5. DID YOU KNOW?
THE FINE ADJUSTMENT SCREW OF YOUR SECOND STAGE
Sometimes I observe that there are divers that turn the fine adjustment screw of its second stage; when I ask them why they do that, the answers are very diversed:
"... it's to give me more air!"
"to make it work better in depth"
"... if I tell you the truth, I'm testing what it's for!"
Certainly, the fine adjustment screw has a function, but it is not the one that many people think. I hope to be able to clear the doubts that there are about this simple device. The second stages, when they are balanced, have a mechanical system that consist on a spring exercing a force opposed to the pressure (that is inside the hose) and that is contained in the valve by a seal and that is actuated by a lever. This spring needs to be adjusted to counteracting the pressure coming from the hose, and to allows us to inspire with an effort similar to natural breathing (cracking pressure), and in addition it has to supplie us a volume of air contained in correct parameters.
Getting this is not too difficult when you have the right tools and instrumentation. This operation is done by an adjustment screw, which applies more or less tension to the spring, increasing or reducing the inspiratory effort or "cracking pressure". So far everything is quite clear, despite how boring my explanation may seem I have simplified it to the basics, now, what about the screw?
The certain thing is that when the qualified technician, after the annual revision, adjusts us the values of intermediate pressure of the first stage, and inspiratory effort in the second and OCTOPUS, the screw is in its most open position, so it means that it exerts the minimum pressure on the spring (which acts on the valve). The reason is very simple, by the normal use of the equipment, the valve acting on the seal is marked by the sharp edge of this and each time the mark will go making deeper (just a few microns) but enough so that the tension of the spring is not enough to contain the pressure of the hose, causing the leak that we usually describe as "THREAD OF BUBBLES". If the technician adjusts the opening pressure in any other position of the screw, tightened to the maximum, when the regulator begins to warn us with the bubble thread, the only possible path of the screw is to loosen it, so that the effect will be precisely the opposite than desired, the bubble thread will be a rather annoying jet.
It is at that moment, not before, that the user must squeeze a few (from 1/4 in 1/4 of a turn, for example) until the leak disappears, and that is usually the moment in which "we should" take to review our equipment. The reason, very simple: When tightening the screw we give more tension to the spring, increasing the opening cracking or, what comes to be the same, the regulator will become harder and may cause respiratory stress.
I would like to emphasize one thing about the adjustment of your regulators, when you send a regulator to an authorized technical service, you must request that they review the three basic elements, that is, the first, second principal and the octopus. You already know that the OCTOPUS is not for being used, but it would be terrible to need to give air to our partner and have to finish the dive, safety stop included, sharing air in anxiety. Also keep in mind that the cracking pressure has been adjusted according to the intermediate pressure of that first stage in particular, so I do not recommend that you change them to another first stage since, inevitably, the calibrations will vary with what, probably the operation of your second stage will not be the desired one.
I hope I have cleared any possible doubts about this element of our equipment and have been helpful.