Main spring sag...

[axxel57]

Been overhauling a couple of Atomic Z2 first stages... one had some rust pits in the main spring I didn't like the look of so got a new one.

Comparing new to old it was immediately apparent how much the old one had sagged over a decade or so!
New vs Old
View attachment 444475
New 28.50mm
Good used 27.75mm
Old 25.80mm

I'm pretty sure that in another 'spring thread' here somebody mentioned that some springs getting stiffer is caused by getting shorter with time and usage......

 

[halocline]

Regardless of the details about springs shortening and/or stiffening over time, I think it's not a bad idea for we MK5/10 owners to find a good source of new springs. Most of mine have IP down on the lower end (125PSI) which is fine with me, but that's with the short seat that raises IP. It makes sense that the springs would wear out enough to not really function as well as new, resulting in lower and/or unstable IP. I have a small stash of NOS springs, and they've livened up a few of my MK10s.

I've had great results replacing the 2nd stage springs on the G250/balanced adjustable; in fact, it helps the tuning so much that I simply replace the springs anytime I get a new-to-me 2nd stage and rebuild it.

 

[Fibonacci]

If you can measure ALL of your NOS spring stash (free length, pitch, space between coils, number of full coils, outside diameter, wire diameter) we can establish a base data set. The spring rate is the most critical which is the amount of force required to move the spring 1mm of distance, which would need to be measured from all your NOS springs and a Median rate determined... a spring manufacturer would have suitable test equipment.

Having established the specifications, it would not be difficult to get a run of springs made in a grade of stainless steel suitable for marine use. There are pros and cons for 302, 316 and 17-4 PH steel grades, but they should all be passivated after forming for maximum corrosion resistance.

There's a couple of interesting articles with much more detail incl an auto quote facility here:
Stainless Steel - Coil Spring Design - Specialty Springs
http://leespring.com/downloads/uk/leespring_engguide.pdf

Custom Compression Springs | W.B. Jones Spring Company
How to measure springs video:

Then finally there is the small matter of liability for the US market to be sorted out... maybe approach VDH who have been down this path before

 

[Fibonacci]

I've had great results replacing the 2nd stage springs on the G250/balanced adjustable; in fact, it helps the tuning so much that I simply replace the springs anytime I get a new-to-me 2nd stage and rebuild it.

Good timing!
I compared a G250 Graphite I had just finished fully rebuilding (apparently been for a drink and stored wet, so had to recut the heavily corroded adjuster knob and orifice threads inside the air tube with 1/2" x 20 UNF and 5/16" x 32 UNEF taps) fitted with old and new springs.
Big difference indeed... much more responsive with a new spring!
Now I will have to retrofit new springs into my other three just-rebuilt G250's

 

[lexvil]

A follow up;

I pulled the piston and inspected it with a 16x loupe and didn’t see and overt signs of wear or cutting so reassembled and tested, lock at 145 as before which is still at the upper end of spec so, I looked at the seat with the loupe and it was ratty looking. I have a bag full of used atomic seats so I looked at those and all have a clear defined line or lip on the sealing surface, clean and sharp so I tried those, each resulted in IP’s ranging from 150 to 180, all on the same tank with 3400 psi. Before putting it away in the parts box I put the original seat back in and now it’s running a crisp no creep 135 IP! Leaving for Hawaii on Sunday so I may take this along to see if it holds up on a few dives.

I don’t think this one off regulator proves anything but it is interesting or maybe baffling.

 

[Fibonacci]

Hmm... interesting!

Did you lubricate the piston stem or bore more the second time?
Or is part #01-0026-00 Back Up Ring, Teflon worn or distorted?

I just rebuilt a USD Conshelf IV with OEM parts but struck an annoying IP problem as it was like new inside, no nicks or marks on the machined-in-body HP orifice.
It would snap promptly to 125 psi then slowly creep from 125 to 145... bugged me bigly so I pulled it partially down again and put a tiny bit of lube on the push pin shaft and changed the backup washer from split to dished solid type in the crown.

Reassembled with no other changes and it snapped to 125 psi and stayed rock steady ever since!

 

[rsingler]

@lexvil Can I ask for a bit more detail?
When you say, used seats with IP's ranging from 150-180, what gauge behavior did you see?
Initial slowing ~135, then slow bleed up to 150-180? Then lockup? Or crisp lockup with each seat, but at a variety of different pressures? Did the 180psi seat continue to creep?
Or some of each, depending upon the seat?

 

[lexvil]

@lexvil Can I ask for a bit more detail?
When you say, used seats with IP's ranging from 150-180, what gauge behavior did you see?
Initial slowing ~135, then slow bleed up to 150-180? Then lockup? Or crisp lockup with each seat, but at a variety of different pressures? Did the 180psi seat continue to creep?
Or some of each, depending upon the seat?

Some of each, even the highest locked and didn’t go further, I left them under pressure for several hours and tapped the purge every so often, breathed it too. One popped to 125 and started creeping right away locking about 150.

 

[lexvil]

Did you lubricate the piston stem or bore more the second time?
Or is part #01-0026-00 Back Up Ring, Teflon worn or distorted?

I just rebuilt a USD Conshelf IV with OEM parts but struck an annoying IP problem as it was like new inside, no nicks or marks on the machined-in-body HP orifice.
It would snap promptly to 125 psi then slowly creep from 125 to 145... bugged me bigly so I pulled it partially down again and put a tiny bit of lube on the push pin shaft and changed the backup washer from split to dished solid type in the crown.

Reassembled with no other changes and it snapped to 125 psi and stayed rock steady ever since![/QUOTE]
Slightly less lube if anything, I did wipe it off before checking the edge and did re-lube it lightly.

 

[rsingler]

Some of each, even the highest locked and didn’t go further, I left them under pressure for several hours and tapped the purge every so often, breathed it too. One popped to 125 and started creeping right away locking about 150.

Well, that makes more sense. Any imperfection in the seat was malleable, to a greater or lesser degree, as the piston came in contact with it. Whatever tiny gap remained, either in the knife edge or the seat, or both, was obliterated as the seat molded slightly. IP continues to climb during that molding process, and creep stops when there's a mating seal between the imperfect parts.
Therefore, I expect it will be easier to find the flaw in the seat that went to 180 psi, than in the one that locked up quickly.
From a diving standpoint, the risk is not in the early IP creep, because that goes away with every breath. The problem starts when the regulators sit pressurized (i.e., on the side of a boat on the way to a dive site), and the second stage starts to freeflow when the IP exceeds its limit. Obviously, balanced seconds will be more tolerant of this than unbalanced.
Newer-material seats can go for years without a leak, and the only deterioration might be in the dynamic o-rings that might necessitate service.
So if you've found a seat that works, hang onto it.
That said, I do regularly see tiny pitting (sandblasting) in the sidewall and knife edge of pistons where they get "dirty air". That may be nothing more than tiny salt crystals and dust blown at 3000 psi through a green sintered metal filter, because a diver isn't careful about drying and capping his first stage in between tanks. As @halocline noted, a little polishing will often do the trick. But it's not 600 grit from the hardware store. For me, it's flat pieces of 3,000 to 8,000 grit Micromesh on the work table, and the piston spun with your finger holding onto a 5/32" hex key threaded down the middle as you successively increase the fineness of the grit. Only takes 5 minutes.
I'm just careful to handle both pistons and seats like the fragile items they are. They get wrapped and set aside until I'm ready to install them. A thousandth of an inch scratch, and you have IP creep.

Glad you got a good lockup!