Inhalation adjustment knobs

[scuba393]

I'm considering purchasing the Aqualung Legend. Both seem the same except for the LX model having the inhalation adjustment knob. Is diver adjustable inhalation important on a regulator, or is it simply a feature that costs more and adds complexity to the regulator, but that divers really don't use? If I purchase the standard Legend (not LX), will I be missing out on significant breathing adjustability, or will I probably not notice nor care?

 

[Bubbletrubble]

Some people have regs with inhalation adjustment knobs and really like them. This allows one to modify the cracking pressure of the second stage during the dive. Such knobs really aren't necessary, though. A properly tuned/serviced reg will have a reasonable cracking pressure and should not be prone to free-flow.

My Apeks regs have inhalation adjustment knobs. I use the knobs on every dive. Typically I'll de-tune my backup reg a little. I don't dive in significant currents often, but when I do, it's nice to be able to de-tune both the primary and backup second stages on the fly.
My Aqualung Legend regs lack the knobs. They breathe great.
Personally, I don't feel strongly about the knobs one way or another. Whatever you decide on getting, make sure you buy an i.p. gauge to help monitor reg performance over time. Having an i.p. gauge and learning how to tune/maintain your reg will probably make more difference in the long run than having an inhalation adjustment knob.

Hope this info helps...

 

[LeadTurn_SD]

I own regulators both with and without adjustable 2nd stages.

The advantages of adjustable 2nd stages are:

1. The ability to detune the regulator to prevent freeflows in a current or on the surface.
2. The ability to tune the 2nd stage a tiny bit more "aggressively" (so that it will actually freeflow slightly at the easiest breathing setting), so that if the need arises, you can get "maximum" performance from the 2nd stage...
3. The ability to store the regulator with the adjustment knob turned all the way out, which takes a bit of pressure off the soft seat and may prolong it's life a bit between services.

You'll note that I did not list "better performance"; that is because my experience with my own regulators is that a correctly tuned non-adjustable 2nd will breath essentially the same as an adjustable 2nd set to its easiest breathing position... unless the adjustable reg is tuned fairly "aggressively"; then I notice an ever-so-slight advantage with the adjustable reg.

The biggest factor will be in how carefully the tech "tunes" your regs at service time.

Having said all of that.... if the price difference is not too great, I'd probably get the adjustable reg.

Best wishes.

Edit: Bubbletrubble and I were posting at the same time I think we are saying about the same thing

 

[Jimmer]

I am a proponent of adjustable regs. Here is why.

When I started diving doubles, I was using a set of Oceanic Alpha 8's on CDX5 first stages. Non adjustable, workhorse regs. I did what all the experts told me to do and I had my primary setup very light, and my backup setup slightly stiffer so it wouldn't free flow. Well one dive I had my buddy suddenly had a massive freeflow and panic. I gave him my primary, switched to my backup, and while I had never noticed it before in training, all of a sudden the de-tuned second stage was very noticeable at 125' and stressed out.

After that I sold them off, and bought some fully adjustable Zeagle Flathead VI's. I had them setup to breathe the same, and just dial the backup down. Same thing happened with a different buddy, I gave him my primary, switched to the backup, dialed it open to full bore, and was very pleased at that moment that I had an adjustable reg.

Also, I have been on COLD DEEP dives and felt my reg starting to very slightly hiss a bit of air between breaths. I just turned the dial about a half a turn tighter and the hiss went away. If that had happened on the non adjustable Oceanics, I'm pretty sure it may have accelerated into a full on free flow in another minute or two.

I dont mind non adjustable in warm shallow water, but no way I would use them in cold deep dives.

Jim

 

[Bubbletrubble]

When I started diving doubles, I was using a set of Oceanic Alpha 8's on CDX5 first stages. Non adjustable, workhorse regs. I did what all the experts told me to do and I had my primary setup very light, and my backup setup slightly stiffer so it wouldn't free flow. Well one dive I had my buddy suddenly had a massive freeflow and panic. I gave him my primary, switched to my backup, and while I had never noticed it before in training, all of a sudden the de-tuned second stage was very noticeable at 125' and stressed out.

