Thu Jan 25, 2007 5:30 pm
It's called an R valve and us divers made them from 1955 to about 1958 or 1959. They called it an automatic reserve. When the tank pressure would get low, you did not need to flip a lever like with a J valve, all you had to do was just ascend and the reduced pressure on your lungs was enough satisfy your air needs. Needless to say, this wasn't ideal if your were in a situation where you couldn't immediately ascend. Such as a cave or a wreck.
When they first came out in 1955, they were a 2 step valve. On & off. In 1956, it became a 3 step valve like your valve. It was on, off, & fill. The top position was for filling your tank, middle position for diving, & bottom position was off.
I've used them in past, but I don't use them anymore because I'm a little bit nervous regarding the pin that keeps the knob on (the one that moves in the slots). I doubt anything would happen, BUT if that pin ever became fatigued and broke, the valve knob would shoot off and you would lose all your air like a blown burst disc. I'm not worried about the lost air, but more of the knob turning into a bullet. I'm not trying to scare you from using it, but just make sure the pin is in good shape.