MK 25 service of seat o-rings.

[triggerman365]

I posted my issue, here with my Mk 25 in the regulator section, but thought it is better to post my latest question here. Here goes.

Can the MK25 HP seat be remove and inspected and o-rings inspected/replaced, without removing the yoke assembly and/or disassembly and further? I am of course hoping it would be as simple as a bad o-ring. Thanks for the help.

 

[Zung]

Yes you can, with care.

1. Mount the reg on a tank with some air in it, air off
2. Remove the seat retainer, put the loose parts in a safe place
3. Cover the opening left by the retainer with a rag, or your thumb, but it may hurt
4. Turn on the air, very slowly
5. The seat and its parts (2 rings, 1 o-ring, 1 spring) will blow out
6. You may need to poke at the HP o-ring; use only biodegradable wooden toothpick

I would replace the HP o-ring no matter what: you need a 2-010 Duro 90 in Viton, PU, or EDPM. Inspect the other around the seat: it's a 0-011, same specs.

Lube the o-rings and assemble in a logical order: using the numbering of schematic 10-710-X00 (06-2004): #23 - 22 - 21 - 20 - 18. The 2 rings (#23 & 21) have a specific orientation: 21: blind holes toward the piston crown; 23: shoulder toward the seat retainer.

Initially, the IP may drift a bit because you disturbed the seat; it may improve after cycling a few times.

 

[halocline]

I personally would not start by taking the HP piston o-ring and bushings out. Just take out the retainer, you don't need any air, leave the HP piston o-ring and bushings in place. The spring will likely fall out. Then replace the o-ring around the seat (011, EPDM, duro 85 or 90) and the washer that sits on the seat retainer flange. I'd be willing to bet that the problem is that the o-ring around the seat is not seated correctly or defective. If the o-ring looks fine (I use a jeweler's loupe to inspect them for tiny nicks) you can re-use it, just lube it well with PTFE grease and make sure it's seated correctly.

Once you take the piston o-ring and the bushings out, it's really best to take the piston out, use the SP tool to re-seat bushings and o-ring, and then put the piston back in. IOW, more-or-less a new rebuild. So first, see if the seat retainer o-ring does the job. When the guy "tightened" the seat retainer, it stopped the squeal for a while, so that's probably the issue. If not, then you can try Zung's approach, but honestly I don't think you'll have much luck getting the bushings and HP o-ring over the piston edge like that. Maybe I'm wrong!

I am not very familiar with the MK25 external IP adjustment, not owning one. But if there's an o-ring around that little set screw that pushes the plate that moves the seat, that might be another spot. There's no o-ring on the schematic that I have, but I have heard about leaks around that set screw. I like the MK20 arrangement that forgoes the 'convenience' of external IP adjustment and does not present any extra leak points in the HP section. Eventually if you get cranky like me, you could find a MK20 seat retainer and downgrade.

 

[redacted]

Which o-rings need to be removed and inspected depends on where the leak is located. If you are trying to fix the problem without first identifying the problem, it is unlikely you will have any joy. A bad seat on the HP piston o-ring will bubble out of the ambient chamber. a bad seal on the HP seat o-ring will bubble from the seat retainer. A bad seal on the yoke or din retainer o-ring will bubble from around that retainer.

---------- Post added April 15th, 2013 at 09:15 AM ----------

I am not very familiar with the MK25 external IP adjustment, not owning one. But if there's an o-ring around that little set screw that pushes the plate that moves the seat, that might be another spot. There's no o-ring on the schematic that I have, but I have heard about leaks around that set screw. I like the MK20 arrangement that forgoes the 'convenience' of external IP adjustment and does not present any extra leak points in the HP section. Eventually if you get cranky like me, you could find a MK20 seat retainer and downgrade.

I can't find the TSB that addresses that but I'm fairly sure the added o-rings are just sealing out water and do not provide a breathing gas seal. the breathing gas seal is provide by the o-ring on the HP seat.

 

[halocline]

Which o-rings need to be removed and inspected depends on where the leak is located. If you are trying to fix the problem without first identifying the problem, it is unlikely you will have any joy. A bad seat on the HP piston o-ring will bubble out of the ambient chamber. a bad seal on the HP seat o-ring will bubble from the seat retainer. A bad seal on the yoke or din retainer o-ring will bubble from around that retainer.

