SP MK-20 - IP Creep

[buddhasummer]

Am wondering if this high ip was why when I disassembled the reg it had no spring centering washer but two shims instead. I'm guessing I need to leave something in there so the spring isn't in direct contact with the body?

 

[buddhasummer]

It's crept another couple of psi but could well just be settling as it's a new seat. I'll leave pressurized overnight.

 

[fmerkel]

I sympathize with your frustration. My wife's MK20 is like this on some overhauls. I have 3 pistons to swap around one that I did the polishing on. Seems I always have to assemble it 3-4 different ways to deal with the creep or with whistling/honking. Once I get it, it's pretty solid until the next time. Personally I think the piston stem shim setup is kind of unstable and contributes to the problem.It's the only reg we have that does this.

Oh, and it seems to 'eat' piston O-rings. They get nibbled on. I do use the 90 duro. I'm going to try polyurethane-90 next build.

 

[buddhasummer]

I'll give it one or two more rounds then I'll concede defeat. I wouldn't have thought it would be this finicky.

 

[buddhasummer]

I sympathize with your frustration. My wife's MK20 is like this on some overhauls. I have 3 pistons to swap around one that I did the polishing on. Seems I always have to assemble it 3-4 different ways to deal with the creep or with whistling/honking. Once I get it, it's pretty solid until the next time. Personally I think the piston stem shim setup is kind of unstable and contributes to the problem.It's the only reg we have that does this.

Oh, and it seems to 'eat' piston O-rings. They get nibbled on. I do use the 90 duro. I'm going to try polyurethane-90 next build.

How long between it needing servicing? Cheers.

 

[fmerkel]

She does ~60-100 dives/year. I generally let it go a year unless I see the telltale occasional bubble out of the ambient chamber indicating the O-ring is going. This last time I checked it after a 30 dive Philippines trip. The IP had gone up (?) to ~150 but was stable. I found the piston O-ring nibbled on but not yet leaking. Pulled 2 shims, cleaned it up and only replaced the piston O-ring (stock SP). Pretty solid IP ~130 this time but it whistled a little. Luckily that went away after some cycling and she hasn't told me it's an issue diving. I'm happy with 130 as we dive cold most of the time.

Last build I had some challenges getting the IP to behave, AND the whistling wouldn't go away until I swapped out the piston, seat, and O-ring shims. I let her dive it a couple times to see if it would settle down but it would not and she was not happy with the noise on a dive. I lubed it plenty (Cristo) and do use an insertion bullet thinking maybe I was doing the O-ring damage. Oddly I inserted the piston for years sans bullet without ever nicking anything.

Have you noticed there is a fair amount of discussion about IP creep in the MK20? Every other piston I have (Sherwood, Oceanic) I just put them together and they work. No fuss at all.

 

[guruboy]

The newer composite piston is supposed to have solved the IP creep issue.

 

[rhwestfall]

well, I went back to the beginning of this thread, realizing I was the one who started it (forgot I even did this)...

For me, two of my 3 MK-20 stages had the "brass tipped" middle generation piston, this being one of them. I was able to procure two composite pistons, and swapped them out. As the regs had a total of 1 dive on them, and had been sitting, there was no issue with mating the new stem to the existing seat, and things are much better in regard to stability/lock up. An interesting side note is that both stages have had a significant drop in IP (stable & locked) with the composite piston. I actually need to shim them as they are in the low end of the specification now.

I just picked up a 4th MK-20, and have not opened it yet to see what is inside it...

 

[buddhasummer]

The mystery continues, woke up this morning and ip had dropped almost 15psi. No idea what's going on. Oh well at least it's now at mid range 135. I'll dive it and see what happens after a dive.

So far, I've used two different pistons, 2 different seats and 3 pistonstrn O rings, return for effort is not looking good at this stage.

Got all keen and bought a lot of MK10 Plus spares in anticipation of using this reg, at least most, save seats, seat retainer and piston can be used in a MK10.

 

[buddhasummer]

She does ~60-100 dives/year. I generally let it go a year unless I see the telltale occasional bubble out of the ambient chamber indicating the O-ring is going. This last time I checked it after a 30 dive Philippines trip. The IP had gone up (?) to ~150 but was stable. I found the piston O-ring nibbled on but not yet leaking. Pulled 2 shims, cleaned it up and only replaced the piston O-ring (stock SP). Pretty solid IP ~130 this time but it whistled a little. Luckily that went away after some cycling and she hasn't told me it's an issue diving. I'm happy with 130 as we dive cold most of the time.

Last build I had some challenges getting the IP to behave, AND the whistling wouldn't go away until I swapped out the piston, seat, and O-ring shims. I let her dive it a couple times to see if it would settle down but it would not and she was not happy with the noise on a dive. I lubed it plenty (Cristo) and do use an insertion bullet thinking maybe I was doing the O-ring damage. Oddly I inserted the piston for years sans bullet without ever nicking anything.

Have you noticed there is a fair amount of discussion about IP creep in the MK20? Every other piston I have (Sherwood, Oceanic) I just put them together and they work. No fuss at all.

Yes, read about ip isssues on the MK20 early piston regs and the MK10 Plus. Should have taken heed and avoided getting into this reg. I can see diaphragm regs exclusively in my future. I'll continue to try and sort this MK10 Plus out, will dive my other standard MK10 for a season and re evaluate my position, maybe piston reg DIY is not for me.