MK5 HP Seat

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Art Challacombe

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Location
Hawaii
# of dives
I just don't log dives
Aloha everyone,
recently I purchased a nice looking MK5 first stage on an auction site. Upon receiving it, I checked the IP and it had a creep up to around 148 psi. Feeling it was too high, I proceeded to tear it down for a rebuild. To my surprise, the white HP seat face was flat as opposed to the normal concave configuration. So, I replaced it with a Scubapro -1 seat, rechecked the IP and after recycling the IP had a final lock up at 128 psi which is fine with me.

I’ve never seen a flat HP seat in a MK5, so my question is; is this seat correct for Scubapro regulators? Other than not having the concave face, it fits the HP carrier perfectly and looks new. There is no number or markings on the seat. Any ideas?
 
Lots of flat inexpensive aftermarket seats around. They match the original flat Mk5 seat, which was discontinued after the cone seats were introduced.
But your flat seat isn't "wrong". Another possible cause of your IP creep is an imperfection in the knife edge. The cone seats are more forgiving of that.
 
Thanks rsingler, that makes sense to me. Fortunately, the previous IP creep was not from the piston. I checked the knife edge with a jewelers loop and the edge is perfect. Also, I left the the regulator on a full tank overnight. It read 125 psi last night and today it’s at 128. I’m satisfied with those numbers.
 
I’m guessing that perhaps the seat face had not had not been cycled enough to create a permanent lock. To be fair, the initial IP was at 138 and creeped up to 148 after a couple of hours. Maybe I should have been more patient and cycled the regulator as Pete Wolfinger says.
 
Reviving this thread for a similar question.

I have a MK5 and a MK9 that are locking up at IP of 155 and 160. There aren't any shims in the MK5. Not sure about the MK9 but it's full of silicone so I'm not in the mood to take it apart right now. Do the seats from VDH correspond to a Scubapro (+)? I assume I need a (-II)?
 
Reviving this thread for a similar question.

I have a MK5 and a MK9 that are locking up at IP of 155 and 160. There aren't any shims in the MK5. Not sure about the MK9 but it's full of silicone so I'm not in the mood to take it apart right now. Do the seats from VDH correspond to a Scubapro (+)? I assume I need a (-II)?
Yes, they are made to the same specs, as are the O-rings. I've used their MK5 1st stage and the 109 to 156 conversion kits for balanced 2nd stage. The MK5 kits includes a few different main seats.
The performance is flawless. The last rebuild I did lasted for 4 years and may have gone longer but 4 years was my limit.
 
Thanks AfterDark. My service kit only came with the one seat though, and I'm not sure which one it is.
 
Thanks AfterDark. My service kit only came with the one seat though, and I'm not sure which one it is.
The seats I use are white and concaved on one side.
 
I think it's just time for me to do a complete service on the MK9. I'll order the new kit with the new seat.
 
The nice thing about the old white flat seats is that at service time you can simply reuse them flipping the side which seals against the piston. I have yet a pair of them...
Of course I also have many new conical seats (the service kit containing them was designed for rebuilding either a MK5 or a MK10). Each kit contains three conical seats, each of different height, so they lock at different values of IP.
 
https://www.shearwater.com/products/teric/

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