- Reaction score
- Lake Jackson, Texas
- # of dives
- 1000 - 2499
No, you have it backwards. It's the pressure downstream of the 1st stage regulator that CLOSES the valve. If the tank doesn't have at least 150 psi in it, a spring fully opens the valve, and your LP hose and 2nd stage receive whatever pressure is left in the tank. The 2nd stage works similarly, where it will deliver air until the pressure in the hose gets down to (almost) the ambient pressure in your mouth.
Oops, I certainly did got it backwards. The spring is on the other side of the piston or diaphragm. Thanks for correcting my misconception on how the regulator works. So we can actually breathe down to the ambient pressure.
This video shows how the 1st stage regulator works: