Scubapro MK10 and HP Tanks

[tdmp]

This is the second time I've had to rebuild my MK10 in 5 months. It slowly bubbles from the ambient pressure holes in the main body, which (I believe?) indicates leaking from the main body o-ring that seals around the piston. The piston shaft is corrosion-free. My MK10 is usually trouble-free and I'm trying to figure out what the issue is.

I have been using the first stage lately with HP tanks usually 3600-3700 psi for a fresh tank. I am wondering, can the MK10 handle this pressure or could this be causing the issue? I had actually converted the 1st stage to a MK10 plus years ago but had a lot of issues with IP creep so changed it back.

Any input would be helpful.

 

[shurite7]

Have you looked at the o-ring that fits in the main body for wear on the edges? If there is, then the groove where the o-ring sits is wearing out.

You can also try to o-ring from the O2 kit. The green o-ring is made of a different material and may solve your issue.

 

[rsingler]

What @shurite7 said.
In one fashion or another, it's indeed your piston shaft o-ring. The tolerances in the Mk10 are sloppy enough that the orings deform at high pressure, and 3700 psi is well beyond their design spec.
You didn't say what you were using.
You might consider a 2-010 Viton duro 90 in lieu of the Scubapro 01-050-137 oring, or vice versa depending upon what you're using. A last alternative that should definitely handle the pressure is a polyurethane oring of 90 duro, though its lifetime is shorter.
A careful semi-polish of the piston shaft with no smoother than 6,000 grit Micromesh might also help, if things are sealing okay at the beginning, but shaft roughness is chewing up the seal. Smoother than that may actually increase friction, as @couv reminds us.

I'd buy one of those $15-40 Chinese USB microscopes and have a close look at the surfaces of your HP oring and piston shaft.

 

[tdmp]

What @shurite7 said.
In one fashion or another, it's indeed your piston shaft o-ring. The tolerances in the Mk10 are sloppy enough that the orings deform at high pressure, and 3700 psi is well beyond their design spec.
You didn't say what you were using.
You might consider a 2-010 Viton duro 90 in lieu of the Scubapro 01-050-137 oring, or vice versa depending upon what you're using. A last alternative that should definitely handle the pressure is a polyurethane oring of 90 duro, though its lifetime is shorter.
A careful semi-polish of the piston shaft with no smoother than 6,000 grit Micromesh might also help, if things are sealing okay at the beginning, but shaft roughness is chewing up the seal. Smoother than that may actually increase friction, as @couv reminds us.

I'd buy one of those $15-40 Chinese USB microscopes and have a close look at the surfaces of your HP oring and piston shaft.

Thanks, I've been using the standard SP kit. I'll try the polish option you mentioned and look for the 2-010 Viton duro 90.

 

[Scubagaskets]

Actually many scubapro o-rings with 010 size have different part number due to different material and hardness
Here is what we found to be correct
so 01.050.394= viton Sh90 orings Genuine Viton®O-rings 90 Sh-010-Premium O-rings Provider for Scuba
01.050.132=010 EPDM Sh70 Scuba O-Rings EPDM 70Sh-010 - Premium O-rings Provider for Scuba Diving
01.050.136=010 EPDM Sh85 Dive O'Rings EPDM 85Sh- 010 Premium O-rings Provider for Scuba Diving
01.050.137=010 POLYURATHANE Sh90 010

 

[Sunn]

sincerely impressed by your knowledge...

 

[happy-diver]

My Mk 10s, primary regs for years and years start their dives at 4206.09439ish Psi
and are rarely fully serviced

Aren't they magnificent!

 

[Sunn]

mine has been serviced 1 time in about 20 years... and last year they told me it was now impossible, as scubapro refuses to provide the original parts and prohibit the service by official dealers because this regulator can't reach the new european standards... sniff...

when I'll have time, I'll try to find everything to service it myself ! It was a beautiful companion.

 

[rsingler]

My Mk 10s, primary regs for years and years start their dives at 4206.09439ish Psi

Hey, @happy-diver, do you happen to know what HP piston shaft oring you or your shop uses? That's great to hear!

 

[Rusty Shackleford]

Standard service parts are available Sunn. New factory service kits were as of last year and may still be. Vintage Double Hose sells them.

The orings are all standard sizes and the seats are available from Trident distributors as well.