Atomic servicing: which is more important 1st or 2nd stage

[fdog]

Hello James,

From reading some of your other post I'm sure you know this already and you probably just make a fingerfelder; but, just for clarification, usually when tolerances are given, they are either given in a range such as 125 to 145psi OR they are given as 135 +/- 10 psi.

Now that isn't to say you will never see a spec given like 120 +10 -0 psi, but I think you see the point.

Cheers,

Couv

Well, that's what I get for being quick and brief! Thanks Couv.

The exact quote from the Atomic technical manual is:

Intermediate pressures should be between 125-145 psi with a spread no more than 7 psi.

All the best, James

 

[halocline]

I get my Atomic 1st stages rebuilt 2-3 times as often as their 2nd stages.
But, then again. I often run excessively high tank pressures (aka "cave fills")
and this tends to beat up the seats in the first stages,
while having no adverse effects on the second stages.

It shouldn't really have an effect on the HP seat, at least I don't think so. There is a force required to make the piston seal against the seat, that's IP minus whatever downstream and spring force is trying to open the valve. Assuming atomic 1st stages are designed similarly to SP MK25s (I know they are) then the HP section is designed to not have any appreciable downstream force on the piston edge. This leaves IP minus spring force, and if your IP is the same, the seating force must be the same. IOW, if when you overfill your tanks you notice that the IP is substantially higher, that's an indication that the seating force required to seal the increased pressure differential at the piston/seat is higher, which could result in more rapid seat wear. But if your IP is the same as when you have lower tank pressures, then the force on the seat must be the same.

I've heard before that overfills (or just HP tanks in general) are hard on 1st stages, it never really made sense to me, so I decided to really think about it, and that's what I came up with. Luis would be a good guy to ask about this.

Now, if you're finding that you have IP creep in a few months of use, something's causing it but I don't think it's high tank pressure.

What does make sense to me is that very high tank pressure will put extra stress on the HP piston o-ring, which directly seals supply pressure from ambient. You could have your tech try a 90 duro polyurethane o-ring in that spot, if atomic doesn't use one already. I've had great results with those o-rings in my MK10s and MK5s, which lack the bushings that your atomic has. The bushings are supposed to keep that o-ring from extruding, so it might not have any effect.

 

[halocline]

What does atomic mean by "spread"? Is it IP rise from 500 to 3000 PSI or is it creep?

I can definitely tell you that if I spent that much money on a reg and it creeped 7 PSI by design I would not be happy.

 

[fdog]

I'm not the designer (all I've done is take the class) but 7 psi is the reject point. Not the designed creep. I don't think anyone designs a regulator to creep.

Anyway, to me, IP creep is something similar to what afflicted the Apeks regulators about 6 years ago: an IP that starts out normal, and progressively gets higher and higher as the dive continues, or, as the regulator gets more and more use.

...If you want to be shocked, try measuring IP (with a high resolution gauge) from 3000 psi to 500 psi with a diaphragm regulator. It's pretty easy to exceed a 10 psi spread.

In any case. the final test is in the breathing. I would challenge anyone to tell a 10 psi difference in IP from a regulator with a high-quality second stage. I know I can't.


All the best, James

 

[halocline]

Okay, so that's not creep, it's IP swing as the supply pressure changes. They're saying that a 7 PSI drop in IP from 3000 to 500 is acceptable. Creep is when you cycle the reg and it does not lock up at a stable IP immediately, but the needle "creeps" up several PSI. It's indicative of a poor seal at the HP seat.

 

[tfsails]

I would suspect that the 7psi "spread" is the difference between low and high input pressure. All unbalanced first stages (except Sherwoods) have an IP shift as input pressure increases. Balanced first stages, whether diaphragm or pistion, are supposed to maintain a relatively steady IP regardless of input pressure. That's where (I think) the "spread" comes in. I've seen balanced 1st stages have as much as a 10-15 psi variance between high and low input pressures. I've also seen them where there was no variance at all.

Some manufacturers mention the spread in their technical literature, others don't. I guess it's just a matter of what kind of regulator you have.

I've seen some regs (unbalanced diaphragm) where the book allows a 15psi creep after lockup. Others only allow 2-4 psi. As mentioned above, "creep" is not "spread" in my book.

 

[Mtbr]

Having been through the regulator class from Atomic, I would say the 1st stage. The 2nd stage is tough and has the best internal parts I've seen.

With that said, why wouldn't you get them both serviced at the same time?


All the best, James

My budget is tight. I was thinking the B2's 2nd stage is made of Ti, not much should go wrong. Maybe just get by with the 1st service.

 

[Couv]

Mtbr,

If you have taken good care of your equipment, your regulator may not need servicing at all. See this sticky thread to help you decide for yourself.

http://www.scubaboard.com/forums/regulators/260452-regulator-checklist-inspection.html

c

 

[cbmech2]

Agree with other posters in their stance that servicing one of the two isn't such a good idea and doesn't make sense. However, if I absolutely had to choose and assuming that you dive with an octo. The first stage would be your single pont of failure and would likely take all of your redundancy out (primary second and octo) if it were to have a catastrophic failure. Atomic first stages are very similar to the SP MK10 with differences in materials used in some cases. They are very simple, rugged and reliable. At least if your first stage is functional and your primary second failed, you would have your octo as a backup. I really do recommend though that you service both, but even if you choose to only do one, they must be bench checked as a whole and tuned together to ensure proper performance.

 

[drbill]

I don't use Atomics (yet) but with my SP Mk10/G250s I do try to service both at the same time (when I can afford it). I've had to have the first stage rebuilt separately when one developed very strange vertical cracks in the core beneath the ports. My rationale... I dive with a second and an octo so I have backup for the second stage but not the first. Of course my regs are virtually bullet proof despite diving frequently and hard over the past decade. If I get the bailout money I've applied for, I'll get all my regs serviced!