breathing effort difference between 2 first stages...help

[Luis H]

Herman,

I think that is my point--you only need a balanced second stage if you have an unbalanced first stage. And even if you do, you will still get more fluxuation of cracking pressure than you would with a balanced first stage and an unbalanced second stage. The latter combination can be tuned within a few psig of by the IP, and it will not vary with varying tank pressure. This technology has been in use since the 1960s. It is still my contention that if a regulator has both a balanced first stage and a balanced second stage, the diver is being sold something (s)he doesn't need.

SeaRat

I have converted most of my Scubapro 109 to Balanced adjustable for two reasons, the performance and the long term longevity of the initial tune.

The light spring on the balanced second stages seem to minimize the indent on the soft seat and therefore so far my Scubapro Balanced adjustable have not needed any service for years and the performance doesn’t seem to change. They get very little use, but in storage I never use any kind of seat saver. I am afraid of hurting the rubber diaphragm cover.

The cracking effort is not the performance improvement on a balanced second stage. It is possible to adjust a down stream to have a very low cracking effort. The 109 can be adjusted to the exact same cracking effort with its original down stream demand valve or with the balanced valve.

The different comes in at the required suction during the rest of the breathing cycle. The balanced second stage is affected substantially less by the IP dip that normally occurs during inhalation. Obviously the less the IP dip (from better first stages) the less significant is the improvement of balanced second stage, but there is always some IP dip from all first stages.

I agree that the performance difference may not be significant to most divers and that a good venturi will provide a similar advantage, but the light spring is IMO a big advantage in reducing long term maintenance.

My Balanced Adjustable just breath great and they have not been serviced in years.

BTW, a balanced second stage is not 100% balanced. They are intentionally designed with some bias so they still behave as a relief valve in the case of a first stage leak. Otherwise you will need an over pressure relief valve.

 

[halocline]

In theory you can adjust a 109 to have the exact same cracking effort as a b/a, but my meager experience has been that my b/a poppets can usually be tuned to a slightly lower cracking effort. I don't really know why. I don't have a gauge to measure the cracking effort, I'm just judging by submerging the reg.

I agree that the effort needed to sustain the breath in a balanced 2nd is lower, although Awap claims he cannot consistently tell the difference in performance between his 109s and b/a. I suspect that the minimum cracking effort is less than the reg will tolerate in use due to case fault geometry, so in practice they both need to be tuned to the limits of that.

I assume another reason that the balanced reg requires less effort to sustain inhalation is that part of the force holding the poppet against the orifice is air pressure in the balance chamber at IP. When IP dips during inhalation, the pressure in the balance chamber drops as well, lessening the force keeping the reg closed. So not only is the balanced 2nd less susceptible to IP drops, but the drop actually lowers the opposing force to inhalation.

I also keep most of mine as balanced primarily because they take less of a seat imprint.

 

[Luis H]

I assume another reason that the balanced reg requires less effort to sustain inhalation is that part of the force holding the poppet against the orifice is air pressure in the balance chamber at IP. When IP dips during inhalation, the pressure in the balance chamber drops as well, lessening the force keeping the reg closed. So not only is the balanced 2nd less susceptible to IP drops, but the drop actually lowers the opposing force to inhalation.

Yes, I didn't think that I needed to explain that (and my post was already long enough), but I am glad you did.

In theory you can adjust a 109 to have the exact same cracking effort as a b/a, but my meager experience has been that my b/a poppets can usually be tuned to a slightly lower cracking effort. I don't really know why. I don't have a gauge to measure the cracking effort, I'm just judging by submerging the reg.

Since converting to Balanced Adjustable, I haven't played much with original 109. Therefore, I can't really say that I have done any detail side by side comparison of before and after. I am just going by memory of the results from the 109s that I have serviced and the one 109 that I haven't converted yet.

My over all impression is that cracking efforts are similar (maybe not exactly the same), but the sustaining suction is consistently lower with the BA. This comes from taking readings with a Magnehelic (we have had one on every dive shop I worked in and I now own a few).

 

[John C. Ratliff]

See, this is how an ol' guy learns new things. Thanks to both Luis and Mattboy for very interesting posts.

SeaRat

 

[Couv]

Chris, I will try to bring it by next week and let you have a look at it. I can leave it for you if I get a chance to make it by earlier.

Now you know I'm going to wind up getting the sealed HOG first anyway but this is just for couriosity sake...

Jeremy

Jeremy & Chris,

How about an update? I am interested to know the diagnosis and resolution.

Thanks,

Couv

 

[cerich]

he hasn't dropped by