That's all true, but this guy has an intermittent leak; it's apparently stopped squealing so he might not be able to immediately identify the location. So he could wait until it happens again and then try to find the leak, or replace everything, or start replacing the easiest and most likely culprit. It might be worth getting out the HP tank again and try to make it squeal, then submerge and look for bubbles.

 

[Zung]

... Once you take the piston o-ring and the bushings out, it's really best to take the piston out, use the SP tool to re-seat bushings and o-ring, and then put the piston back in. IOW, more-or-less a new rebuild. So first, see if the seat retainer o-ring does the job. When the guy "tightened" the seat retainer, it stopped the squeal for a while, so that's probably the issue. If not, then you can try Zung's approach, but honestly I don't think you'll have much luck getting the bushings and HP o-ring over the piston edge like that. Maybe I'm wrong!...

If I may respectfully disagree regarding the installation procedure.

In the EB267 dated Feb 14, 2000, SP introduced the composite piston, along with a revised installation procedure. Here it is, verbatim:

Install the piston assembly into the regulator body (swivel cap side). Be certain that the piston head is pushed firmly into the body.
Be certain to lubricate the piston head o'rings to dynamic specifications

Install the Ultra-Glide Bushing on the MK 20 Assembly Tool. Note that the "blind" holes on the bushing face outward.
DO NOT INSTALL THE STEM O'RING, OR THE SHOULDERED BUSHING AT THIS TIME

Using the MK 20 Assembly Tool, carefully insert the Ultra-Glide Bushing into the regulator body.
Note: The stem o'ring and shouldered bushing are NOT to be installed at this time.

Keeping the MK 20 Assembly Tool in place, carefully thread the swivel port and regulator body together. Tighten by hand while holding the MK 20 Assembly Tool.

Install the stem o'ring carefully over the seating edge of the piston stem. Once it is in place, install the shouldered bushing over the piston stem.

Using the MK 20 Assembly Tool, check to see that the Ultra-Glide Bushing System is correctly installed. Tighten using the Field Handle. If the bushing system shifts during the final tightening process, use the MK 20 Assembly Tool to push it securely down.​

I think they do this to avoid any damage the sharper edge of the composite piston may cause to the o-ring.

... I can't find the TSB that addresses that but I'm fairly sure the added o-rings are just sealing out water and do not provide a breathing gas seal. the breathing gas seal is provide by the o-ring on the HP seat.

That's EB274:

This modification is meant to address the remote possibility of water drops entering through the threads between the seat retainer and the adjustment screw and thus, in the case of the MK25UL only, to form some oxidation (figure 1). For consistency, the change is extended to the entire line. With the new parts, o-ring (O) and washer (W) (fig. 2), the area in question is sealed and dry.​

It doesn't do anything to a normal brass MK25.

 

[ams511]

1. Cover the opening left by the retainer with a rag, or your thumb, but it may hurt

When I blow out a part I put a ziplock bag over the opening (close the rest of the bag) and catch the part in the bag. I have only tried this using BC hose air gun and it works well. If using high pressure air you may want to put a few small holes in the bag so it does not inflate and blow out of your had.

 

[redacted]

I use a tank with an air gun through an LP port. With 130 psi, things don't go very far and a catch in the hand is painless.

 

[halocline]

In the EB267 dated Feb 14, 2000, SP introduced the composite piston, along with a revised installation procedure. Here it is, verbatim: (etc....)

​

​

It's nice to be wrong from time to time, but don't you use the installation tool or a bullet to push the o-ring over the piston edge? If not, how do you do it? You have to use something and you have to be very careful about damaging the piston edge with a tool.

Anyhow, I still think this guy's problem is not in the HP piston o-ring, but maybe I'll be wrong about that too!

 

[Zung]

As always, I use a toothpick as a preferred universal scuba tool.
The o-ring (and the bushings) go into a cylindrical space between the stem and the wall, there's no way they could misbehave or not do what they're told.

I have the genuine assembly tool, but it's a write off, as you can easily skip paragraph 3 of the recommended procedure and install both bushings and the o-ring at the same time. Last time I did the wife's MK25, I even forgot I have the tool.