Unexpected IP drift in a newly-serviced first stage

[BoltSnap]

To answer your specific question, I don't see enough SS pistons compared with Monel to give you an abrasion resistance answer. But if you own an Atomic with a SS piston, just watch for IP drift. If it doesn't start to appear, you either have really clean gas and tanks, or maybe SS is better in this regard. Time will tell.

I have had my ST1 since circa 2012. It is my "go to" regulator for recreational diving (I still use other brands/models to test but it is my go to regulator). I have only serviced it once since 2012. No corrosion or any issues with drifting or anything at all. I have traveled with it to third world countries and got my fills everywhere. I have had my B2 (was B1) since circa 1997 and was serviced every 5 - 6 years and never an issue. It was my primary regulator from circa 1997 to 2012 when I got my ST1. No issues with drifting or anything either.

 

[Geo7]

While it is a "submarine" metal, supposedly much more resistant to moving salt water corrosion than other stainless steels, it is definitely susceptible to corrosion under trapped salt water. There's a metallurgical term for that, that I can't recall, but hopefully an expert can enlighten us.

The specs for Monel alloys call it "crevice corrosion".

Also, monel will cause steel to corrode if in contact with monel.

The good news is that monel parts polish to like new condition very nicely (following rsingler's method).

 

[Geo7]

Here's an example of a Monel piston from a guy in the tropics who regularly got wet fills or was sloppy at tank changes.

Out of curiosity: Does the verdigris on Monel come off in the ultrasonic bath? I feel that I don't need ultrasonic since I don't need nitrox cleaning, and my regs are titanium so they need very litle cleaning.

When I had Monel parts that were green, they returned to a super shiny surface poishing them with micromesh for a few minutes like you explained in other threads. I have steel pistons in mine now, but it's gonna be a year or two until they are up for service. If the steel holds up I might miss working on the Monel as it is quite Zen...

 

[Yellowdog]

Stainless Steel 1st stage parts weigh more ( cost less ) than the same monel parts but may be more corrosion resistant. The ss piston may be more resistant to dings or nicks but still to be determined. A ss piston, swivel retainer and or seat retainer used in a titanium first stage would not change the "Nitrox ready – approved for non-dedicated EAN use with mixtures up to 40%". Stainless Steel is not as sexy as monel but may have some practical benefits in the sometimes harsh first stage regulator environment. Do I understand correctly or have I missed it entirely?

 

[Geo7]

That sounds about right for a summary, though I think replacing monel parts for steel and titanium would downgrade a T3/T2X reg to T2 or even T1X level, and if going by manufacturing specs that would lose the non-dedicated nitrox rating. That's what I chose though: upgraded T1X.

If serviced regularly, the Monel polishes out to like-new finish easily. Granted, a standard dive shop won't spend the time restoring these parts (or may not even know this "lost art"), but I'd hope they'll just use the lifetime warranty and put in a new Monel part. Can someone confirm this? If the lifetime warranty applies, then a typical customer should just go for modern models with Monel parts and forget about this whole issue.

For DIY owners the dilemma when overhauling a neglected reg remains. I think we may see different types of corrosion in steel vs monel. Perhaps a 316 steel piston might also see some surface rust, and I don't know if that'll be as easy to deal with. But no one reported any issues (see Boltsnap's earlier post).

 

[lexvil]

Monel;

Monel - Wikipedia

en.wikipedia.org

it’s used heavily in U.S. Submarines (or was) for corrosion resistance, in the machine shop parlance there was “regular“ Monel which is silvery and “K” Monel which was more red.

 

[rsingler]

Does the verdigris on Monel come off in the ultrasonic bath? I feel that I don't need ultrasonic since I don't need nitrox cleaning, and my regs are titanium so they need very litle cleaning.

When I had Monel parts that were green, they returned to a super shiny surface poishing them with micromesh...

I have found consistently that although the surface verdigris can be removed, it is much like chromed brass in contour: what is left behind is a shallow pit. Here's a terrible example of Monel shaft pitting corrosion after attempted restoration:

This piston was replaced. Pretty disappointing for "corrosion-proof" submarine metal.

