Mk10 piston oring removal

[aquaregia]

I can't get the piston oring out of my Mk10. I'm used to having trouble getting it in, but usually it pops straight out with the piston. Any suggestions?

 

[redacted]

I use a double hook pick from scubatools. I use a stone to dull the point. I slip the hook down one side of the o-ring and rotate the pick so the point hooks across the o-ring.

Another option is to work from the ambient chamber side to stab the o-ring with a straight, sharp pick. This will scratch the surface of the gland but that inner surface seal does not contribute to holding gas pressure.

 

[aquaregia]

Thanks, went and hunted picks until one worked.

I had something odd happen though -- I used the same shims (2) and seat ("+") as I have the past few times I've done this, and the IP is stable but real high (160). Isn't the "+" marked seat the lowest IP one? If I open the body up again to remove the shims is the seat toast from taking a set already? I'm not seeing or hearing any blowoff from the 2nds, so I'm pretty sure the IP isn't just rising indefinitely.

 

[redacted]

The + is the highest IP. The -l lowers it one step and the -ll lowers it another step. I think each step is about 5 psi. You can remove the seat carrier but do not disturb the seat if you want to reuse it. Even removing the 2 shims may only bring it down 8 to 10 psi. If there are other thin plastic bits on either end of the piston (like on a Mk-10 Plus) you might also want to remove them. That may let you get that + seat down into the 130 - 140 range. If you remove all the plastic bits from the ends of the spring and IP is still to high, I have added a Mk5 shim (01.060.219) or two between the seat retainer and the body to raise IP without removing the piston. But you have to watch that they do not interfere with the O-ring seal between the retainer and the body. If it leaks, loosen and retighten it to get it to seal. Once it seals it will be OK.

I hate to waste a perfectly good seat. It's not like you can walk into any shop and buy one.

Good luck.

 

[aquaregia]

Right on the money with your estimate -- no shims 150psi. Still too high? I don't have any Mk5 shims handy, so looks like my options are to ride with it or stick in the -II. Leaning towards the -II...

 

[rhwestfall]

IIRC 150 is the top end of the acceptable range. I'd never dive it there as we are in cold water (<45F), but it might work for you..

 

[redacted]

I screwed up in post #4. Adding shims between the seat retainer and the body raises IP rather than reduces it. But, that does lead to another alternative. I have cut HP seat diameter disks from nylon sheets the thickness of shims and added them between the HP seat and the retainer to reduce IP. You will need to mark the position of the seat in the retainer so it can be reinstalled in the correct orientation. Warning: you should have no problem adding 1 or 2 to drop IP about 10 psi but don't go further than that. I tried lowering IP low enough to power air tools. Somewhere around 90 psi the piston locked up in the seat and would not pull free even when I dumped the intermediate pressure to ambient. Oops.

 

[aquaregia]

-II took it to 137. Just a note for future self...

 

[rhwestfall]

-II took it to 137. Just a note for future self...

bulls-eye!

 

[rhwestfall]

caution, a couple cycles can lead to less IP as the seat takes a set...