'Vintage' piston 1st-stage main springs, is there a danger of metal fatigue/spring snapping in two?

[scubafanatic]

I remember reading a while back that old piston 1st-stage regs experience their main springs becoming stiffer, as if the steel they're composed of somehow 'ages' and becomes stiffer, but I was wondering if the metal becomes more brittle and at risk for snapping in two as the reg ages ?

I've got a large number of Scubapro MK-5's and was curious if this is a potential issue with such 'vintage' regs ?

 

[Fibonacci]

All springs will eventually either sag and/or work harden and become a bit stiffer... generally speaking a catastrophic failure usually needs to propagate from a stress riser like a rust pit or deep nick. Sagging is far more common IMO.

I was overhauling a Sea Hornet Mk V which had not been rinsed off properly and then stored for many years... the spring recess was a mass of rusticles and the spring came out in two pieces, having failed at a deep rust pit near the ground and closed end

For regs that still have widely available new parts (like Atomic) I routinely replace the first stage springs if they have sagged more than 1mm from new height. At $17 each it is a cheap insurance policy!
Check this thread:
Main spring sag...

With a vintage MK 5 if you can't get them brand new from Scubapro or vintage NOS I would look at each one very closely for rust pits or nicks before re-using.

 

[tbone1004]

like @Fibonacci said, it's not age, it's use that will cause them to stiffen. Breaking is not something I'd worry about

 

[Couv]

I've never seen it personally, but I do remember reading about a MK10 spring breaking.
I can't get the IP to stabilize - Vintage Double Hose

 

[tbone1004]

@couv looking at that, how much was abuse due to that corrosion?

 

[Couv]

Yes, it looks pretty nasty, but I don't know the history. Who knows what the owner did prior to sending it to Bryan? I would like to see the edges where the break occurred to see if it was a clean break or signs of corrosion. From what we can see, my bet is on corrosion.

 

[northernone]

Small data point here.

Never seen one snapped without bad rust, they seem to just sag or stiffen.

I've opened one that had a nondescript rust/dust conglomerate where the spring use to be. It was brought up off the seafloor.

Cameron

 

[tbone1004]

Yes, it looks pretty nasty, but I don't know the history. Who knows what the owner did prior to sending it to Bryan? I would like to see the edges where the break occurred to see if it was a clean break or signs of corrosion. From what we can see, my bet is on corrosion.

@Bryan@Vintage Double Hose care to weigh in on that one?

@herman or @Luis H have you guys seen a break like that?

 

[Bryan@Vintage Double Hose]

The majority of springs on MK 5's and 10's I work on have a some surface rust where the spring touches the piston base but 99% of the time it cleans up with a brass wire wheel or a green pad.
I have had several springs that have just gone soft and replacements had to be sourced.
This its the only SP spring in my recollection that was BROKEN.
But diagnosing the reason the IP was unstable was pretty easy in this case

 

[Couv]

This its the only SP spring in my recollection that was BROKEN.

Do you remember if inside the break if it was shiny or discolored or a combination of both? All shiny indicates a clean break, combination points to corrosion that weakened the spring until it broke, completely discolored does not tell much as it could have been snapped and left that way, then corroded after the fact.