Adjustable or Non-Adjustable 2nd Stage?

[Akimbo]

So, (if I understand correctly) water depth really has no bearing on the adjustment? It has to do with water movement? So basically, as long as I'm not swimming into a strong current or playing with a DPV, there is no real need to spend the extra $$$ on an adjustable 2nd stage! (Or am I misunderstanding that?)

Yes, but as mentioned they don’t necessarily add to the cost when compared across manufacturers. A single manufacturer will usually use this feature to help differentiate and justify the cost of their higher-end models.

…The primary disadvantage to non-adjustable 2nd's is the inability to quickly "de-tune" them during a dive to prevent freeflows…

Agreed. There are a bunch of different names, but most regulators sold now have a knob or lever to minimize the annoying excessive freeflow when the regulator is out of your mouth — like an Octopus when you are entering the water. It usually modifies the flow dynamics in the housing, and reduces optimum inhalation resistance at high flow rates (like working hard at depth). Generally, this feature shows up on bottom to middle cost models and seat loading adjustment knob is added to as the price increases within a manufacturer’s line.

Atomic has a feature they call Automatic Flow Control which adjusts this action automatically based on depth where the highest flow performance is beneficial due to the increased gas density. This is in addition to the adjustment on the seat counterbalance spring.

 

[Akimbo]

… Statements like, "I don't intend to dive deeper than 80 feet" have a way of becoming untrue - quickly.

Very true, but there are no regulators sold anymore that don’t have very good to excellent performance at least to 130’/40 Meters due to requirements in the European Union. Chances are if you start diving deeper or evolve into technical diving you will need one or more low-end regulators for stage bottles.

There is a lot of logic for new and infrequent divers to purchase an inexpensive regulator, use them for two years with normal cleaning but without servicing, and then make the decision to service or sell & upgrade. We have all heard horror stories of regulators newly serviced at local dive shops failing. Badly assembled and tuned factory regulators are extremely rare.

 

[aacavalier]

Statements like, "I don't intend to dive deeper than 80 feet" have a way of becoming untrue - quickly.

Yeah....I've had a few things like that happen in my life! "Never say Never" right?

One of the LDS that sells Zeagle can get me a REALLY great price on all of my gear. I'm just wondering now which 2nd stage to go with! I like the idea of being able to tune the 2nd stage if need be, I'm just wondering if it's really worth it since there is a price difference in the different Zeagle 2nd stages that the LDS has! Even though I trust this particular LDS for dependability, they're all still "salespeople"!

 

[aacavalier]

So after reading a few more (different) threads on this issue, it seems that the biggest reason that people get the 2nd with the adjustment knob is to stop free-flow. However, I am seeing many new 2nds that have just the "dive/ pre-dive" lever with no adjustment knob. From what I am to understand, this lever is specifically for the free-flow problem? I need a 2nd that I can breathe out of, is dependable and doesn't have a bunch of useless bells and whistles.......though bells and whistles are sometimes a nice novelty!

 

[aquaregia]

The venturi will encourage a freeflow to continue freeflowing.

I tune my unbalanced adjustable very hot, then as the seat wears I can dial it in just a hair here or there to stop it bubbling. I can rebuild it after not aborting my dive

 

[LeadTurn_SD]

Yeah....I've had a few things like that happen in my life! "Never say Never" right?

One of the LDS that sells Zeagle can get me a REALLY great price on all of my gear. I'm just wondering now which 2nd stage to go with! I like the idea of being able to tune the 2nd stage if need be, I'm just wondering if it's really worth it since there is a price difference in the different Zeagle 2nd stages that the LDS has! Even though I trust this particular LDS for dependability, they're all still "salespeople"!

I'll take a stab at this, since a couple of the regulators I dive (and service) are Zeagle Flathead VI / ZX's.

The Zeagle 2nd stages can be purchased with and without the adjuster knob (but both have the "+" / "-" venturi lever). They are identical internally, and in fact if you buy the non-adjustable one, it can later be upgraded to the adjustable version in 5 minutes!

So their in-water performance is the same.... But you can in theory tune the adjustable version just slightly "hotter". This is because you can tune it for a VERY slight freeflow at the maximum "easiest" setting, then stop the freeflow by turning the adjuster in about 1/16 turn.

