This is what one of my Discover scuba diving participants scream at me the other day in the pool. Parents poolside looked horrified and being the helpful DM that I am finned over and promptly turned the reg down preventing further gas leakage. Faces relaxed and then relieved, as if I’d just thrown myself onto a live grenade and averted a major crisis. In my head i thought to my self…
I tried to explain that this is an occurrence that happens sometimes in diving at that it’s in no way a cause for concern in a confined pool session but i can see how it takes someone by surprise and can be a little frightening. However I’m sure everyone has experienced the inconvenience which is the free flow. Annoying, air depleting and dangerous in cases. Hopefully all that remember their PADI open water training will think back to practising breathing of a free flowing regulator.
What is free flow? How can we prevent it? And what to do if it happens to you! Fear not friend, all will be revealed.
Free flow is a diving term used to describe an uncontrolled venting of gas from a regulator. This isn’t necessarily due to a malfunction or a poorly adjusted regulator and most instances happen from simply entering the water.
Free flow has two distinct types as well. The first being trickling of bubbles escaping at a slow pace. The other one which you’ve must likely experienced is the gushing free flow which at the surface acts as a nice jacuzzi. But your not here to pamper yourself, your here to dive!
Why does it happen then?
Normally it’s related to the venturi effect that is caused by air rapidly leaving the regulator – which essentially lowers the pressure in the second stage case and keeps the diaphragm depressed. This can happen by jumping in from a boat or poolside. Embarrassing…
The most common cause of free flow is due to cold conditions and the icing of regulator components. This happens due to the physical properties of gases. When a SCUBA cylinder is filled large numbers of particles are forced into a small space causing an increase of heat. Therefore, conversely when gas leaves the cylinder it cools. You can sometimes see this effect when emptying a cylinder when a small amount of frost will form on the valve if it’s emptied rapidly enough.
Frost is bad m’kay. It freezes key components of your regulator causing free flow. So to summarise, when the surrounding water is cold (below 10 degrees centigrade) and something triggers a free flow such as entering the water via giant stride or taking your reg out while it’s pointing upwards, the cooling can cause valves to freeze open! The only way to get rid of this type of free flow is to close the tank and bring it up to re-warm. See how it become potentially dangerous now? Fair enough jumping in but what if it happened at 20m at the end of a dive?
So what can we do to stop this?
- Firstly we can make sure that all our equipment is properly serviced, ship shape and Bristol fashion.
- If you dive mainly in a cold water environment, consider buying a sealed first stage and a cold water rated second stage. Apeks also make special hoses to help eliminate free flows.
- Make sure when you enter the water than regulators are facing down and that knobs, buttons etc.. are switched to the minus setting, which increases the effort required to breathe.
- Promptly stop free flows with appropriate methods e.g. by jamming your thumb in the mouthpiece or if need be, shut off the cylinder.
I accept this is a fairly random post and not all the angles are covered e.g. the venturi effect (which a cheeky post will be appearing about asap). However I hope you’ve enjoyed at least the pictures or lolling whale sharks and a monkey jacuzzi.
As ever feel free to call me out on any mistake and helpful comments, tips and hints are always appreciated!
Stay narked 😉