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MK20 fresh rebuild - how much creep is normal?

Discussion in 'Regulators' started by snowdog61, Apr 25, 2017.

  1. snowdog61

    snowdog61 Solo Diver

    # of Dives: 500 - 999
    Location: Florida's East Coast
    870
    558
    Just finished rebuilding the GF's MK20 and after putting pressure to it, it locked up at 147 - figured I'd need to remove a shim at some point so started into seating it and began cycling the 2nd stage which dropped the IP to 115ish and returned to around 135 where it paused but then climbed back to 147. I attributed this to the seat and knife edge getting acquainted. After removing the thinner of the 2 nylon shims and cycling the 2nd stage probably 40 times the IP would pause at 125ish and creep over 5 seconds or so then hold at 137 consistently. Since it was consistent, I'm thinking it is OK but I'm not getting the reason for that creep. This is my 1st piston type reg so not sure what to expect - maybe the parts were just breaking in? My other rebuilds were all diaphragms and they have all locked up solid with little to no creep. Piston knife edge looked smoothed and polished under magnification.
     
  2. guruboy

    guruboy Divemaster ScubaBoard Supporter

    5,077
    810
    It's not unusual. Sometimes the Mk20's will creep. You can find a lot of information in older threads.

    Which kind of piston is in it?
     
  3. snowdog61

    snowdog61 Solo Diver

    # of Dives: 500 - 999
    Location: Florida's East Coast
    870
    558
    o-ring carrier portion is plastic (nylon?). Tube is stainless. So composite?
     
  4. Tbar

    Tbar Contributor

    # of Dives: 200 - 499
    Location: Australia
    612
    117
    My MK25 first stages lock-up with no creep when serviced. I wouldn't want creep over 5 PSI.

    The newer composite piston is not designed to 'cut' into the seat, but rather set on the seat's 'tapered' edge.
     
  5. Tbar

    Tbar Contributor

    # of Dives: 200 - 499
    Location: Australia
    612
    117
  6. guruboy

    guruboy Divemaster ScubaBoard Supporter

    5,077
    810
    the composite piston isn't supposed to creep.

    you can try letting it sit overnight or something to try and break in the seat.
     
  7. DIY

    DIY Divemaster

    # of Dives: 500 - 999
    Location: Ft Myers, Florida, United States
    175
    43
    I had one do this. Left it pressurized overnight and it was solid the next day. Not sure if this was the fix but worth a try.
     
  8. Tbar

    Tbar Contributor

    # of Dives: 200 - 499
    Location: Australia
    612
    117
    What was the IP situation before servicing? If it was creeping then, you likely have a piston issue, if it was solid an issue with servicing or the new seat.
     
    BoltSnap likes this.
  9. snowdog61

    snowdog61 Solo Diver

    # of Dives: 500 - 999
    Location: Florida's East Coast
    870
    558
    IP was 135ish but wouldn't lock up or at least I didn't didn't let it sit long enough deadheaded to see if it would. After a about 3-4 minutes it was over 145 and dribbling out of the 2nd. I probably could have cranked down on the adjuster to see how high it'd go but the end result would have been the same. It was slow enough however that I felt good with her diving on it but it was telling me that it needed a rebuild. We are diving this weekend so I'll check it when we get back. 2 hrs of use should get the parts broken in so if there's still an issue I'll dig back into it.

    Did look at the link - piston was upgraded at some point in its life since it is the newer composite type. I did put it under 10x to look at the orifice but guess I'll be looking harder if it is still creeping. Thinking the issue will be elsewhere though since it is locking up where it should - just taking a bit to get there.
     
    Last edited: Apr 26, 2017
  10. guruboy

    guruboy Divemaster ScubaBoard Supporter

    5,077
    810

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