A demand valve is driven by you inhaling, when you stop inhaling the flow stops.
I'm pretty sure a valve forcing air into your lungs would not be a good idea to be honest, seems good way to actually blow your lungs out.
but the pressure directly behind the demand valve is being matched to the pressure where you are. this doesn't force air into your lungs because the pressure on the outside of your chest matches the pressure in the air in front of your mouth.
this is why you use your air faster on a deeper dive, and why you get oxygen toxicity if you go too deep without special air mixtures
Yeah you're totally right. I had misunderstood how the action of the demand valve worked. Commented further down this thread on my mistake. Owe that to you also.
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u/theZombieKat Aug 18 '22
that air in the tank is pressurized, and the regulator matches the output pressure to local pressure.
at 3 feet it would be like breathing with somebody sitting on your chest, hard but possible.