Scubapro MK10 issue. Bad seat or something else?

[tom-153]

Cross-posting from the equipment section; thinking perhaps this is the more appropriate place for this question?


Hi guys,

I recently picked up a used MK10/g250/g200 setup and just hooked it up to a tank to test it out. Low and behold, the 1st stage appears to be leaking air internally and the IP spikes up to 180+psi. I can feel the air coming out of the small holes around the 1st stage and the top part (where the low pressure hoses connect) is clearly getting cold and you can see condensation forming there.

Here's a video; I turn down the air just to prevent the octo from free flowing from excess pressure:


Any ideas what the issue may be? I believe I read that bad o-rings would cause this kind of an air leak and that something like this can be caused by a bad HP seat or a piston. Hoping it's just a piston and a simple service will get it back in shape.



Would love to hear people's thoughts.
Thanks!

 

[rjack321]

seat failure combined with piston oring failure

Likely caused by water getting inside (wet fill, rinsed uncapped, or depressurized underwater) leading to internal corrosion on the seat surface and main body. Needs parts but also needs major internal cleaning/descaling - hopefully the seat sealing surface isn't completely ruined.

 

[rhwestfall]

possibilities:

piston o-ring, piston stem o-ring, seat, ambient chamber body corrosion......

commence rebuild

 

[herman]

If air is coming out the ambient chamber holes one or both piston orings are defective. This would also cause the excess pressure. Unless one of the oring sealing surfaces is damaged, it's an easy fix with a service kit.

 

[uncfnp]

Here ya go...

Store | Vintage Double Hose

And make sure you get Herman’s Piston o-ring tool too.

 

[tom-153]

Thank you all! Hope it will be a simple fix.

Herman, I've already reached out to you earlier about some parts, but I wanted to put this thing on a tank first. Will be in touch shortly.

 

[tom-153]

Well, well, well. You guys were right!
Just look at that seat. The main piston o ring is totally flat too and the one that sits inside the chamber is hard as hell to remove; I’ve been pulling it out in pieces. The piston edge feels nice and smooth. I think there may be a scratch or two on the shaft itself, but I really need to clean it up first to be sure. If there are some scratches/pitting, is it a huge deal, or is the edge the most important thing? If it is a big deal then can the defects be polished out?


Best regards.

 

[herman]

Pitting or scratches on the piston shaft may or may not be a problem, it depends on where they are at. Anywhere the stem oring rides can be a problem, above or below that, not a big deal....and I wouldn't mess with it other than a light pass with scotchbright. to remove any burs that may snag the oring as the piston is installed. The other place you need to check for corrosion is the area where the head oring seals. Scratches or pitting there is a problem, luckily it can usually be buffed out unless it's bad.

 

[tom-153]

Thanks Herman!

Some 1k-2k wet sand paper and metal polish? #0000 steel wool and metal polish? I’m assuming the finer finish on the surface the better in this application, since it’s sealing with rubber o-rings?

 

[tom-153]

Is this turret nut on a MK10 removed by simply chocking the reg at the LP port and removing it with an allen in the attached pic? I watched Bryan’s MK5 disassembly video, but this thing looks different.