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May 2019    Download the Entire Issue (PDF) Available to the Public Vol. 45, No. 5   RSS Feed for Undercurrent Issues
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Thereís an Easier Way to Dump Air from Your BC

from the May, 2019 issue of Undercurrent   Subscribe Now

At the risk of trying to teach a grandmother to suck eggs, here's something to think about: During an ascent, do you lift the corrugated hose of your BC alongside your head to release air through the oral inflation valve? If so, why?

You may be familiar with old film footage of Jacques Cousteau's divers, using triple tanks and wearing little else than their Speedos, a mask and fins. That was in the 1970s, when recreational diving really took off, and one of the first things sport divers demanded was neoprene wetsuits to keep the chills at bay. Before that, divers wore sufficient weight to stay down, but because bodies are incompressible, their buoyancy stayed constant. Alas, the introduction of neoprene insulation with its tiny integral bubbles introduced a variable into the equation: buoyancy changed as the diver went deeper, and those bubbles got smaller.

This was when -- and why -- the buoyancy compensating device, or BCD (later abbreviated to BC), was introduced. It first came in the form of a horse collar. The diver removed the regulator from his mouth and blew into a mouthpiece at the end of a corrugated hose to add air to compensate for loss of buoyancy as he went deeper. That expanding air had to be released the same way as the diver ascended, so he raised the oral inflation valve on its corrugated hose to the highest point, to allow air to escape. Diving instructors taught their students that technique, and when those students went on to be instructors, they taught their students to do the same, and so on. It became enshrined in scuba diving practice.

Most modern recreational BCs come equipped with dump valves placed at the shoulder and the lower back. They are designed to enable air to be jettisoned without letting too much water back in. Some divers worry these valves will dump all the air from a BC in one go, letting them then plunge to the depths. It patently isn't so.

So what's wrong with using the oral inflation valve to dump air instead, just like you were taught? Nowadays, divers tend to make a lot more dives per day, thanks to diving computers. Constantly releasing expanding air through the oral inflation valve also lets water enter. During the course of a week, a lot can re-enter, and your BC will have a lot less air than it should, just when you might need the maximum lift during a long wait to be picked up at the surface.

Of course, you can always fully inflate the BC at the surface and evacuate that excess water through a bottom dump valve, but how many recreational divers know that?

Better yet, get in the habit of using the valves the BC designer went to the trouble to add for you. Just because your diving instructor taught you to use the corrugated hose and oral inflation valve doesn't mean it's the best route to take, any more than you still need to start your car by means of the crank handle.

The oral inflation valve is simply for that -- inflating your BC at the surface when you don't have access to air from the tank.

-- John Bantin

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