Beginner 7 minutes
The Aqua-Lung: the invention that cut the umbilical cord
1943, a demand valve, and the birth of diving as you know it
Before 1943, diving usually meant being tied to the surface by a hose and depending on someone continuing to pump. After 1943, it came to mean carrying your air with you and swimming free. Rarely has a single piece of engineering changed an entire activity so much.
In this article you'll see what technical problem the Aqua-Lung solved, what precursors it had (quite a few more than usually get mentioned) why the demand valve is the key idea, and how it went from a wartime prototype to a worldwide industry in two decades.
The gear you wear today is a refined version of that design. Understanding what that valve solved explains why you breathe as easily as you do, and why the equipment is so simple to use.
The problem that had to be solved
Carrying compressed air was already technically possible in the early twentieth century: there were vessels capable of holding gas under pressure and systems to reduce it. The problem wasn't storage, it was delivery.
A continuous flow of air, the first solution tried, works but wastes gas massively: the air keeps coming out whether you breathe or not, which makes for very short endurance. It also requires manually adjusting the flow rate every time depth changes.
What was needed was a system that delivered air only when the diver inhaled, and did so at exactly the surrounding water pressure at every moment, without the diver having to touch anything.
That's the definition of a demand valve, and it's the heart of modern dive equipment, as described in the article on how a regulator works: a mechanism that detects the pressure drop caused by inhalation and opens the gas path right at that moment.
The concept wasn't new. Already in the second half of the nineteenth century, in France, Rouquayrol and Denayrouze had developed an apparatus with a working demand valve, although in practice it was mostly used with a surface air supply, because the pressure vessels of the time couldn't withstand high pressures.
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