Main spring sag...

[Fibonacci]

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

New 28.50mm
Good used 27.75mm
Old 25.80mm

 

[chris kippax]

Wow that is a lot! In mechanics we usually measure springs under a specific load which I imagine the one pictured would perform be even worse.

 

[Fibonacci]

Yes 2.7mm is a lot!
Usually there is a minimum length under a specific load specification... but seems not so for SCUBA applications.
Just a minimum IP under a maximum of three shims... seems odd for such a critical spring!

 

[lexvil]

Just for the sake of knowing can you do a quick test with each spring to see what the IP is?

 

[Fibonacci]

Will do so on the weekend, final parts arrived yesterday... I'm keen to know too.
FWIW the Z2 with the good used spring (free length 27.75mm or 0.75mm sag vs new) lubricated with Tribolube 71 had 125psi IP with two new shims as supplied in the Atomic overhaul kit.

 

[Fibonacci]

OK back from the tests... rather surprising results!
Old spring, 2 new shims, new seat and seals lubricated with Tribolube 71
IP 120psi creeping slightly to 125psi then stable.
New spring 2 shims other details as above
IP 115psi
Extra shim installed IP 120psi and stable.
Also rechecked part numbers... Atomic list the same number for the spring across all their regulators 21-0570-00

Strange I would have thought exactly the opposite would have happened... and yes I did check to ensure I hadn't mixed up the springs!

 

[lexvil]

Interesting

 

[Couv]

OK back from the tests... rather surprising results!
Old spring, 2 new shims, new seat and seals lubricated with Tribolube 71
IP 120psi creeping slightly to 125psi then stable.
New spring 2 shims other details as above
IP 115psi
Extra shim installed IP 120psi and stable.
Also rechecked part numbers... Atomic list the same number for the spring across all their regulators 21-0570-00

Strange I would have thought exactly the opposite would have happened... and yes I did check to ensure I hadn't mixed up the springs!

Surprising in that the new spring is longer than the old spring. However, if one ignores the difference in length, not surprising because as springs age they tend to get stiffer.

 

[Fibonacci]

Seems Atomic had a recall due to main springs breaking way back in 2001...
CPSC, Atomic Aquatics Announce Recall of Scuba Regulators
Atomic Aquatics has received 14 reports of regulator springs breaking, four of which occurred while the scuba equipment was in use. No injuries have been reported.
For only $16, a new main spring when rebuilding older Atomic first stages is good insurance IMO

 

[lexvil]

I just got a Z2 in with a long creep to 160 psi, spring is 27.5mm two shims. It’s drying right now but will lightly lube everything and put it back together just to see what happens.