Conservative Tech?

[rsingler]

Are Atomics worth the cash?

 

[Ojai Diver]

Thanks for your replies, and thanks rsingler for the link.

Okay I will id the regs in question:

First stage: SP Mark 11
Second: SP A700

What the tech told me (I am NOT trying to argue, just repeating what was said to me) is that the Mark II is overbalanced, meaning it has a lower IP at high tank pressure, which increases as the tank pressure goes down. The end result, (again, HE SAID) is that the reg becomes easier to breath as the tank is breathed down.

 

[rsingler]

True at 150' (5-6 atm) with thick air. Undetectable at most rec depths.

And I'm presuming you meant the Mark 11,
Not the Mark 2 (II).

 

[Ojai Diver]

Yes, the Mark 11. And, to be clear, I am not trying to trash the tech, who seems very good, refused my money and did these adjustments gratis. Just trying to learn more about the process.

 

[herman]

Thanks for your replies, and thanks rsingler for the link.

Okay I will id the regs in question:

First stage: SP Mark 11
Second: SP A700

What the tech told me (I am NOT trying to argue, just repeating what was said to me) is that the Mark II is overbalanced, meaning it has a lower IP at high tank pressure, which increases as the tank pressure goes down. The end result, (again, HE SAID) is that the reg becomes easier to breath as the tank is breathed down.

If he said exactly that, find a new tech, he has no clue what he is talking about. Not only does he not know what balancing does (first stage), he has it mixed up with overbalancing which is actually a misnomer, it is actually over depth compensating.....which has noting to do with balancing. First stage balancing is solely to keep IP constant as tank pressure varies which in turn keeps cracking pressure of the second stage constant over the range of tank pressure, that's it. Balancing has nothing at all to do with depth.
All regs are depth compensated which means the IP varies to compensate for varying ambient pressure (as you descend or ascend). With a "non-overbalanced" reg, the IP increases or decreases as you descend or ascend in a one for one ratio. For example, at the surface say your IP is 130 and ambient pressure is 0 (yea I know its 14.7 but for ease call it 0 since that is where we start). When you go descend to 33ft, the pressure around you (aka ambient) increases to 15 psi (again rounding) so your reg will increase the IP by 15 psi to 145psi but at the same time the pressure around your second stage has also increased by the same 15 psi so the difference between ambient and IP is the same -130 psi and the second stage breathes the same. On the other hand, the misnamed "overbalancing" is actually over depth compensating. It too varies the IP as you change depth but since it is "over compensated" it does so in a nonlinear fashion. Instead of increasing by 15 psi at 33ft it will increase by some value more, typically around 10% more. So at 33 ft your IP will increase by around 16.5 psi instead of the 15 of the non-overbalanced reg.
So, what does this all mean overbalancing stuff mean, well in short as you decend the IP of your first stage will continue to increase more than is needed to compensate for the increase in ambient pressure. If you are using an unbalanced SECOND stage, the cracking pressure will go down but at some point start it will start to freeflow, which is the main reason I don't care for overbalance first stages. If you are using a balanced SECOND stage, basically nothing happens (at rec depths) since the whole purpose of balancing a second stage is to compensate for varying IP to keep cracking pressure constant. As the IP gets "overcompensated" the balanced second stage continues to preform as normal since it's design to compensate for varying IPs.

 

[rsingler]

It's all good. Just ask the tech for 0.9" on the A700, or maybe even 0.8" (since you can screw in the adjustment knob). Then try it out. With the smaller A700 case, it should work out fine. Just be prepared to go back to the shop if it starts to freeflow a little after a few months.

And @herman , without stirring the pot too much, don't you think that over-depth-compensating might be of some value in providing a balanced second with a higher driving pressure, given the air density concerns at 5 atm? Not that I'm sure the Mk11 actually does that.

 

[herman]

Some for sure but we are talking machine level testing. No diver will tell the difference, remember the second stage is a demand valve so you only get what volume of air you demand regardless of the density of the gas (within reason). The volume you demand is the same at any depth and until you get way past normal rec depths does the density really start to be an issue. Besides the increase in IP at 100 ft is roughly 45 psi of a "normal" reg as opposed to 50ish for an "overbalanced" reg, roughly 5 psi not really enough to make a difference in practical terms. It's enough to make a well tuned unbalanced second stage start to gently freeflow but not much else.

 

[fmerkel]

With shop equipment the tech can make those adjustments in about 5 minutes. Yes, he was doing you a favor, but it's not a big deal for him.

 

[Couv]

what was said to me) is that the Mark II is overbalanced

Are you sure you don't have a MK17? I think the 17 is overbalanced (like Herman I don't like the term as it does not describe the effect) while the MK 11 is not overbalanced. I was given to understand that the so called overbalancing is a side effect of having a sealed diaphragm. I'm not a SP diaphragm guy, so those in the know please feel free to correct me.

....which increases as the tank pressure goes down.

The above describes Intermediate Pressure Inversion-nothing to do with overbalancing.

Just ask the tech for 0.9" on the A700, or maybe even 0.8" (since you can screw in the adjustment knob). Then try it out.

Bingo! That is the beauty of having an adjustment knob.

 

[buddhasummer]

Ultimately, I agree.



Interesting. So for the G260 above (for example) are you saying it can be adjusted to less cracking effort than its specs? If so, why would a tech be reluctant to do so? Are they obliged to deliver in spec? Or is there some performance trade off?

Yes, when I dove G260s I set them at .9" and they were fine. Out of the box from factory one was cracking at 1.6".