@Jimmer: Your story is not really proof that the Alpha 8 should not be dived in cold water due to its lack of an inhalation adjustment knob. It's pretty clear that the cracking pressure on your backup Alpha 8 was set incorrectly (cracking pressure too high). For some reason, I was expecting you to say that the aggressively tuned primary free-flowed as soon as you took it out of your mouth and offered it to your buddy. That was not the case, though. I suspect that if you had just tuned your backup to match the cracking pressure of your primary, then you wouldn't have had any problems with initiating flow at depth. Perhaps people with more reg service experience might be able to comment on this.

As far as I know, an inhalation adjustment knob on the second stage is not a requirement for cold water diving. One should set the i.p. on the first stage towards the low-end of the normal range, ensure that the first stage is environmentally sealed, and install the standard heat-sink gizmos on the second stage (or use a metal second stage). But, then again, I don't have much experience diving in truly cold water.

I do value your input, Jim. Perhaps I'm missing something here. At some point, I would be interested in doing some cold water diving, so I'm curious.

 

[LeadTurn_SD]

Regarding tuning of non-adjustable 2nd stages used as "octo's":

As a "crutch" to sloppy handling on the surface, many non-adjustable 2nd stages are severely detuned by techs and at the factory. My feeling is that significantly detuning an octo is a mistake, and causes the the exact problem that Jimmer described.

As DA Aquamaster pointed out in another recent thread, a properly tuned 2nd stage should not freeflow once submerged and flooded.... Thus there is no good reason to de-tune a non-adjustable octo to double (or worse!) the cracking effort of your primary.... Yet I've seen this level of de-tuning in non-adjustable octos.

The Mares repair manual (Mares 2nd's are non-adjustable, unbalanced, classic downstreams) specifies only a slight difference in tuning between primary and octo.... just a few tenths of an inch cracking effort.... if your primary is set at 1.2", your secondary is at 1.5" or so.... but no more than 1.9"... not at 2.5", 3.0", etc.

If you tune an octo so that it will never freeflow at the surface.... you have a poor-breathing octo when you need it most. A better solution is to handle the properly-tuned octo at the surface carefully, and deal with the occasional momentary freeflow when you aren't careful.

Best wishes.

 

[vinegarbiscuit]

@Jimmer: Your story is not really proof that the Alpha 8 should not be dived in cold water due to its lack of an inhalation adjustment knob. It's pretty clear that the cracking pressure on your backup Alpha 8 was set incorrectly (cracking pressure too high). For some reason, I was expecting you to say that the aggressively tuned primary free-flowed as soon as you took it out of your mouth and offered it to your buddy. That was not the case, though. I suspect that if you had just tuned your backup to match the cracking pressure of your primary, then you wouldn't have had any problems with initiating flow at depth. Perhaps people with more reg service experience might be able to comment on this.

As far as I know, an inhalation adjustment knob on the second stage is not a requirement for cold water diving. One should set the i.p. on the first stage towards the low-end of the normal range, ensure that the first stage is environmentally sealed, and install the standard heat-sink gizmos on the second stage (or use a metal second stage). But, then again, I don't have much experience diving in truly cold water.

I do value your input, Jim. Perhaps I'm missing something here. At some point, I would be interested in doing some cold water diving, so I'm curious.

If I'm not mistaken, the Oceanic Alpha is an unbalanced second stage. Even when paired with a balanced first stage, the unbalanced second stage would still adversely affect work of breathing. (I had a similarly-configured Sherwood, and I was pretty miserable at depths over 50 feet.) I'm so glad you got the Zeagle Flathead - from what I've heard and read, it sounds like a fab reg.

Sorry to go slightly off-topic. To the OP: you won't have to worry about any of that, as the AL Legend is a superb reg, with or without the adjustment knob. I too prefer having that feature - lots of my dives have current, and it's nice to dial back the reg when needed, or feel like I can turn it up and give myself a little 'oomph' at depth.

 

[Bubbletrubble]

As a "crutch" to sloppy handling on the surface, many non-adjustable 2nd stages are severely detuned by techs and at the factory. My feeling is that significantly detuning an octo is a mistake, and causes the the exact problem that Jimmer described.

