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georgeaustin
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Dynamic O rings / Back up rings (Singlehose)

Wed Jun 22, 2016 10:35 am

So - maybe I need to get a life but just to confirm an engineering question that's been keeping me up at night. I'm looking at dynamic o ring materials, sizes and use in piston regs specifically and I have a question for the guys smarter than me.
I suppose it's more about the back up rings than the actual o rings . .

Back Up Ring Purpose: To fill the extrusion gap but why do we never consider them for replacement when rebuilding piston type regs. Do you guys just confirm nominal / gauge fit and validate them based on visual inspection? ( no obvious signs of excessive wear or damage)

Also - do they have a dual purpose in limiting spiral damage to the dynamic o rings due to the very slow and very small amount of axial travel they see within the bore during operation.


Thanks

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Bryan
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Re: Dynamic O rings / Back up rings (Singlehose)

Wed Jun 22, 2016 2:28 pm

Luis would be the person to give details on the actual science behind this so I won't even bother adding my 2 cents.....I think he is on a dive trip so it may be a bit before he replies.

What Piston regulator uses a backup O-ring? Maybe I'm just confused by the terminology???? Do you mean a backup support ring as is found in the crown block on most balanced diaphragm first stages?
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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georgeaustin
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Re: Dynamic O rings / Back up rings (Singlehose)

Wed Jun 22, 2016 4:01 pm

No, just a nylon washer about .020 inch thick sitting under the single o ring in the piston head groove and under the O ring on the piston stem. Voit flow by piston model single hose

kworkman
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Re: Dynamic O rings / Back up rings (Singlehose)

Wed Jun 22, 2016 6:44 pm

I think backup rings are used to prevent extrusion. A thrust washer is a perfectly flat machined surface that I think serves the same purpose. I read a little on them when looking for parts to USD solid bar manifolds.

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antique diver
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Re: Dynamic O rings / Back up rings (Singlehose)

Wed Jun 22, 2016 7:43 pm

Some piston regulators started out with teflon backup rings being used with the orings, and evolved into using only the orings.
I think one reason for the teflon backup on the pistons was originally as a "wiper" ring to keep the oring and cylinder bore free from particulates (sand, etc.) that entered the chamber from the water. Especially useful when stupidly laying your rig on the sand in a few inches of water, and of course during surf entries. Main reason I grew to prefer Diaphragm type first stages... don't want grit in the works.
The older I get the better I was.

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