SP MK 10 PLUS: please help ID

[Texfrazer]

Zung,

No worries. I have been busy with work and have not had a chance to go get some.

I'm glad you've found a supplier that's almost on the continent.

Happy sanding/buffing!

Tex

 

[Zung]

I'm not sure if the Brits agree to that

 

[Couv]

I agree that you probably have a small nick or scratch on the piston stem end. However, one thing that could be throwing you a curve ball is the gauge orifice. I made an IP tester and was getting a few strange readings, then things would settle down. It turned out that the orifice in the bottom of the gauge was small (to protect the gauge from shock) and was only allowing the IP to indicate slowly. I drilled out the orifice and now it works just fine.

c

 

[redacted]

I agree that you probably have a small nick or scratch on the piston stem end. However, one thing that could be throwing you a curve ball is the gauge orifice. I made an IP tester and was getting a few strange readings, then things would settle down. It turned out that the orifice in the bottom of the gauge was small (to protect the gauge from shock) and was only allowing the IP to indicate slowly. I drilled out the orifice and now it works just fine.

c

Interesting point. I am surprised at how little IP drop Zung reports when the reg is purged. My Mk5s and 10s all drop from about 125-130 psi to about 90 psi when purged. That opening is one thing that could effect the responsiveness of the gauge.

 

[halocline]

A few years back I started a thread about IP drop with various first stages, and there were things happening with IP drop that I couldn't figure out, and nobody else could either. I agree that there is likely to be lots of variation from one IP gauge to the next, and I think there's also variation depending on where the IP gauge is located. If it's on a LP inflator hose, like mine is, there could easily be a venturi effect in the IP chamber when air starts flowing into one LP port, causing a momentary pressure drop in the others.

Totally off subject, but I have apparently found some MK10 SPEC boots, finally!! Now I can pack my MK10s and dive carefree in the frigid waters around here.

 

[Zung]

Interesting point. I am surprised at how little IP drop Zung reports when the reg is purged. My Mk5s and 10s all drop from about 125-130 psi to about 90 psi when purged. That opening is one thing that could effect the responsiveness of the gauge.

Wrong lead, my bad, sorry.

I live in a residential area and I do most of the work in the evening or at night, so I rarely if ever do a full sustained purge to avoid annoying the neighbours. In a quiet place, a full purge is LOUD! On top of that, I'm cheap and I try to make a tank last as long as I can. So the "drops" I reported are more like what happens after a deep breath or a light purge. If you guys think it's important to measure the full drop, I can go to the dive club and do a real blast from there.

The gauge itself should be OK: for a starter, I didn't make it, I paid 30 bucks for it at a shop, so it must be good, right? The other thing is, I always get some pretty credible ranges and distributions from that gauge, like IP from 1 unit at 120, through 3 units at 130 PSI to 2 units at 150 PSI; and the IP recovery (after a light purge) from less than a second (3 units) to several minutes (3 units). And the readings are pretty reproductible too.

I set aside this weekend to work on mattboy's secret receipe.

I got myself a decent 20x loupe and checked the brass piston I removed from my #3 MK10 (ex-)Plus, the one which started this thread. The knife edge is horribly scratched, and the part of the stem which is not chrome plated has many tiny pits. I'll see if I can find a way to take a picture of it.

OTOH, I looked long and hard at the stainless steel shaft from the composite piston I removed from my #2 MK20, I can only find 1 light scratch on the body about 2mm from the knife edge and about 5mm long, plus some roughness on some parts of the knife edge and the body. But then again, when I compare it against a brand new piston I have, the wear & tear are very obvious.

 

[Couv]

This is a long thread, so please forgive me if we've covered this already. I am wondering if you have taken the time to properly cycle your first stages. The idea is to engrave the first stage seat deep enough to get a good seal. It usually takes 20 or more cycles to do that and should be done before you start testing the IP. To save air, remove all hoses except the one connected to the second stage you will be using to purge. Alternatively, I think you may be able to leave a reg pressurized for a long time (24 hours) to allow the seat to settle....I have not tried that method.

One other thing while I'm thinking about it. Have you checked to see if your piston is bent? If it is, then it is likely not to be mating with the HP seat squarely.

....this is more fun than working on it myself....

c

 

[Zung]

Yep, it's a long thread; maybe I should start a new one to tell my experiments with mattboy's secret receipe.

To recap:

1. MK10 (ex-)Plus #1, the one that started this thread: downgraded to MK10, new seat, dutifully cycled 20-30 times, added an extra shim, pressurized overnight, IP is 123 PSI and rock solid. Case closed.
2. MK10 Plus #2: replaced all o-rings, new seat, cycled a few times, IP is 133 PSI, rock solid. Case closed.
3. MK10 Plus #3: replaced the seat with a like-new one, cycled 20-30 times, but IP still creeps to 150 PSI. This is the rogue one; it has a stainless steel piston, but its lineage is suspect: ex-rental from a dive shop that closed down. I paid for an upgrade to "Plus" about 10 years ago and it sat in a closet until last year.

So the #3 is the one I'll try mattboy's magic on. I'll try my hands on the "Plus" brass piston I removed from #1 because it's all messed up anyway. And that's why it's confusing. I'll check to see if the SS piston is bent.

Another thing worth pointing out is the #2 still is a *Plus*, and it's not all bad: instant lock up, no creep.

 

[Zung]

One other thing while I'm thinking about it. Have you checked to see if your piston is bent? If it is, then it is likely not to be mating with the HP seat squarely.

As far as the naked eyes can tell, the piston is true: I spinned it around a stick.
I also looked at the knife edge with a 20x loupe, there are some tiny little nicks. I tried to take a picture, but the nicks don't show.

The numbers for this reg are:
Deep inhale: 110 PSI
1 sec.: 125
5 min.: 139
10 min.: 142
15 min.: 146

I'll wait until the micro-mesh come and I'll give it a try.

 

[Couv]

Perhaps it due to the magnification, but that does not look like a knife edge to me. It looks to be on the square side…..better do as Dr. Matt says.