MK15/20/25/19 How about that?

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Bald Wookie

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That's a complicated question.

There is 1st stage choice and 2nd stage choice.
A lot of it is determined by regulator internals - materials, piston vs diaphram, sealed vs not, how well maintained it is, the list goes on.
Then there is how responsive each regulator is to user breath, how much air the reg flows, etc... this links with materials and how well its tuned.

The combination of 1st and 2nd stage, in tandem with tuning for the environment you're diving, makes huge differences. For instance in warmer waters even "lower end" regs generally breathe well, but in colder waters may be more prone to free flow.

For most people recreationally diving, ease of breathing and responsiveness is what you'll probably notice the most. If it feels like you're trying to suck a golf ball through a garden hose, you probably won't like that reg. Alternatively, I've breathed on regs that feel like they're gonna blow out the back of your head, so there is a balance there. Most people wont ever need to test out the maximum possible flow rate of regulators.

A full summary could fill a novel on what effects reg breathing differences.
 

rsingler

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...what makes one regulator set breath better than another? Is it not true that how it's how it's tuned by an expert like yourselves or a LDS who know what they are doing?
I think maybe that's a good subject for a new thread! While I ponder what to include, in what is indeed a quite complex topic, let's start with basic categories of reasons:
1) "Cracking effort"
2) Dynamic Flow
a) Venturi effects
b) Case design (which plays into a))
c) Poppet design (which plays into a))​
3) Air Density (which plays into 2))
4) Component Quality
and lastly 5) 1st stage contribution

1) Cracking Effort
Basically, how hard do you have to suck to open the valve? This is the single biggest factor, and fortunately, the easiest to fix.
My fiancee trained on my regs. But when she went to Hawaii for her OW dives, she air-shared on her Instructor's rental octo. It cracked so stiffly during the air-share ascent, she almost bolted for the surface in fear that she wasn't getting enough air. Fortunately, she kept it together, but surfaced with a new appreciation for well-tuned gear.

2) Dynamic Flow
a) Most modern designs are deliberately shaped to make use of the physical principle known as the Venturi effect. Basically (an oversimplification) when high pressure air goes thru a narrow opening (like your valve orifice) it tends to speed up, and the pressure on the downstream side drops. Inside a scuba regulator in mid-breath, the drop in pressure is almost enough to equal the suck you make to open the valve, and therefore keeps the valve open without you exerting any added effort. That's "easy to breathe"! If excessive, however, the reg will cross over into freeflow, as may happen when a reg hits the water without your mouth on it to offer any back pressure. Poor design or tuning can mean that there's no improvement in effort of breathing during the breathing cycle, in addition to what it takes to open the valve.
b) Case design - in the old days, a good breather was almost accidental. The Scubapro 156/Balanced Adjustable was hand brazed together with separate brass pieces before chroming. The case was ?accidentally? well shaped, but some regs delivered great flow, others didn't. But it didn't take long for manufacturers to recognize this contribution, and (for example) the Scubapro G250 consistently delivered great dynamic flow, with extremely low resistance mid-breath.
c) Poppet design - The Scubapro Pilot is the standard against which all other valve designs are measured. Extremely complex, it was also center-balanced. Without going into what that means, what that shape also has is an extremely short air path between the valve opening and the mouthpiece. Most all "standard" barrel design regs today instead have end-balancing, which necessitates that the air path leaves the valve, and travels down over the poppet and spring before making a turn out toward the mouthpiece. This affects dynamic flow, and must be accounted for when Venturi effects are added by design.

3) Air Density
When you dive deep the air literally gets thicker. At 132 feet, it is five times as dense as at the surface. That makes only a small difference in modern designs, but deeper than that, the sheer mass of air molecules has an increasing effect on Venturi pressure drops inside the case. This must be compensated for by design adjustments or other changes that can be made on the fly. It's complicated, but for the Recreational Diver is of little significance.