You cannot tune the non-adjustable version this "hot".

However, you would be very unlikely to actually DIVE with knob turned all the way out if the 2nd stage is tuned this "hot", because that slight freelow would result in a slight but constant air loss in between breaths. So in practice, you dive with the knob turned in just enough to stop the slight freeflow.... which would then result in the same performance between the adjustable and non-adjustable models.

So, the main advantage still comes down to being able to "de-tune" the 2nd stage when needed, not actually make it breath any "easier" than a non-adjutable 2nd.

And, having said all that.... I'd still recommend the adjustable Zeagle if you can afford it

Best wishes.

 

[redacted]

So after reading a few more (different) threads on this issue, it seems that the biggest reason that people get the 2nd with the adjustment knob is to stop free-flow. However, I am seeing many new 2nds that have just the "dive/ pre-dive" lever with no adjustment knob. From what I am to understand, this lever is specifically for the free-flow problem? I need a 2nd that I can breathe out of, is dependable and doesn't have a bunch of useless bells and whistles.......though bells and whistles are sometimes a nice novelty!

With most regulators, the dive/pre-dive switch is a venturi adjustment which does not prevent a freeflow but does limit the severity of the FF.

 

[LeadTurn_SD]

So after reading a few more (different) threads on this issue, it seems that the biggest reason that people get the 2nd with the adjustment knob is to stop free-flow. However, I am seeing many new 2nds that have just the "dive/ pre-dive" lever with no adjustment knob. From what I am to understand, this lever is specifically for the free-flow problem? I need a 2nd that I can breathe out of, is dependable and doesn't have a bunch of useless bells and whistles.......though bells and whistles are sometimes a nice novelty!

You've almost got it now

1.) The lever is mainly to limit the tendency for freeflow caused by venturi effect... the venturi effect is designed into 2nd stages to reduce breathing effort, but this effect will tend to hold the demand valve open when the regulator is out of your mouth, such as when you are climbing in and out of the water, or floating on the surface, and the reg is out of your mouth. The lever set in the pre-dive or "-" position does this by deflecting airflow in order to disrupt the venturi effect. It has no effect on opening or closing pressure of the valve itself; it simply helps reduce the tendency to freeflow if there is no "back pressure", such as the back pressure provided by having the reg in your mouth, turning it mouthpiece-down in the water, etc.

2.) The adjustment knob is a different animal. It actually effects the spring pressure acting on the valve, and thus effect the seating pressure in the 2nd stage demand valve, and thus effects how much breathing effort is required to open the valve. It can thus be used to increase spring pressure to stop slight leaks at the valve. This has the effect of reducing the "sensitivity" of the 2nd stage, and is especially useful in strong currents or waves/surf to make the reg less likely to freeflow while in your mouth (from water pressing on the diaphragm and purge). Tightening the adjustment knob will also make the 2nd less likely to freeflow when out of your mouth simply because it will take more pressure to open the 2nd stage demand valve... this is what is meant by "de-tuning" it: You are making it physically harder to breath.

These two adjustments will "overlap" a little in how they affect a regulator's tendency to freeflow when out of your mouth.

On my adjustable backup 2nds, or 2nds on stage or pony bottles I will have the venturi lever in the "-" position, and have the adjuster knob screwed in about 1/2 way to make the 2nd very resistant to accidental freeflow, but still "easy" to breathe (and a quick twist of the lever and knob returns it to full-easy setting).

Best wishes.

 

[superstar]

After numerous dives with adjustable regs and forgetting that they are adjustable and not taking advantage of their adjustability I just started using the non adjustable regs and life is much simpler now that I have one less thing to mess with on a dive.

 

[Centrals]

An adjustable 2nd stage will usually cost considerably more than its stable mate which isn't.
Take a look at Apeks XTX-200 and XTX-40. Any difference in performance? I don't think so.
I really do not believe a single screw can justify the added cost. OK there are other fine variations but the overall cost just do not add up.
People tend to believe performance, in this case a scuba 2nd stage, can be measured by the the price tag.