Question O-Rings Vs Quad Rings for Piston Seal on MK10 Clone
- Thread starter JP_SCUBA
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I think you both meant 90 Duro for the 2-010 HP ring, yes? 70 for the piston head; 90 for the shaft.
At least, that's what's on its way.
At least, that's what's on its way.
JP_Scuba mentioned trying a 70 Duro for the -010 HP ring back on post #20.
So I figure if a 70 duro holds up for a test it will bode well for the proper 90 duro ring that you are sourcing for us.
In my beginning days of diy, not really knowing better, I installed a 75 duro -010 piston oring and dove it for a while with no problems.
But now thinking of diving a first stage with 70-75 duro orings in high pressure areas makes me shudder a little...
halocline
Contributor
I believe SP went to an odd duro like 85 from 90, don’t recall if I heard why, better seal, stop the squeal that MK 10 brought with it or just to be different but I’m looking forward to hearing how the 70 does in this application, the quad may prove something one way or the other.
OK, with the piston shaft -010 o-ring replaced with a 70 duro -010 quad/X-ring, I set IP at 135 with just under 2500 psi tank pressure and it held at that all night. No creep or leakage. Took several breaths with it both slow and rapid for several minutes while watching IP fluctuation and it always returned to 135 psi and delivery was good. I let it sit for 3 more hours while under pressure and all was stable. I guess we hit the pool next... Now this is all fine in my "controlled environment" and my pool is a salt chlorinated pool, but it doesn't have anywhere near the salt concentrations of the ocean so actual ocean dives will have to be next. I'll have to see when I can do that. ......
halocline
Contributor
Are you talking about a MK10? If so, please measure the IP at 500PSI, then 1000, then 1500, 2K, 2500, 3K, if you can. It's not hard if you have a full tank. You just turn the tank valve off (measuring 3K first) and then bump the purge to bring the supply pressure down to whatever you want. My guess is that with a 70 duro ring in there, you'll find that there is significantly higher IP at 3K than say, below 1K.
halocline
Contributor
Yes. A softer o-ring will cause more friction in the piston movement at higher tank pressures.
MK10s generally have more rise in IP at high tank pressures than do other SP balanced piston 1st stages. I'm sure this is due to the smaller piston head. Basically, there is less total force on the piston head, with the same friction issues of the MK5 at the HP piston o-ring spot, so friction increase is a higher percentage of total force. The more that o-ring extrudes or gets moved around, the more friction there is and that increases the force required to push the piston against the seat. Higher duro o-rings are supposed to extrude less. You may already know this stuff, if so please excuse my verbosity.
The best performing HP o-rings I've used are 90 duro polyurethane o-rings. But they have a different set of problems, primarily shorter shelf life. I got a batch of bad ones once and I just stopped using them, now I use EPDM or viton.
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