@LeadTurn_SD: This was my impression, too. I don't want to pick on Jimmer, but shouldn't the hard-breathing backup reg have been detected while switching to the backup in the course of normal "during-the-dive" checks? It makes sense to me to switch back and forth from primary to backup a few times during every dive since I'd rather find out about cracking pressure or free-flow issues during a check rather than when a buddy is truly OOA. Am I the only one who does this? I don't know...maybe this is just poor cold water diving technique.

If I'm not mistaken, the Oceanic Alpha is an unbalanced second stage. Even when paired with a balanced first stage, the unbalanced second stage would still adversely affect work of breathing. (I had a similarly-configured Sherwood, and I was pretty miserable at depths over 50 feet.) I'm so glad you got the Zeagle Flathead - from what I've heard and read, it sounds like a fab reg.

@vinegarbiscuit: If Jimmer had identical second stages and the poor performance could be attributed to the second stage design, wouldn't his primary also be breathing hard at depth? This is why I think it was an issue of de-tuning the backup too much. FYI, I'm assuming that the balanced first stages were adjusted properly and in good working order.

I really do want to thank Jimmer for sharing his experience. I think this discussion highlights the importance of properly tuning the reg. I suspect that many people have a negative experience with a crappily tuned reg...and allow this to affect their subsequent purchasing decisions: "Never again will I use a reg made by XYZ manufacturer." In the end, however, a diver should have confidence in his/her gear. If that means paying a little more for a feature that makes one feel safer, then there's nothing wrong with that, budget permitting, of course.

 

[LeadTurn_SD]

If I'm not mistaken, the Oceanic Alpha is an unbalanced second stage. Even when paired with a balanced first stage, the unbalanced second stage would still adversely affect work of breathing....

Hi vinegarbiscuit,

In theory, the balanced 2nd stage can breath easier than an identical model and identically-tuned unbalanced 2nd because a lighter spring can be used in the balanced 2nd.... so less effort is required to get the demand lever moving as you inhale even though the seating pressure required to seal the demand valve would be the same... at least this is how I understand the theory.

Reality: It all depends on the design of the unbalanced 2nd. A well designed unbalanced 2nd will breath VERY well at all depths.

I currently dive balanced, adjustable 2nds (same reg as Jimmer, Zeagle Flathead VI/ZX) and unbalanced, non-adjustable 2nds (Mares Abyss).

I've tested both regs on the same dive / depth (had the Zeagle on a stage, the Mares as my primary), and can detect only the slightest difference in breathing performance. The depth when I compared them was just over 100', so it was a fairly deep recreational dive.

At the easiest breathing setting, my balanced, adjustable Zeagle ZX 2nd has just the very slightest edge in ease of breathing over the unblanced, non-adjustable Mares Abyss, simply because I've tuned the Zeagle fairly aggressively, and the Abyss is tuned to the low end of "factory spec". I'm very satified with how the Abyss breathes, so I have not tried to "push the envelope" on how aggressively I can tune it.

Best wishes.

 

[LeadTurn_SD]

@LeadTurn_SD: This was my impression, too. I don't want to pick on Jimmer, but shouldn't the hard-breathing backup reg have been detected while switching to the backup in the course of normal "during-the-dive" checks? It makes sense to me to switch back and forth from primary to backup a few times during every dive since I'd rather find out about cracking pressure or free-flow issues during a check rather than when a buddy is truly OOA. Am I the only one who does this? I don't know...maybe this is just poor cold water diving technique.

....

Hi Bubbletrubble,

I think most folks "accept" hard-breathing octo's as standard... I did, until I started following various threads here over the past few years and began servicing my own regs (8 sets and counting, lol). I do test breathe my secondary each dive, and used to accept that it was a bit harder to breath than my primary, and figured that was "normal".

This was not brought up in this thread: But even underwater, when any well-tuned reg is just "popped" out of your mouth, there will be a tendancy for it to freeflow if you do not handle it carefully...

I'm a warm water wuss, so I don't know much about good cold water technique.... but my guess is that test breathing the regs underwater is "ok", as long as you are careful to avoid the "sloppy handling" freeflows; so this is where I'd definitely prefer an adjustable 2nd that is "cranked down" a bit so there is no chance it can get bumped and freeflow.... one of the "chilly" divers needs to answer this one

Best wishes.