SAC worse with new reg

[Karlstumke]

I have about 150 dives on Scubapro MK25 / A700 carbon and get an average SAC of 9-10l/min for a chilled dive and HR around 80-85.

I now have 10 dives ln Apeks MTX-CR and my SAC is worse at betwwen 12-14l for dimilar HR. I have tried everything inclidung turning off the ventura abd dialling all the way with the cracking valve.

Do regs need a breaking in period. Do divers need to aclimitise to new air flows. It definately gave my dry mouth on first few dives but thats now hone.

Any ideas

 

[lexvil]

New Regs can usually need a tune up, adjustment, I’m not personally familiar with this APEKS but please explain the second paragraph, are you putting it in “pre dive” and which way are you turning the adjustment knob?

 

[Karlstumke]

New Regs can usually need a tune up, adjustment, I’m not personally familiar with this APEKS but please explain the second paragraph, are you putting it in “pre dive” and which way are you turning the adjustment knob?

Yes i keep it in predive and turn all the way in (clockwise). It breathes like a dream...

 

[lexvil]

Yes i keep it in predive and turn all the way in (clockwise). It breathes like a dream...

It should breathlike a nightmare, while everyone is different most people will use less air if they can breath easily.

 

[MidOH]

Ditto.

I open the adjuster nearly all the way once on the bottom.

Not sure how this is the regs fault. Might be in your head. Or different dive conditions.

I start my first dive on a snorkel. Seems to zen me. My air consumption drops 15-20% easy. Then I leave it on the boat for the rest of the week, once I'm in that relaxed zone. The point is, there's no scientific reason why that works for me.

 

[oya]

Give it a little time.

Different regs breath differently, they sound different, they feel different in your mouth. Everything about them is going to change your breathing pattern. You'll fall back into normal shortly.

One thing to check:
Take the reg out of your mouth during a dive at some point and see if there are little bubbles. If a second stage is tuned to just a little too close to a hair trigger (especially a modern, overbalanced reg and especially if they're brand new or recently serviced) as soon as they're exposed to higher ambient pressures they can start to leak just the littlest bit. That bleed of air into your mouth seems to drive a faster-than-usual breath response.

Edited to add: "Break in period" Yes, there is one. As a brand new soft, silicone seat starts to take a memory of the hard, brass crown indenting into it over and over with each breath it can be prone to these sorts of tiny bleeds of air.

 

[LI-er]

It was my understanding that the "inspiratory resistance adjustment knob" should be turned clockwise to set it for "predive" and this makes breathing more difficult and would therefore require a diver to work harder with each breath thus increasing SAC rate, while conversely, turning it counter clockwise for diving will decrease diver effort to take breaths and decrease SAC rate (while increasing chances of a free flow).

That much being said, I've been diving an older Beuchat regulator and upon reading this thread I realize that I haven't changed the setting from whatever it happens to be in as long as I remember.

 

[stepfen]

Welcome to subsurface @Karlstumke !

Sorry but a consumption of 9-10lt/min is very low for the average diver. Are you sure about it?
Furthermore, assuming that indeed you have 9-10lt/min, an increase to 12-14lt/min is quite big (all other things being similar). Think about it: You are telling us that on average about 30% (about 3lt per breath) of the gas you breath is wasted for EVERY breath during the whole of your dive! This, or you breath ~30% faster for the whole dive. That's huge difference.

Things like adjustment knobs, or not ideal tuning, break-in periods etc can't have such dramatic effect, unless there is a (substantial) leak in your new reg (that would be very obvious).

I think there is something else going on here.

How do you measure your SAC? Are the conditions indeed similar for the dives you are comparing?

 

[Karlstumke]

Welcome to subsurface @Karlstumke !

Sorry but a consumption of 9-10lt/min is very low for the average diver. Are you sure about it?
Furthermore, assuming that indeed you have 9-10lt/min, an increase to 12-14lt/min is quite big (all other things being similar). Think about it: You are telling us that on average about 30% (about 3lt per breath) of the gas you breath is wasted for EVERY breath during the whole of your dive! This, or you breath ~30% faster for the whole dive. That's huge difference.

Things like adjustment knobs, or not ideal tuning, break-in periods etc can't have such dramatic effect, unless there is a (substantial) leak in your new reg (that would be very obvious).

I think there is something else going on here.

How do you measure your SAC? Are the conditions indeed similar for the dives you are comparing?

I use Garmin mk2i with transmitter that has setting for cylinder size etc. That's the readings it calculates. To adjust for different dive conditions i use average Heart Rate as this would reflect stress or effort. However looking at my logbooks there doesn't even seem to be a correlation with that. Even if these calculations are not 100% accurate it still compares like for like.

One dive HR is 78 and SAC is 9.5 with Scubapro and week later HR is 78 and SAC 11.3 with the Apeks.

I think I will put a few more dives on it and see..

 

[stepfen]

I use Garmin mk2i with transmitter that has setting for cylinder size etc.

Hmmm... This could explain your low consumption. Are you sure you are using the correct tank size? For example in several parts of the world 11.1lt tanks are commonly refereed to as 12lt. In your case this particular misconception would make your measured SAC worst than your real one - not better as in your case, but still are you sure you are using the correct tank size? What matters is not what people call them but the number that is written on their neck.

Sorry but without knowing much about you (experience, amount of dives, training, comfort underwater, equipment, diving conditions etc etc) it is difficult (but for sure not impossible) to have such low gas consumption. So I'm looking for sources of error.

Now about the increase in your SAC with your new reg. There are a lot of factors that can impact SAC. Heart rate is one of them - but translating one to the other is not as straight forward, I think.

In my case, for relaxed wetsuit dives I usually have a SAC of about ~12lt/min (after about 450 dives over 8 years). With drysuit I have much less experience (about 50 dives over 3 winters that I use drysuit) hence my comfort level is much lower and my SAC rices easily to about 15lt/min. But this is a quite different setup (drysuit, more lead, heavier fins, cold water, etc).

Another thing that might be affecting your SAC is that maybe you worry too much about it (or other things). Maybe you don't trust yet your new reg setup? Maybe you are overthinking about it? Maybe something else? Worrying about things (including gas consumption) during the dive definetly increases SAC.

For a so noticable increase in your SAC I would look for this kind of factors. A small mistunning, or breathing effort difference shouldn't cause so drastic SAC increase.

That's my 2c as always. I let other, more experienced divers further comment.

All the best....