MK 10 DIY - to Duro or not to Duro, that is the Question!

[Hawaii Treasure Finder]

Have always enjoyed reading the DIY how-to's on the forum as I'm an avid tinkerer.

I would be interested to get feedback on something I'm currently working on now.

I've been servicing my own MK10 for a few years - and I find the 'appropriate' o-ring by comparing the old ones I've taken out to my new o-ring collection (I've got 70, 75 & 90 duro of every size o-ring), and then figure out the duro based on the 'squeeze test'...

Now that it's been a few generations of servicing my regs in this manner, (and realising that over time one mistake leads to many down the line), I saw COUV's reply to a poster regarding how-to lower IP using a higher duro on the piston shaft o-ring - So... was just considering - I'm guessing it's not such a big deal to get the duro wrong (if switching o-ring duro for such an important o-ring is 'flexible') OR are there certain o-rings in the MK10 line-up that MUST be a d75 or a d90...? IF so, which ones?!
Thanks in advance for the feedback!

 

[Couv]

The piston stem o-ring MUST be higher duro (85-90) or extrusion is very likely. I don't remember the thread you're referencing, but I should have explained it better than just saying harder equals lower IP. The mechanics involved are a bit different. If a lower duro o-ring is installed in that position and extrudes, it will slow the piston action down and cause the IP to rise. In fact, anything that slows the piston's action will increase the IP. That could be a less effective lubricant, stiffer spring, shorter seat, body or seat cap not torqued all the way, etc.

@halocline has had positive results (meaning lower IP) using polyurethane o-rings installed in the piston stem groove. I tend not to buy PU as the shelf life is only 5 years. I'm cheap and don't like to inventory my stock. Indeed, some of the PU o-rings I've had turned to crispy critters before I had a chance to use them.

Re most of the other o-rings on a MK10-duro: Keep in mind where there is a high pressure differential a high duro o-ring should be installed such as the HP ports; but it's not as critical as the piston stem.

@Zung took my annotated MK10 schematic and improved it greatly by listing the SP recommended o-ring durometer and material, but I'll be darned if I can find it right now.

 

[rhwestfall]

Zung took my annotated MK10 schematic and improved it greatly by listing the SP recommended o-ring durometer and material, but I'll be darned if I can find it right now.

subscribing in hope it shows up..

 

[Hawaii Treasure Finder]

The piston stem o-ring MUST be higher duro (85-90) or extrusion is very likely. I don't remember the thread you're referencing, but I should have explained it better than just saying harder equals lower IP. The mechanics involved are a bit different. If a lower duro o-ring is installed in that position and extrudes, it will slow the piston action down and cause the IP to rise. In fact, anything that slows the piston's action will increase the IP. That could be a less effective lubricant, stiffer spring, shorter seat, body or seat cap not torqued all the way, etc.

@halocline has had positive results (meaning lower IP) using polyurethane o-rings installed in the piston stem groove. I tend not to buy PU as the shelf life is only 5 years. I'm cheap and don't like to inventory my stock. Indeed, some of the PU o-rings I've had turned to crispy critters before I had a chance to use them.

Re most of the other o-rings on a MK10-duro: Keep in mind where there is a high pressure differential a high duro o-ring should be installed such as the HP ports; but it's not as critical as the piston stem.

@Zung took my annotated MK10 schematic and improved it greatly by listing the SP recommended o-ring durometer and material, but I'll be darned if I can find it right now.

Thanks so much Couv for the reply - yes, I should have copied the link I was referencing to avoid confusion/extra work looking for it!
This was an informative reply and from memory, I just did install the piston stem o-ring as a 90 duro viton, but think the large o-ring around the head of the piston (size 17?) was a viton duro 75... I can easily change that to a 90 if need-be.
To date I have not had a failure and I'm working hard never to have one! I dove about 1 year on the current service but opening the reg I found it full of very fine grit and sand - all the way thru the reg - low pressure chamber to high. We do a lot of shore diving here and I often dive in/thru sandy surf. I was actually surprised that the grit in the reg hadn't cause a problem.
Thanks again for taking the time to reply. Appreciate your feedback!

 

[Couv]

but think the large o-ring around the head of the piston (size 17?

-017

duro 75

Duro 75 is fine for the piston head as it does not see a high pressure differential.

 

[Hawaii Treasure Finder]

Awesome, thanks much!

 

[rsingler]

Thanks so much Couv for the reply -
...opening the reg I found it full of very fine grit and sand - all the way thru the reg - low pressure chamber to high. We do a lot of shore diving here and I often dive in/thru sandy surf. I was actually surprised that the grit in the reg hadn't cause a problem.

And that's why a DIY SPEC Boot is just what you need for your home-brew Mk10!

 

[ams511]

@Zung took my annotated MK10 schematic and improved it greatly by listing the SP recommended o-ring durometer and material, but I'll be darned if I can find it right now.

Is this the thread your looking for? Scubapro O-ring Sizes

 

[Couv]

Is this the thread your looking for? Scubapro O-ring Sizes

Perhaps, but I could not find the file in there.

 

[ams511]

Perhaps, but I could not find the file in there.

It is not on the VDH site?