My MK2 is an MK3

[parzdiver]

I have been working on a few older regulators I got off e-bay. Two are MK5's and I thought an older model MK2 SPEC. It turns out after looking more closely and ordering o-rings, my MK2 is actually a MK3. The larger piston is much smaller than the piston from the MK5 and based on the scematics, the MK2 & MK5 have about the same size piston.

So, assuming the same HP seat can be used, does anyone have the o-ring sizes for the MK3? Of course I just ordered some assuming it was an MK2, so hopefully the small piston o-ring will be the same (-008). But the large piston o-ring definitely will not be. I'll have to get a different o-ring.

Thanks!

 

[parzdiver]

Of course, just after posting, I found the schematic for the MK3, my answer is Scubapro Part Number 01-050-168, which translates to -019, according to the Scubapro O-ring Size thread here on ScubaBoard....

And the small piston o-ring is the same as on the MK2.

 

[Zung]

That's DIY taken to the next level: AIY: Answer It Yourself.
Way cool

 

[parzdiver]

Thanks Zung

So, besides the piston being different, is there much functional or performance difference between the MK3 & MK2? Will this be perfectly fine as a stage reg?

 

[Texfrazer]

The Mk3 will work incredibly well as a stage reg.

 

[parzdiver]

So - I got all of my o-rings and seats and what not. I put everything together. I tried each stage with a known working stage from my OMS Workhorse. The 108 seems to work very well. I haven't measured cracking pressure, but objectively it didn't breath bad. I'll do the bucket test or put together a manometer to check.

The MK3 first stage isn't bad either, with one big exception. My IP was a solid 135. Quick recovery without a big drop when breathing. However, I wasn't able to let it sit to see if it would creep.

The Problem - there is a leak where the HP hose connects to the first stage. I tightened, still a leak. I replaced the o-ring, still a leak, I took the HP hose and gauge from the Workhorse which doesn't leak, and there is (altogether now) still a leak. I don't have a good magnifier, but to the mark-1 eyeball it looks okay. I ran my fingernail over the sealing surface and it also seems okay, nothing caught.

Besides something being "off" on the sealing surface, does anyone have any other ideas?

Thanks in advance!

 

[redacted]

I think you need to give that sealing surface a real close inspection. Remember, it seals inside the port opening. You might also try a port plug rather than a hose as they use different size o-rings and may seal differently. I have had some luck buffing out scratches on ambient chamber sealing surfaces for LP piston o-rings so, even if you find damage or a defect, there may be hope.

 

[parzdiver]

I think you need to give that sealing surface a real close inspection. Remember, it seals inside the port opening. You might also try a port plug rather than a hose as they use different size o-rings and may seal differently. I have had some luck buffing out scratches on ambient chamber sealing surfaces for LP piston o-rings so, even if you find damage or a defect, there may be hope.

I think I made an assumption and it didn't help me in this case. According to the MK3 schematic, the HP plug uses a 01-050-138, which seems to translate as a -011 thanks to the hard work of the many SB DIYers. That is what I tried on the hose assuming they'd use the same o-ring. After seeing your post, I gave a -012 a try. IT HELD! At least for about 10 minutes at about 2300 PSI. Then I had to come to work, so I shut the tank valve and drained system to the 50 bar mark. Even if the o-ring extrudes, it shouldn't cause much of a problem. I'll see how the system holds when I get home.

Did I make the right choice of o-ring for this? Or is it just a matter of time until extrusion?

 

[parzdiver]

Here I go again with the AIY - Answer It Yourself. It appears that in most references, the -011 is used on LP hoses and the -012 is used on HP hoses. -010 is used on the second stage side of the LP hose.

Please correct me if I'm answering myself wrong.

Did I make the right choice of o-ring for this? Or is it just a matter of time until extrusion?

 

[redacted]

Yes, I believe you have it correct.