Balanced Diaphragm Reg Performance - Is This Typical?

[Locus]

As I continue to rack up more dives I am getting increasingly familiar with my equipment, and I started noticing something about my regulator:

As I ascend during the second half of my dive, my second stage breathes more easily as soon as I reach 10m. It has gotten to the point where I can tell that I have reached this depth without looking at my computer.

When I am at my max depth (~30m) I do not notice any problem getting all the air I need (though I have not yet encountered a stressful situation at this depth, so I have not yet demanded the maximum that the reg can provide under pressure), so it's not as though I'm choking at depth or anything.

My regulator is a balanced diaphragm model made by Mares (MR 42 1st stage, Carbon 42 2nd stage).
Is this noticeable difference in depth/performance typical of this type of reg or does it sound like it needs adjustment?

 

[LeadTurn_SD]

What your are describing is not typical in my experience. I primarily dive with balanced diaphragm firsts, including Mares MR-22, Mares MR-12, and Zeagle Flathead VI first stages, and a variety of 2nd stages attached to them. I do not notice a difference in breathing resistance related to depth. All of my regulators, included balanced and unbalanced 2nd stages attached to the 1st stages I mentioned seem to breath the same at various depths... in fact, I sometimes feel that they breath better as I descend, but that could just be my imagination.

I do notice differences in breathing resistance related to orientation of the 2nd Stage (looking up, looking down, head-up, feet-up, laying on my back, etc.) but this is related to the physics of how regulators work.

I don't have an easy answer for what you are describing, maybe some of the "usual suspects" can chime in.

Best wishes.

 

[underH2Oman]

A balanced regulator should perform the same regardless of the depth change. If it is noticeably easier when you get to 10m during ascent, it means it was noticeably harder below 10m and that would concern me.
I think you should have it checked.

 

[LeadTurn_SD]

A quick additional note... all regulators are depth compensating. Balanced first stages simply retain a stable or near-stable Intermediate Pressure as tank pressure changes.

Best wishes.

 

[lemke]

Cracking pressure is adjusted too low, or your poppet spring is too weak for some reason. I'm not familiar with Mares regs, so this is a very general suggestion.

 

[LeadTurn_SD]

Thinking about this a bit more... I wonder if your 1st stage IP is creeping up at the end of the dive, as tank pressure drops??

Your 2nd stage is I an unbalanced classic downstream I believe, so if the 1st stage IP crept up, breathing resistance would drop...

Just guessing at this point. I bet Herman or one of the other "diaphragm" guys will have a good answer.

Best wishes.

 

[rjk75]

Locus,

You ought to post this question on the Mares forum: Mares... Just add Water!

However, I'm curious: what was your starting pressure on the surface, and did you happen to look at your tank pressure again when you ascended to your 10m depth?

And just a suggestion, you ought to get yourself an IP gauge (they're not expensive) if you don't have one already. I have an MR42T with Abyss 2nd and I've noticied my IP drops from 145 psi with a full tank (2600 psi, I use LP tanks) to about 135 psi when tank pressure falls down to about 1600 psi. The latter IP is measured out of the water of course, in a pool environment.

I now record my starting and ending IP readings in my log book for reference.

 

[Fishpie]

That's a bit unusual.....a diaphragm reg usually does the opposite.
Intermediate pressure increases as tank pressure drops.....hence leadturn's previous post.

 

[LeadTurn_SD]

That's a bit unusual.....a diaphragm reg usually does the opposite.
Intermediate pressure increases as tank pressure drops.....hence leadturn's previous post.

That's what I was thinking... but thinking about it a little more, with his first stage I would not expect much IP change at all, until the tank pressure gets quite low. My Mares 1st stages seem to hold the exact same IP throughout a "normal" range of tank pressures, but honestly I've never tested them much below about 1,000 psi... I usually test at 3,000 psi with a full tank when I service them, and then at whatever "lower" pressure I have in other tanks I have lying around.

Puzzling.

To the OP: I would get the 1st stage tested. If your shop has a flow bench, they should be able to test it through a range of pressures and see if it is acting strangely.

Best wishes.

 

[herman]

Considering that is a balanced diaphragm first I doubt the Ip is varing much if any and even if it is, the second stage is also balanced so it will compensate for small changes in IP. What he may be experiencing (a SWAG I admit) is an overly (depending on your preferences) aggressive venturi in the second stage. I don't have any experience with that reg but I do play around a good bit with the venturi on the DH regs I experiment with and they will change with depth if set up fairly aggressively. I like them on the aggressive side so I tend to set mine up on the edge. As the depth increases so does the density of the inhaled air, that increase in density tends to increase the effectiveness of a venturi. Most venturies are not set up that agressive so you don't notice the effect but he may have a "good" one.