Easier to breath = higher SAC rate ?

[LeadTurn_SD]

I'm inclined to disagree with folks here.

I use Apeks regs and I can adjust their resistance to cracking.

In the beginning I used to have this thing set to provide the lowest resistance which made it real easy to breath. I could suck on that thing till I felt like I was going to pass out. No shortage of air. However I always felt like I was getting too much. It felt like there was a micro second when I would stop inhaling and it continued to provide air.

My SAC was crappy. Still is to be honest with you.

One day I turned the knob so that it increased the cracking resistance. What I found was it took a few moments to get used to. I felt like I actually had to inhale. In the end though when I stopped inhaling, it stopped delivering.

My SAC improved by .1cuft/min. Blew my mind.

I can open it up all the way and decrease my SAC by .1cuft/min.

Maybe a reg tech can chime in here, but there is something to adjusting the resistance and SAC.

It is entirely possible, with an aggressively-tuned reg, to have a slight freeflow with the adjuster backed all the way out to the easiest position.

When I rebuild and tune my adjustable 2nd stages, I shoot for a setting just slightly more conservative than this. But others like to be able to get absolute maximum flow if they really need it, so they will tune for a very slight "leak" at the easiest setting.

What can happen with a 2nd stage tuned to this level is that it is taking a split second too long for the demand valve to close at the end of each inhalation (and the 2nd stage "burps" a little extra air, thus wasting it), or possibly even a tiny freeflow as you swim along. This will waste some air.

My guess is that this is what you might have been experiencing... or not

Best wishes.

 

[Atomic_Diver]

It is. Which is precisely why you cannot "walk too fast" simply by increasing the length of one stride. That's only distance.

:shocked2:

But if speed is distance over time, what happens when you increase the distance you travel by extending the distance traveled by an increase of how far you move with 1 step as an example, a person with long legs can travel 20' at 3mph and get there much quicker then someone much shorter then them... I think????

 

[Bubbletrubble]

Work of breathing is measured as joules per litre, or j/l. One litre is about the volume of one breath. A premium regulator will have a work of breathing of about .8 j/l and a cheapie will be maybe 1.8.

IMO, "ease of breathing" is not the same as "work of breathing." Ease of breathing incorporates more of a subjective take on how the reg performs. Does the reg deliver gas in a "natural" way? Does it start/stop when I think appropriate? Does it feel like it's force-feeding me gas at depth? Work of breathing is a quantitative measure derived from pressure-volume plots of reg performance. It's possible for a reg to have low WOB but not breathe in a "natural" way.

Harder to breathe regs tend to lead to elevated CO2 levels and elevated CO2 levels increase the urge to breathe. So a harder breathing reg has to cause an increase in CO2 levels that negatively impact your SAC rate. Alternatively the diver could compensate for the elevated CO2 levels and keep the SAC low by resisting the greater urge to breathe - in effect tolerating the higher CO2 levels. However this will, as an often unnoticed consequence, cause the diver to experience the increased narcosis that occurs with elevated CO2 levels.

Specifically, "it trains you to take slower more relaxed breaths" means "it trains you to tolerate higher CO2 levels."

I don't think that a "harder to breathe" reg necessarily implies CO2 retention. I think it's possible for a reg to be subjectively "harder to breathe" (after all, "harder" is a relative term) and yet still provide adequate ventilation. However, I do agree that if ventilation is inadequate (regardless of how it occurs), then CO2 levels in the blood will increase. In the short-term, this will likely increase respiration rate. It should be noted that some individuals might physiologically adapt and require higher CO2 levels to provide the same stimulus to breathe. As you pointed out, that's not a good situation since this can amplify the effects of nitrogen narcosis.

Could venturi effect be an additional factor affecting air consumption? If the venturi effect - as opposed to cracking pressure - force feeds air, then maybe that would increase SAC?

I had this same thought. As you know, the venturi effect makes it easier to keep gas flowing once flow has already been initiated. Combined with an aggressively set cracking pressure and "overbalancing" at depth, the venturi effect could theoretically contribute to gas flow beyond what the diver "needs" and negatively impact SAC.

In the beginning I used to have this thing set to provide the lowest resistance which made it real easy to breath. I could suck on that thing till I felt like I was going to pass out. No shortage of air. However I always felt like I was getting too much. It felt like there was a micro second when I would stop inhaling and it continued to provide air.

One day I turned the knob so that it increased the cracking resistance. What I found was it took a few moments to get used to. I felt like I actually had to inhale. In the end though when I stopped inhaling, it stopped delivering.

