adjustable airflow reg and air consumption

I was wondering if tightening or loosening the adjustable airflow knob found on certain regs has any impact on your air consumption rate. Lately I've been thinking that it doesn't impact your consumption rate too much since you you need a certain amount of air to fill your lungs whether your reg breathes easy or hard. But today I was diving with my reg loosened up quite a bit more than last year and my air consumption rate was a lot worse than usual. now this could be due to the fact that I haven't been in the water all winter and I've gotten rusty, but I'm not sure. What do you guys think?

Normally the harder you have to work to breathe the more air you will use.

Easier breathing= more relaxed= less air used.

(I normally set mine to the easiest possible breathing setting without having a constant flow).

And it is normal for your air consumption to go up when you haven't been in the water for a while- so now you have an excuse to get out and dive more often.

I agree.

Generally speaking, the knim position doesn't have much of an effect on air consumption. However, I once set my Zeagle so "loose" that it was dumping air into my mouth even when I wasn't inhaling. Really bad SAC rate on that dive!


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your reg shouldn't force air into your mouth neither should you have to force air into your mouth by breathing from a regulator. I have an adjustable 2nd stage and have it set just so.

If you're working to breathe underwater then you're expending energy and therefore oxygen. If your reg is almost free-flowing into your mouth then the air will just pop out of your nose and waste your air supply.

More than likely its due to being out of the water for a while. Relax, breath slowly... and did I say relax!?

Safe diving,

C.

I agree with TC, you must relax, breath efortless, as if you were breathing through your mouth in the surface, or even a little easier than that. Hard breath will make you spend energy to suck your reg and usually cause CO2 build up as well, because you tend to breath short and quick (like a tired dog), this does not vent your lungs well and should cause you to acumulate too much CO2, so besides cosuming more air you get also a nice headache. Almost freeflowing isn't good as well, as Crowley mentioned.


In extreme cases CO2 build up can be very dangerous, making you loose consiousness, what in the water usually means drowning, or slowing your thoughs, which is specially dangerous when you have big task load, like in multiple gases deco dives, you could make confusion when switching gases, or even "forget" some deco stops, there are documented accidents caused by CO2 build up causing the diver to jump deco stops.

Adjust your reg to be very confortable, easy breathing, but make sure the air comes only "when asked".

Ivobj - where can I read up on this CO2 buildup? Long times in cold water can also contribute to headaches?

If anything you were out of practice or had some excessive drag to deal with. Reducing the breathing resistance would not increase the gas usage unless you were actually to the point the reg was in a slight freeflow and even then that would not have made much difference. Increased cracking pressure and work of breathing would increase the workload and therefore increase gas use but the increase would be barely noticable, the increased use would likely only a few breaths.

The only reason you should have it closed (turned in/tightened) is for boat diving or rough shore entry to avoid freeflow. Once the reg is in your mouth underwater it should be completely opened.

Diving Low:

Ivobj - where can I read up on this CO2 buildup? Long times in cold water can also contribute to headaches?

Click to expand...

Hi, there are some interesting articles and accident reports that mention CO2 build up, among them the famous accident that killed David Shaw, which cause was CO2 build up. Some links below:

Dave Shaw died from carbon dioxide black-out - Divernet

Vary interesting article...

http://www.red-sea-shadow.com/downloads/HeadachesAndScubaDiving.pdf

While explaining about headaches caused by CO2 build up they also mention the issue of heavy breathing as a cause.

QUOTE
The best treatment for this type of headache is to take slow, deep breaths to reduce the build up. Also use
high performance regulators that have good flow characteristics.
UNQUOTE

About the issue of headaches due to cold water, it is probably less frequent than CO2 build up, build can be a reason as well, I found that in a book:

QUOTE
Cold water may be the main guilty of your headache. Head freezes more quickly than other parts of the body, because many vessels are just under the skin and they are not protected with fat layer as in other parts of our body.
UNQUOTE

Also, as cold is a vessel constrictor, it tends to make harder the blood flow, so this also can cause headaches, as your head and hands usually are the less protected areas of your body in cold water specially, assuming you are diving dry.

Hope this helps.