Mk10 IP Creep

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aquaregia

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Hi all,
Small background. Mk10 was working great, checked IP every month or so, one month I noticed it had a slow creep. This was after perhaps 18mo since the last service, perhaps 100 dives. Care was probably pretty average -- usually soaked after each dive, but a few times it got the 5min hose-down or worse.
So, I got a Mk10 kit and replaced the seat and all the orings provided in the kit (but none of the orings not provided, didn't think to buy those in advance). Gave everything a good teardown and clean in a sonicator with 50% vinegar, soft toothbrush for anything that looked a bit iffy (one of the shims looked to have iron rust on it) but mostly the ultrasonicator took care of almost everything. Was super careful with the piston the whole time -- didn't drop it, knife edge never touched anything other than water/vinegar mix.
Put it back together, with two shims was in the low 140s, but it was creeping still. Slower than before, perhaps 1psi/10s, but definitely creeping. I gave it about ten purges when I set it up before measuring to try to let stuff settle (is that enough?).
From what I can guess, it seems that creeping IP means damage in either the piston or the seat, which were the things I was super careful with. I spent some time dicking around with the stem oring, and I didn't replace some of the static orings, but I don't see how either of these could be related.
Could I have suffered piston damage while it was installed? From poor rinsing perhaps?
Cheers,
Andrew
 
I've found that some MK10s can creep a bit even with a new seat. The way I inspect the piston edge is with a 16X jeweler's loupe, and I have cleaned up the edge on some of them with a bit of micromesh wrapped around a tapered shaft. The ideal IMO would be a very fine conical abrasive stick. For significant dings you could 'lap sand' the edge itself by standing the piston, edge down, on a piece of micromesh glued or taped to a flat surface, then use the conical abrasive to clean and taper from the inside. I have noticed that scratches or dings that are too small to be visible can result in some creep. It must have to do with the relative size of the piston head to the shaft; on the MK5 the head is bigger so there's more force for a given IP. That doesn't mean that the seating force is higher; it's just counteracted with a stronger spring, but for some reason it does seem to result in less creep. Of the several Mk5s I've had, not a single one has ever creeped once I've rebuilt it. Most of my MK10s have creeped a few PSI until I cleaned up the piston edge. So you might try that, just be very careful.

If you leave it pressurized for several hours, maybe purging a few times every so often, the piston should form a more reliable impression in the seat, too. So try that first.
 
Slight thread creep; what grit of micro mesh do you use for polishing a piston edge? And where's a good place to buy an assortment pack?

I also looked for a conical abrasion stick, but didn't find anything that would seem to work size and grit wise.

I have a similar creep issue with an MK10.
 
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Before you go using any abrasives on the piston, why not try some "flitz" paste and a clean cotton face. cloth.
Polish the piston inside and out with the "Flitz" then wash it in simple green to take the residue off, lube it with crystolube and then try it.
Where did you get the I'M of 140 PSI?
I would do a check on that if I were you.

The IM on current models is 125-135 PSI, and the lower you can have it at the lower you can get the 2nd stage to crack at.
 
Slight thread creep; what grit of micro mesh do you use for polishing a piston edge? And where's a good place to buy an assortment pack?

I also looked for a conical abrasion stick, but didn't find anything that would seem to work size and grit wise.

I have a similar creep issue with an MK10.

Hi Henrik, I bought my set off eBay, like this one. I use most of the grits except the super-fine 12000, working my way up slowly. Depending on the size of the scratches, the coarsest 1500 may not be required. To clean the inside, I just roll a corner into a conical shape.
 
The IM on current models is 125-135 PSI, and the lower you can have it at the lower you can get the 2nd stage to crack at.

Care to explain this?

BTW, I believe the acceptable range for the MK10 IP is 125-150 PSI, according to scubapro.
 
1...the ultrasonicator took care of almost everything. Was super careful with the piston the whole time -- didn't drop it, knife edge never touched anything other than water/vinegar mix.
2...I gave it about ten purges (is that enough?).
3...the stem oring

1. I'm very wary of using an ultrasonic cleaner on the piston-not the main part just the knife edge. I keep it out of the solution for a couple of reasons. First, to prevent it touching other metal parts and hammering away at high frequency on the edge. The second reason may be unjustified, but the cavitation process that cleans away contaminates may actually dull the knife edge. (any comments correcting or confirming this theory are welcome.)

2. Maybe not. Try 20-30 full cycles. A full cycle is: air on-air off-purge. Remember, you want full travel of the piston.

3. The stem o-ring should not cause an IP issue if you used a high durometer (85-90) o-ring and liberally lubricated it.

@ Henrik Auto parts stores have packs of polishing sand papers that are suitable. They're not quite as high quality as a mico-mesh kit, but do just fine. (No pun intended)
 
Hi Henrik, I bought my set off eBay, like this one. I use most of the grits except the super-fine 12000, working my way up slowly. Depending on the size of the scratches, the coarsest 1500 may not be required. To clean the inside, I just roll a corner into a conical shape.

@ Henrik Auto parts stores have packs of polishing sand papers that are suitable. They're not quite as high quality as a mico-mesh kit, but do just fine. (No pun intended)

Thanks guys. I'll check it out.

Makes sense about just rolling a cone from the mesh/paper. I was thinking of wrapping the abrasive around the tip of a pencil or something similarly tapered. But it probably really doesn't much need much to get small nicks smoothed out.

---------- Post Merged at 10:34 AM ---------- Previous Post was at 10:28 AM ----------

1. I'm very wary of using an ultrasonic cleaner on the piston-not the main part just the knife edge. I keep it out of the solution for a couple of reasons. First, to prevent it touching other metal parts and hammering away at high frequency on the edge. The second reason may be unjustified, but the cavitation process that cleans away contaminates may actually dull the knife edge. (any comments correcting or confirming this theory are welcome.)

I can see your reasoning if you're using a solution such as vinegar, especially if it's fairly concentrated. No experience to confirm or correct though.

Someone mentioned testing out your ultrasonic and solution before using it on regulator parts: put a piece of aluminum foil in the ultrasonic and run it a minute at a time until you start to see tiny perforations. That'll give you a general (very general) idea of how "harsh" your solution and ultrasonic will be on the chrome, and you should probably stay a good margin away from this time/concentration "measure".

I would probably use a much less concentrated vinegar solution, and maybe even limit that to regulators with heavy deposits and corrosion. Otherwise Simple Green Crystal or Ivory soap seems to do the job.
 
Just fixed the quite high IP on my MK10. Checking the the piston edge with a 10x loupe, I could see - and then feel with a nail - a tiny nick in the edge. I used Micro Mesh to 1) ever so slightly sand the "top" of the edge - basically placed the piston upright and very gently and carefully moved it across the Micro Mesh 2) rolled the Micro Mesh into a cone that I fit into the piston, and by rotating the piston, slightly buffed the inside edge 3) very gently buffed the whole outside of the piston stem, leaving a tiny bit of "scuffed" finish to better retain lubricant.

IP is now a solid 140 psi and locks up with just a tiny bit (~2-3 psi) of creep within the first second after a purge.

The reg will now be back in service as deco/stage reg along with a ragged looking but perfectly functioning G250 :)

Feels great when it works out that way.

Now I should get the very old MK3 rebuilt for shop air :)
 
I gave mine a ton of purges, left it pressurized overnight then did four dives on it. IP seems much more stable now -- looks locked according to my cheap IP gauge, but don't currently have access to a quality one to verify.
 

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