As Leadturn_SD pointed out, you are describing an aggressively tuned reg. If you know how the hydrostatic diaphragm works on the Apeks first stage, you'll understand how/why the "overbalancing" can feel like it's force-feeding air at depth. It's a feature that's designed to slightly increase the intermediate pressure at greater ambient pressure. Presumably this offsets the increased gas density at greater depths. De-tuning the second stage can mitigate this force-feeding phenomenon to a certain extent. It's probably not a good idea, though, to use an unbalanced second stage with the "overbalanced" Apeks first stage since this could cause freeflow at depth. AFAIK, Scubapro has a different definition of "overbalancing"...but that's another can of worms.

 

[marchand]

But if speed is distance over time, what happens when you increase the distance you travel by extending the distance traveled by an increase of how far you move with 1 step as an example, a person with long legs can travel 20' at 3mph and get there much quicker then someone much shorter then them... I think????

kind of like how a ton of bricks weighs more than a ton of feathers...

 

[trappist]

That is all interesting discussion
I'm not really trying to improve my SAC rate, s if I really want to get it down, I should stop carrying a huge catch back for my flounders or lobsters
I'm rather happy with my SAC rate even though I have the impression it is on the high side given my air integrated computer value ! But on the other hand I can do fairly long dives with my air so I won't complain ! Do I cheat if I say I dive a 120cf ???

Seems everyone is in favor of the fact my new reg might help to reduce the SAC rate... I will see this over time After a couple dives, I will compare the SAC rate of my A700 vs all my dives made with my G250. I'll try not to forget to report back with some data... the only thing is that it might take me a few months to get the data though

 

[miketsp]

It is entirely possible, with an aggressively-tuned reg, to have a slight freeflow with the adjuster backed all the way out to the easiest position.

When I rebuild and tune my adjustable 2nd stages, I shoot for a setting just slightly more conservative than this. But others like to be able to get absolute maximum flow if they really need it, so they will tune for a very slight "leak" at the easiest setting.

What can happen with a 2nd stage tuned to this level is that it is taking a split second too long for the demand valve to close at the end of each inhalation (and the 2nd stage "burps" a little extra air, thus wasting it), or possibly even a tiny freeflow as you swim along. This will waste some air.

My guess is that this is what you might have been experiencing... or not

Best wishes.

The reg doesn't necessarily have to be "aggressively-tuned" for this to happen.
It's the correct manufacturer setting on various regs.
Like the Aqualung Micra Adj.

From the technical manual:
3. Turn the second stage adjustment knob completely out
counter-clockwise. A slight leak of airflow should be present.
4. Slowly turn the adjustment knob clockwise, noting the measure
of turns required to stop the airflow. Airflow should stop
between 1/2 and 3/4 turn.

 

[dannobee]

I'm not so sure that slow, deep breaths INCREASE your SAC rate. As tacitly mentioned, CO2 is what causes our breathing response. Slow, deep breaths, both in and out, help flush out as much CO2 from our lungs as possible. This alone helped me decrease my SAC rate to 0.30-0.35 or so in warm water and 0.45 or so in cold water with a drysuit.

Through many different regs in various stages of tuning, it's been pretty constant at those levels.

Fix your breathing and relax during diving before thinking that the reg is gonna fix your SAC rate.

 

[Stu S.]

Ease of breathing incorporates more of a subjective take on how the reg performs. Does the reg deliver gas in a "natural" way? Does it start/stop when I think appropriate?

Sure. My daughter has an Oceanic regulator that gives the nicest swirl of air when you breathe a little, or a big flow when needed. A treat to use, so I like borrowing it. (I use Mares myself) I also have a 1977 Healthways that has always been more work. It has an exhaust valve the size of a nickel.

I know which one "feels" the best, but never noticed any difference in air consumption.

 

[LeadTurn_SD]

The reg doesn't necessarily have to be "aggressively-tuned" for this to happen.
It's the correct manufacturer setting on various regs.
Like the Aqualung Micra Adj.

From the technical manual:
3. Turn the second stage adjustment knob completely out
counter-clockwise. A slight leak of airflow should be present.
4. Slowly turn the adjustment knob clockwise, noting the measure
of turns required to stop the airflow. Airflow should stop
between 1/2 and 3/4 turn.

I knew I'd get corrected on that

You are right. "Aggressive" was not really the best term to use. Some manufacturers allow a slight leak at the easiest setting.... and that's just fine as long as you don't over do it with the amount of "leakage"

I'm a little more conservative, and turn the orifice in until the leak just barely stops at the easiest setting (for the Flathead VI / ZX regs I currently own).

Best wishes.

 

[Scared Silly]

Interesting question. When I switch from a Mares Abyss to an Atomic Z2 my SAC rate went up slightly. Not much, but what I attributed it to was it being easier to breath thus I took fuller breaths. As such, more gas and a higher SAC.