MK 25 service of seat o-rings.

[triggerman365]

I was finally able to get my mk25 on a tank with sufficient pressure to recreate the squeal. I then submerged the regulator while on the tank and the bubbles are leaking out the ambient chamber. So, as awap pointed out it appears to be the o-ring on the hp seat. Any other possibilities? One thing I should mention, after the second time I took it in to the tech, he said he replaced an o-ring that was bad, but didn't say which one. Could there be some issue that is causing the hp seat o-rings to be damaged, since this may be the second one since the original bad service job?

 

[redacted]

I was finally able to get my mk25 on a tank with sufficient pressure to recreate the squeal. I then submerged the regulator while on the tank and the bubbles are leaking out the ambient chamber. So, as awap pointed out it appears to be the o-ring on the hp seat. Any other possibilities? One thing I should mention, after the second time I took it in to the tech, he said he replaced an o-ring that was bad, but didn't say which one. Could there be some issue that is causing the hp seat o-rings to be damaged, since this may be the second one since the original bad service job?

A leak from the ambient chamber has a few other possibilities but the tank pressure dependence points quite strongly to the HP seal so probably the o-ring but a metal sealing surface or a plastic bushing could be the culprit. I'd remove the O-ring and inspect it hoping to find a defect and know that is the culprit. Defect of not, replace it and hope that does the job.

One nice thing is such a leak is not likely to get much worse very quickly. So you should be able to dive the regulator with confidence and cuss a little if the leak re-appears.

BTW ambient chamber leaks can also be caused by problems on the IP side with the piston head o-ring and its sealing surfaces or even the internal o-ring in the composite piston. (I have replaced one but Scubapro does not endorse the repair or even acknowledge the existence of that o-ring.)

 

[halocline]

I was finally able to get my mk25 on a tank with sufficient pressure to recreate the squeal. I then submerged the regulator while on the tank and the bubbles are leaking out the ambient chamber. So, as awap pointed out it appears to be the o-ring on the hp seat. Any other possibilities? One thing I should mention, after the second time I took it in to the tech, he said he replaced an o-ring that was bad, but didn't say which one. Could there be some issue that is causing the hp seat o-rings to be damaged, since this may be the second one since the original bad service job?

I guess it's possible that the tech scratched something in the process of removing the old o-ring and bushings, but the bushing system in the MK25 is supposed to help prevent that. In the older SP piston regs, the HP o-ring simply sat in a groove in the regulator body, and sometimes careless techs would scratch the seating surface while removing the old o-ring. This would be the end of the regulator. Then SP came up with the plastic bushing arrangement to make removal of the old o-ring much easier and to improve tolerances around the piston/o-ring seal.

Just to be clear, the bubbles from the ambient chamber indicate the problem is with the HP o-ring on the piston shaft, not the one around the seat, which is the one I thought would be the culprit. Wrong again...hehe

Anyhow, at this point you could go back to the shop and ask them to start over with a new kit, or you could follow Zung's procedure for removing the spring, 2 bushings, and o-ring from the piston shaft. Then you'd make sure there are no nicks in the bushings (jeweler's loupe) and find a new HP o-ring. You need a size 010 duro 85 or 90, viton or EPDM o-ring. You also need some lubricant; PTFE grease like tribolube or Cristolube is the typical lube.

 

[Zung]

Can you find that o-ring locally? I seem to recall sometimes you find 2 such o-rings in the official kit; they're marked with a red stripe to indicate they're the harder variety. Worse case, a nitrile (NBR) will do if you go easy with O2 level.

If you remove the original o-ring, post a pic; I'd like to see the shape it's in.

 

[triggerman365]

Just to be clear, the bubbles from the ambient chamber indicate the problem is with the HP o-ring on the piston shaft, not the one around the seat, which is the one I thought would be the culprit. Wrong again...hehe

So, from what I understand, it should be part #22, 01050136, is that correct?

Can you find that o-ring locally? I seem to recall sometimes you find 2 such o-rings in the official kit; they're marked with a red stripe to indicate they're the harder variety. Worse case, a nitrile (NBR) will do if you go easy with O2 level.

I can get it/them locally.

If you remove the original o-ring, post a pic; I'd like to see the shape it's in.

I will, but won't get around to working on it until this weekend.

 

[halocline]

So, from what I understand, it should be part #22, 01050136, is that correct?

I can get it/them locally.

Yes, that's the one, but I would also replace part #19 (138) which is a 011 (one size bigger) o-ring. The other one that sometimes causes HP leaks is the 'other' part #19 the o-ring on the end of the yoke retainer, but the one I'm referring to is the one on the seat itself.

 

[triggerman365]

Well, I tried using only LP to blow out the HP ring (#21 with o-ring #22 from the above schematic) and they did not come out. Should I go for the HP to get it out?

By the way, the O-ring on the seat looks perfect.

 

[redacted]

Well, I tried using only LP to blow out the HP ring (#21 with o-ring #22 from the above schematic) and they did not come out. Should I go for the HP to get it out?

By the way, the O-ring on the seat looks perfect.

That bushing and o-ring will not blow out - that only works on the seat. You might be able to tap them out after the seat and string are removed. I usually remove them with a pick after I remove the piston. But then you really want an assembly tool to reassemble.

 

[Zung]

Or remove the cap, the piston, and poke with a wooden chopstick from the cap side.
You'll need a hook spanner to remove the cap.

 

[triggerman365]

Well, my MK 25 is still messed up, but on the bright side. I rebuilt a SP 109, replacing all the parts with brand new and went diving with it today. It worked perfectly. I really like these 109's!