
The D series regs deal with this by placing the exhaust valve coaxial with the diaphragm so there is never significant difference between their depths. The design also angles the diaphragm and places it sort of under the diver's chin, so it very rarely is found at a disadvantage (shallower) to the diver's mouth. This solves the case geometry fault issue, and the balancing mechanism uses a spool to provide a relatively high degree of air balancing, which allows the reg to have a very light spring.
But, yeah, if you want you could just go buy an expensive atomic barrel poppet reg. I'm also a little surprised about the legend "dying" unless it got smashed up somehow. Other than physical damage outside of normal use, regs don't usually "die" unless rebuild parts become unavailable.
The thing that makes regs breathe differently in different positions is case fault geometry, which is a result of the difference in depth between the diaphragm and the exhaust valve. If you can think about it, the diaphragm is what keeps air pressure in the 2nd stage at ambient, because if it drops below ambient, the diaphragm collapses a little, which pushes the lever and opens the reg, filling it with air. The exhaust valve prevents air pressure inside the reg from exceeding ambient, because if pressure exceeds ambient the exhaust valve simple opens and lets the air escape. When the exhaust valve is higher in the water column than the diaphragm center, there is less pressure on the inside of the 2nd stage because the exhaust valve is the limiting factor on pressure in the reg, and that's slightly shallower. When the reg is upside down, (like when you're on your back looking up) the exhaust valve is deeper than the diaphragm, which means internal pressure in the 2nd stage case is higher and it takes more effort to collapse the diaphragm.
The D series regs deal with this by placing the exhaust valve coaxial with the diaphragm so there is never significant difference between their depths. The design also angles the diaphragm and places it sort of under the diver's chin, so it very rarely is found at a disadvantage (shallower) to the diver's mouth. This solves the case geometry fault issue, and the balancing mechanism uses a spool to provide a relatively high degree of air balancing, which allows the reg to have a very light spring.
But, yeah, if you want you could just go buy an expensive atomic barrel poppet reg. I'm also a little surprised about the legend "dying" unless it got smashed up somehow. Other than physical damage outside of normal use, regs don't usually "die" unless rebuild parts become unavailable.
