Scubapro piston: is there a life after death?

[Zung]

Certainly I've seen MK25s that have zero creep and zero evidence of wear in the seat after a few seasons of diving.

That's interesting, mattboy, can you elaborate please? Are you talking about casual divers/tourists with less than 50 dives a year, or DM's/instructors with more than 100/year? And "few" means 2 to 5, right?

I'm almost done with servicing my gears, and I'm looking for guidances for the future. DA once said because of the plastic bushing system, the intervals of the MK20/25 may not be as great as those of the MK5/10.

 

[halocline]

I don't know, maybe 100 dives total. But that's ZERO creep. There was an instructor in Roatan using a MK25 every day, several dives, for a couple of seasons and he asked me to rebuild it; it had no creep but high IP, I think about 160.

Thinking about it, I can't remember ever having any creep in my MK5s either, once I've rebuilt them. I just end up servicing them at some point when I feel like it. I have occasionally noticed some creeping in my MK10s if I don't use them for a month or more; usually a dive brings them back to zero or very slight creep, but they get rebuilt more often. I have one MK5 that I use a lot and it's been a couple years; every so often I put an IP gauge on it and it's rock solid at 125.

I only own one reg with the bushings, a MK15, so I'm not as familiar with the way the bushing system wears. But, the stress is on the HP o-ring, not the bushings, and the bushings are supposed to reduce stress on the o-ring. Between that and the round edge on the piston, I'd bet that the MK25 can go a longer time than MK5/10s on average.

 

[redacted]

I have serviced my wife's Mk20 twice in the last 10 years due to IP creep. I suspect the culprit is dirt and deposits on the seating surfaces rather than seat wear like with the cave cone seat and sharp, knife edge pistons. Maybe next time, I'll just clean the seat and piston and see if that restores IP stability. Do you think she will mind???:blinking:

 

[Zung]

Thank you for your inputs.
Let's see:

• No creep after 100 dives
• 2 seasons in Roatan; assuming 100 days/season and 3 dives/day, that's 600 dives.
• 2 services in 10 years, so that's 1 every 3 years

So about 150 dives and/or 3 years service intervals seem to be reasonable.

It's also true that the piston doesn't mark the seat that much: I replaced the piston on my MK25 #3 without even touching the seat, and it doesn't mind at all, and I'm doing exactly the same to my MK20 #4. So awap's idea seems to be workable: take it apart once in a while, clean it up and call it good.

 

[Zung]

On to the last one: I'm not gonna bore you with the details, it's almost a carbon copy of Case 2, except I got lazy and didn't completely remove 1 patch of extremely fine scratches. Results:

• Before: 1 minute recovery
• After: a bit over 1 second, maybe 1.5 sec, and a solid lockup at 9.5 bar / 138 PSI

The lockup is not as snappy as the other ones but still is plenty good enough. It may or may not relate to the leftover scratches, or it just requires a bit more time to set in, I did this a few hours ago.

The moral of the story is:

• Buying new is cool: I have 2 regs bought new I never have any problems with.
• Buying used could be cool, or could cost you a piston if you do things by the book.
• Recalling a piston from the deads is not a big deal: about a hour's work max, and 10 bucks' worth of Micro-Mesh. So far, it's 3 successes out of 3 cases.

Of course you shouldn't be doing this yourself, it's life support, bla, bla .

Edit
After a night's rest, the thing has decided to settle for 9.4 bar / 136 PSI. Fine by me.

 

[Zung]

Maybe next time, I'll just clean the seat and piston and see if that restores IP stability. Do you think she will mind???:blinking:

You're on the way to become a real professional, Gary, but you're not there yet: take the reg to the back, rinse it off, charge $70. That'll get you your final certificate.

 

[Couv]

…..but don't forget to put a few scratches on the chrome and over torque each hose at the first stage.

Thanks for your updates Zung.

c

 

[Zung]

…..but don't forget to put a few scratches on the chrome and over torque each hose at the first stage. c

Wow! That some serious attention to details! But it's a bit time consuming and I doubt he'll ever win that "Most Profitable Tech In Town" medal with that. Maybe just a quick beat up with a baseball bat?