I was taught to turn the tank valve on all the way, then a quarter turn back. I didn’t ask why at the time and yet many years later I found myself telling my students the same thing. Never once did anyone ask me why and I proceeded as if that was the way it was meant to be. Only when I started technical diving, did my instructor tell me to open the tank valves fully and that was the way they were to stay throughout the dive. Not wanting to sound stupid, I didn’t ask at the time and figured that in tec, it was just different. DAN (Divers Alert Network) recently recommend that all divers, be it recreational or technical open their tank valves fully.

As it transpires, the reason divers turned the valve a quarter, or indeed half turn back stemmed from decades ago when the brass valves did not have a buffer between the spindle and the valve housing. If you didn’t turn the knob back a half turn then the valve would shrink during the dive due to cooling, and you wouldn’t be able to turn it off afterward. This is not a problem today, but old habits die hard, and many divers still turn the valve back half a turn. Regardless of which – would you rather have a tank valve stuck open or closed mid-dive?!

A different reason for keeping the valves open all the way is that it can cause confusion; I have seen many divers do the buddy check and turn their buddy’s tank off, then a quarter turn on. This is not a big problem initially, but when you’re on the dive and consume an amount of air, it goes beyond how much air the valve can let out of the tank in its partially open position. As you can imagine, this leads to an assumed out-of-gas situation on the dive and if you’re like most divers who are too far away from their buddy, you are left with no alternative but to CESA or make a buoyant ascent to the surface. If you’re close to your buddy, then you should switch to their alternative regulator, and then you can check whether you are actually out of gas or whether your tank isn’t turned on correctly. In either situation, it is imperative that you keep calm and react in a controlled manner.

Equally, I see a lot of divers forgetting to turn their tank on at all whilst kitting up, however the tank is still pressurised and so the SPG reads 200bar. All good, they think and merrily trot off to get in to the water. An extremely important check to do is to take a few breaths from the regulator whilst watching the gauge. The needle should remain at 200bar, if it starts going down in time to your breathing, then it’s a pretty safe bet that your tank isn’t turned on properly. This check also avoids the over-helpful-buddy situation, when they could turn the tank off thinking they are turning it on.

So from now on, turn your tank valves all the way on, until it doesn’t go any further (you do not need to use Hulk-like strength with these valves) and make sure you double check before you get in to the water that you can breathe from your reg and the needle doesn’t move down.