If it's a sealing surface, restoration requires taking off adjacent metal until the line of seal is restored. On a knife edge, that shortens the piston by a few thousandths of an inch each time.
When it happens on a shaft due to an unsealed piston left unrinsed and wet, or one that had a bubble in a Tribolube fill that was replaced by seawater, it risks an HP o-ring leak that once again displaces lube or leaks air on a dive - a straight road to valve failure.

I don't know how @BoltSnap has such consistently stable regs. The stuff I get into my shop must be unusual. He is doubtlessly blessed.
Here's an Atomic with clear voids in the fill which had been replaced by seawater:

The piston shaft was pitted everywhere

But worse was the crevice corrosion (thank you, @Geo7 !) on his knife edge:

Just for grins, I tried to restore it, but could not get to the base of the crevice where it crossed the knife edge sealing line:

Obviously, this guy had to buy a new piston, too

IMO, the jury is still out on Atomic's Monel pistons...

 

[BoltSnap]

I have found consistently that although the surface verdigris can be removed, it is much like chromed brass in contour: what is left behind is a shallow pit. Here's a terrible example of Monel shaft pitting corrosion after attempted restoration:
View attachment 811298
This piston was replaced.

If it's a sealing surface, restoration requires taking off adjacent metal until the line is seal is restored. On a knife edge, that shortens the piston by a few thousandths of an inch each time.
When it happens on a shaft due to an unsealed piston left unrinsed and wet, or had a bubble in a Tribolube fill that was replaced by seawater, it risks a HP o-ring leak that once again displaces lube or leaks air on a dive - a straight road to valve failure.

I don't know how @BoltSnap has such consistently stable regs. The stuff I get into my shop must be unusual. He is doubtlessly blessed.
Here's an Atomic with clear voids in the fill which had been replaced by seawater:
View attachment 811293
The piston shaft was pitted everywhere
View attachment 811292
But worse was this example of crevice corrosion (thank you, @Geo7 !) on the knife edge:
View attachment 811290
Just for grins, I tried to restore it, but could not get to the base of the crevice where it crossed the knife edge sealing line:
View attachment 811291
Obviously, this guy had to buy a new piston, too

IMO, the jury is still out on Atomic's Monel pistons...

In my experience, Atomic regulators have been the most reliable and trouble free compared with other brands I have used for my personal diving and/or for dive center; Mares, AL, Scubapro, Cressi, Seacsub, etc. I have tried most brands that have international presence. I have Z2's in the training fleet. Scubapro can take 3 - 4 years between servicing, Mares, Cressi and Seacsub 1 - 2 years. AL perhaps 3 years but I haven't used too many of AL regulators to judge. Up until COVID, I used to teach several courses during the year but I have slowed down teaching since COVID but do more "fun" diving with my friends/former students now. I test all of my regulators, personal and rental, on frequent basis.

 

[Nemrod]

I am very much intrinsically opposed to using silicone or any other grease to pack a piston regulator ambient chamber. All that is going to happen, sooner or later, is that it will be intruded by and/or diluted by seawater. And then it traps the seawater adjacent to the metal where any impurity in the metal results in corrosion. It is just a bad idea. A better thing is to have large ambient chamber holes to make rinsing easy, drying easy and seawater retention unlikely. Yes, bad stuff could go in but just as easy the bad stuff can go back out either of it's own accord or my assistance in the rinse.

 

[lexvil]

I am very much intrinsically opposed to using silicone or any other grease to pack a piston regulator ambient chamber. All that is going to happen, sooner or later, is that it will be intruded by and/or diluted by seawater. And then it traps the seawater adjacent to the metal where any impurity in the metal results in corrosion. It is just a bad idea. A better thing is to have large ambient chamber holes to make rinsing easy, drying easy and seawater retention unlikely. Yes, bad stuff could go in but just as easy the bad stuff can go back out either of it's own accord or my assistance in the rinse.

Or better yet a Sherwood SR first and even better a diaphragm. It hard to rinse the micro abrasives (especially for shore dives) out of an unsealed piston with some of it getting trapped in the lube on the piston seal, it does take a long time for the damage to cause issues but that is true in either case.