4) Component Quality
By this, I basically mean friction. Components that are poorly finished slide less well over other poorly finished components. This translates into greater effort at making things move, and without regular lubrication, can translate into "stiff" breathing.

5) First Stage Contribution
In the old days, many first stages were unbalanced. That meant that, if they were a piston design, the pressure they supplied to the second stage dropped as the tank emptied. At the same time, second stages were also unbalanced, which meant that the valve opened easiest when the pressure against it was the highest. With an empty tank, the result was predictable: decreased tank pressure equaled decreased "intermediate pressure" supplied to the second stage by the first, which then meant increasing effort (suck) to open the valve.
Nowadays, at least one of the two components is "balanced". Without going into detail, balancing means that (in a 1st stage) the pressure supplied stays more stable as the tank empties, or (in a 2nd stage) the negative pressure (suck) needed to open the valve is more stable over a wide range of supplied intermediate pressures.

What's the bottom line? Most modern designs of even the most inexpensive brands (due to competition in the marketplace) perform near identically IF they are tuned to the same cracking effort, WITHIN recreational depths. That means, if you feel a difference between your reg and your buddy's, it's most likely due to a difference in cracking effort, which can be solved with a quick retune.

The consequence of this improved design and manufacture, even with inexpensive gear, is that preventive maintenance on scuba equipment is often REALLY neglected, to the point that you don't see a difference until you're reaching that shoulder of the curve just before you "fall off the (performance) cliff".

Use @couv's Regulator Inspection and Checklist (Rev-8)
Read Pete Wolfinger's "Regulator Savvy" Scuba Tools (a bit of a yawn, except for equipment geeks).
Or at least, find a reg technician that you can trust. And that's a subject for an entirely different thread. Because "that guy" at the beach who can fix your freeflow, or improve your tuning, may not have any clue about the secondary (and potentially dangerous) effects of an isolated cracking effort change.
 

rsingler

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Have you communicated your concerns and recommendations to SP's tech. department? Why not if you haven't yet?
Just completed a contact form which detailed all the issues. We'll see if I get a reply. Thank you for urging me to do this.
 

BoltSnap

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Just completed a contact form which detailed all the issues. We'll see if I get a reply. Thank you for urging me to do this.

Good thing you did otherwise I would have been nagging you about it the whole time on SB :p
 

rsingler

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Just completed a contact form which detailed all the issues. We'll see if I get a reply. Thank you for urging me to do this.
Look at the wonderful reply I got from Scubapro!

Hello Robert,
Thank you for the feedback. I have made the necessary parties aware of your input.
Cordially,
Dan

::sarcasm on::
I'm sure the problem won't happen again!
::sarcasm off::
 

poseident

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I think maybe that's a good subject for a new thread! While I ponder what to include, in what is indeed a quite complex topic, let's start with basic categories of reasons:
1) "Cracking effort"
2) Dynamic Flow
a) Venturi effects
b) Case design (which plays into a))
c) Poppet design (which plays into a))​
3) Air Density (which plays into 2))
4) Component Quality
and lastly 5) 1st stage contribution

1) Cracking Effort
Basically, how hard do you have to suck to open the valve? This is the single biggest factor, and fortunately, the easiest to fix.
My fiancee trained on my regs. But when she went to Hawaii for her OW dives, she air-shared on her Instructor's rental octo. It cracked so stiffly during the air-share ascent, she almost bolted for the surface in fear that she wasn't getting enough air. Fortunately, she kept it together, but surfaced with a new appreciation for well-tuned gear.

