Making sure you have breathing gas at depth
A common practice for years in the diving industry was to open your tank valve all the way and then turn it back ¼ turn. We are going to look at the reasons that this practice was started, and then why it should be discontinued.
Why does everyone want to turn the valves back ¼ turn?
When diving was in its infancy, not so long ago, the valves were made with materials that would stick under pressure, so if you opened the valve all the way, and then went on a dive, by the time you got back to the surface, you would not be able to turn your tank off. Therefore, in the beginning, everyone was taught to open the valve all the way, and then turn it back ¼ turn to avoid this situation.
Why is this dangerous?
In preparing to dive, if you close your valve and open it ¼ turn, it will breathe the same on the surface as it will if you open it all the way and close it ¼ turn. The problem occurs when you get to depth. Under pressure, you can easily over-breathe a regulator that is only open ¼ turn, making it feel like you have suddenly run out of air. This can lead to panic and a rapid ascent. To avoid this, common practice today is to open the valve all the way, and leave it open. This way, if you accidentally close the valve, you will notice it during your pre-dive safety check when you breathe off of your regulator to make sure you have air.