Those were 30-45 minute bottles and the only way to tell you were close to running out of air was when the breathing became harder and harder. Then you simply pulled on the J valve that ran down the side of the tank and you had enough air to get to the surface. Can't remember how much PSI was left but at 50 ft I remember you had more than just a few minutes. The navy used them in their UDT program. First time I used one I couldn't find the ring to pull. Turns out I was fumbling around on the wrong side of the tank.
Do you like steel or aluminum tanks? Mine are old-like me-and steel.