2) Dynamic Flow
a) Most modern designs are deliberately shaped to make use of the physical principle known as the Venturi effect. Basically (an oversimplification) when high pressure air goes thru a narrow opening (like your valve orifice) it tends to speed up, and the pressure on the downstream side drops. Inside a scuba regulator in mid-breath, the drop in pressure is almost enough to equal the suck you make to open the valve, and therefore keeps the valve open without you exerting any added effort. That's "easy to breathe"! If excessive, however, the reg will cross over into freeflow, as may happen when a reg hits the water without your mouth on it to offer any back pressure. Poor design or tuning can mean that there's no improvement in effort of breathing during the breathing cycle, in addition to what it takes to open the valve.
b) Case design - in the old days, a good breather was almost accidental. The Scubapro 156/Balanced Adjustable was hand brazed together with separate brass pieces before chroming. The case was ?accidentally? well shaped, but some regs delivered great flow, others didn't. But it didn't take long for manufacturers to recognize this contribution, and (for example) the Scubapro G250 consistently delivered great dynamic flow, with extremely low resistance mid-breath.
c) Poppet design - The Scubapro Pilot is the standard against which all other valve designs are measured. Extremely complex, it was also center-balanced. Without going into what that means, what that shape also has is an extremely short air path between the valve opening and the mouthpiece. Most all "standard" barrel design regs today instead have end-balancing, which necessitates that the air path leaves the valve, and travels down over the poppet and spring before making a turn out toward the mouthpiece. This affects dynamic flow, and must be accounted for when Venturi effects are added by design.

3) Air Density
When you dive deep the air literally gets thicker. At 132 feet, it is five times as dense as at the surface. That makes only a small difference in modern designs, but deeper than that, the sheer mass of air molecules has an increasing effect on Venturi pressure drops inside the case. This must be compensated for by design adjustments or other changes that can be made on the fly. It's complicated, but for the Recreational Diver is of little significance.

4) Component Quality
By this, I basically mean friction. Components that are poorly finished slide less well over other poorly finished components. This translates into greater effort at making things move, and without regular lubrication, can translate into "stiff" breathing.

5) First Stage Contribution
In the old days, many first stages were unbalanced. That meant that, if they were a piston design, the pressure they supplied to the second stage dropped as the tank emptied. At the same time, second stages were also unbalanced, which meant that the valve opened easiest when the pressure against it was the highest. With an empty tank, the result was predictable: decreased tank pressure equaled decreased "intermediate pressure" supplied to the second stage by the first, which then meant increasing effort (suck) to open the valve.
Nowadays, at least one of the two components is "balanced". Without going into detail, balancing means that (in a 1st stage) the pressure supplied stays more stable as the tank empties, or (in a 2nd stage) the negative pressure (suck) needed to open the valve is more stable over a wide range of supplied intermediate pressures.

What's the bottom line? Most modern designs of even the most inexpensive brands (due to competition in the marketplace) perform near identically IF they are tuned to the same cracking effort, WITHIN recreational depths. That means, if you feel a difference between your reg and your buddy's, it's most likely due to a difference in cracking effort, which can be solved with a quick retune.

The consequence of this improved design and manufacture, even with inexpensive gear, is that preventive maintenance on scuba equipment is often REALLY neglected, to the point that you don't see a difference until you're reaching that shoulder of the curve just before you "fall off the (performance) cliff".

Use @couv's Regulator Inspection and Checklist (Rev-8)
Read Pete Wolfinger's "Regulator Savvy" Scuba Tools (a bit of a yawn, except for equipment geeks).
Or at least, find a reg technician that you can trust. And that's a subject for an entirely different thread. Because "that guy" at the beach who can fix your freeflow, or improve your tuning, may not have any clue about the secondary (and potentially dangerous) effects of an isolated cracking effort change.

I don’t disagree with any of these points, but feel it is worth mentioning that the diver’s own perception is also a big factor. There are regs I have loved that others have hated (sometimes this means “a good deal for you!). And I have known more than a few very experienced divers who swore they could never tell the difference between regs. Try several and when you find something that feels right, don’t be afraid to stick with it. But having access to a great tech can help you stay happy.
 

BoltSnap

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Look at the wonderful reply I got from Scubapro!

Hello Robert,
Thank you for the feedback. I have made the necessary parties aware of your input.
Cordially,
Dan

I'm sure the problem won't happen again.

Did you keep a copy of the entire message you sent them?
 
https://www.shearwater.com/products/perdix-ai/

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