SP MK-20 - IP Creep

[buddhasummer]

Is it leaking from the ambient ports?

If it is, I can't hear it. I cannot submerge it to check.

 

[Couv]

You don't need to turn the tank off. Just "breathe" off the reg to cycle the piston.

The Usual Suspects are split on this issue. IIRC Zung likes to break a seat in by leaving the first stage pressurized for an extended period of time. I like to cycle in just the way described. Air on/air off/purge = 1 cycle. I like to do this at least 20 times. Awap enjoys irritating his lovely wife while she watches her favorite TV show by tapping the purge button a few million times with the pressure still on. pssst, pssst, pssst, pssst, pssst, pssst, pssst, pssst, pssst, pssst, pssst, pssst. We are all happy with our results, so whatever works.

Having said that, as I look at the design of the MK20/25 & MK10 Plus that have a more robust soft seat and a less sharp piston edge, I wonder if breaking in is necessary, and if so, which method would work best.

 

[Couv]

Guru said, "Is it leaking from the ambient ports?"

If it is, I can't hear it. I cannot submerge it to check.

Try putting electrical tape over the ambient chamber holes and let the first stage sit pressurized for a few hours. If there is a leak in the ambient chamber, a bubble will form in the tape.

I've found that the most likely cause of erratic IP is a problem with the seat. Perhaps dirt or a scratch or miss matched engraving. The easiest thing to try is a new seat; if that doesn't do it, best to start from the beginning. That included the stem o-ring and while it's removed, run a piece of Scotts Brite in the o-ring groove to make sure there aren't any left over bits of degraded o-ring material left in there. BTW, just because you have a NOS piston, does not necessarily mean the end is not dinged.

 

[buddhasummer]

Guru said, "Is it leaking from the ambient ports?"

Try putting electrical tape over the ambient chamber holes and let the first stage sit pressurized for a few hours. If there is a leak in the ambient chamber, a bubble will form in the tape.

I've found that the most likely cause of erratic IP is a problem with the seat. Perhaps dirt or a scratch or miss matched engraving. The easiest thing to try is a new seat; if that doesn't do it, best to start from the beginning. That included the stem o-ring and while it's removed, run a piece of Scotts Brite in the o-ring groove to make sure there aren't any left over bits of degraded o-ring material left in there. BTW, just because you have a NOS piston, does not necessarily mean the end is not dinged.

Thanks Couv, I will check for a leak as you suggest. Take a closer look at the piston and replace seat. The Piston, I believe, is new new stock as opposed to NOS. After checking for a leak and changing seat if no joy, I'll tear it down and start again. I'll post back with results.

 

[buddhasummer]

Changed seat, same issue. Guess I'll be tearing it down this weekend and starting again, all the fun of the fair.

 

[rhwestfall]

sorry I didn't respond, but I've not directed much attention to my MK-10/10+ stages in the recent past. I honestly don't recall if my issue was resolved, or it it persists and I abandoned it.... too many projects going on....

I do most of my "fun" diving with my DH regs, and my "tech" stuff is on my MK-17's or my Poseidon stages.

hoping to invest time in them soon again...

watching this thread for beneficial information.

 

[redacted]

If not the seat, then it must be the piston. A small defect in the sealing edge might cause that problem. It should be visible with enough magnification.

 

[buddhasummer]

Cheers Bob, will keep this thread updated.

As much as I like "playing" must say that I've found diaphragm regs seem to go together easier, never had an issue with any of them. Not entirely sure what it means but every used diaphragm reg, regardless of age, I've ever bought has worked upon arrival in contrast to almost every piston reg I've bought which has not. Having said that probably not in large enough numbers for any statistical accuracy/analysis.

 

[buddhasummer]

If not the seat, then it must be the piston. A small defect in the sealing edge might cause that problem. It should be visible with enough magnification.

I have a loupe, I'll check it closely when I remove it. Cheers.

 

[buddhasummer]

Update: took a jewelers loupe to the piston, looked "ok", nothing stood out. Used some 3200 micromesh and Brasso. Reassembled, starts at around 142psi and over a few mins creeps to just shy of 150psi and seems to be holding. So looks like a creep of about 8psi.

Next question, I'm using no shims on seat carrier, I've assembled hp side as per schematic with the spring centering washer and above that a washer/shim.

To reduce the ip I'm going to need to remove something. I'm guessing if I remove the washer and leave the spring centering washer in place it'll drop around 5psi?

Given many MK10s, even though latest schematic shows both MK10 and Plus using spring centering washer, do not use this centering washer can I remove it?

Am wondering what to remove internally as I can make up ip if I need to using seat carrier shims.

Any advice is appreciated. Cheers.