Pneumatically Balanced 2nd Really True???

[Couv]

Hello all,

As stated earlier, one of the advantages of a balanced poppet is that it allows for a larger orifice. I have not measured the difference (and I'm at work right now) but is there a difference in the orifice size of the 109 and BA (G250 etc) I am converting my 109 second stages to BA. Is a change in the orifice also called for?

Thank you,

couv

 

[DA Aquamaster]

It's the same orifice in both the R109 and the R156. Either way, you'd want to stay with the old orifice as the old ones were brass while nearly every orifice Sp has produced (including replacement parts) since about 1994-95 has been made of plastic and is not quite as sharp as the older chrome plated brass orifices or as durable.

 

[DA Aquamaster]

A balanced second stage will also perform better if the first stage IP swings any noticeable amount during the inhalation cycle.

Granted most respectable 1st stages would probably only drop about 5 to 10 psi during a normal breath cycle (the MK-25 may be less, I don't know), but even a small amount of pressure drop will create a small force imbalance with a conventional down stream second stage.

During heavier breathing this transient IP drop can be much more noticeable with some first stages.

A pneumatically balanced 2nd stage will tend to compensate for that.

The irony here is that many companies tend to pair unbalanced second stages with unbalanced first stages to create an entry level reg, and then pair an unbalanced second stage with a balanced first stage to create an intermediate level reg, but don't pair a balanced second stage to an unbalanced first stage - a combination that in many ways would be beneficial addition to the intermediate reg category as it would produce good inhalation performance with a less expensive and often more compact unbalanced first stage. For recreational divers not needing an uber performance first stage that option would provide good inhalation effort at cost.

 

[Luis H]

The irony here is that many companies tend to pair unbalanced second stages with unbalanced first stages to create an entry level reg, and then pair an unbalanced second stage with a balanced first stage to create an intermediate level reg, but don't pair a balanced second stage to an unbalanced first stage - a combination that in many ways would be beneficial addition to the intermediate reg category as it would produce good inhalation performance with a less expensive and often more compact unbalanced first stage. For recreational divers not needing an uber performance first stage that option would provide good inhalation effort at cost.

I have been wondering about that.

My gut feeling is that the reason they don’t offer that combination has very little to do with cost and more with how regulators marketing has evolved. It seems the marketing wants to pair up the latest new second stage to their top of the line first stage.

Also there seems to be way too much emphasis on the first stage. I have noticed that some of the first questions that most beginners ask are related to the 1st stage: diaphragm vs. piston, balanced vs. unbalanced, etc. Maybe the name “first stage” gives the impression that it is the more important part of the regulator.

In reality, I am sure you agree, that the performance of the second stage is far more critical to over all performance than the first stage. The first stage all it has to do is provide a relatively constant IP. How constant is a function of how tolerant is the second stage.

A Scubapro MK-2 with G250V would probably be a great, reliable, fairly cold water regulator, but who in marketing want to put one of your latest great performing second stages with your least expensive first stage. Well, it makes sense to me, but what do I know…that is probably part of the reason of why I am not in marketing.

 

[DA Aquamaster]

I asked this at a service clinic once and was advised that SP's marketing strategy was to field combinations that created entry level, intermediate and advanced regulator packages with the goal of selling perhaps as many as three regulators to a given customer as they advance in their career.

I got the impression that SP regarded a balanced first stage as being an essential element of an "intermediate" regulator. But it does ignore the larger issue that a good balanced second stage, by the nature of its design can compliment and overcome the limitations of an unbalanced first stage and that the brute performance of an upper end first stage is really only needed in extreme conditions that most recreational divers will never see.

Personally, I like the early warning effect you get from an unbalanced first stage (even with a balanced second stage) with increased inhalation effort as the tank pressure drops below about 300 psi. I also like the extreme reliability and O2 freindly traits of an unbalanced piston first stage. Consequently, I use an unbalanced piston first stage with a balanced second stage on all of my deco bottles. It offers more than enough performance at decompression stop depths of 130 feet or less as well as bullet proof reliability while at the same time providing low inhalation effort - an important consideration when deco is half or more of the total dive time.

A suitably cleaned and prepped SP Mk 2 G250V would be ideal in this situation, and for recreatioanl diving at 130 feet or less would offer much smoother breathing and lower inhalation efforts than a Mk 2 R190 or even a Mk 11 or 17 paired with an unbalanced second stage.

The consequences of that would be that the average recreational diver would be very satisfied with the reg and would be very unlikely to upgrade to a more expensive balanced first and second stage combination.

Another factor may be that most of the dealer cost and markup in the regulator packages as they move up the entry level/intermediate/advanced scale is in the second stage and customers would perhaps not be as impressed with the differences in cost versus performance between on first stage and another, so I suspect the packages are assembled to compel customers to upgrade both stages to get a particular feature or adjustment.

But on the positive side, SP does allow dealers to sell any first stage with any second stage and the cost of buying them separately is only a few percent higher than in a package - and in he end it is far less than the cost of upgrading to a balanced first stage when you don't really need it.

 

[Luis H]

The irony here is that many companies tend to pair unbalanced second stages with unbalanced first stages to create an entry level reg, and then pair an unbalanced second stage with a balanced first stage to create an intermediate level reg, but don't pair a balanced second stage to an unbalanced first stage - a combination that in many ways would be beneficial addition to the intermediate reg category as it would produce good inhalation performance with a less expensive and often more compact unbalanced first stage. For recreational divers not needing an uber performance first stage that option would provide good inhalation effort at cost.

I also find it very ironic (as I mentioned in another post) that some regulator manufacturers are pushing the overbalanced first stage and then pairing it up with their top of the line balanced second stage. By design the balanced second stage would not only not take much advantage of the first stage, it for the most part defeats the "overbalanced" feature in the first stage.

The logic behind some of the marketing is always amazing and some times amusing.

 

[halocline]

I've put my G250 on my MK2 and it breathed really well, I could not tell a difference between the MK 2 and the MK15 on the one dive I took that combination on.