Face o-ring for hydraulic piston

Lanza · Aug 24, 2021

I'm looking for machining information on this face o-ring groove on a hydraulic piston. The step is 0.070" deep, groove diameter 1.250", the shaft diameter is 1". The step has about a 10 degree taper. I assume the o-ring CS is 0.125".
Is there charts about these types of grooves for machining?

BoxcarPete · Aug 24, 2021

That's a bit of an oddball since it is a square groove with only one wall. You said face seal, so it will have a plate fixed to the top as seen in the picture, sealing pressure from the inside to the outside? In that case you want a -121 size (1.049" ID, 0.103" CS). If there's any possibility that it's something other than that, help me understand what else goes into the assembly.

atex57 · Aug 24, 2021

If this is on the surface that seals against the rod then use a -1xx series as BoxcarPete said. A -2xx series(1/8 CS) would overfill because of the shallow depth. Most pistons use a simple chamfer there.

Ed.

R. Dan · Aug 24, 2021

The face of the piston with the o-ring groove fits against the face of a turndown on the cylinder rod so the o-ring is trapped in between. The 10° taper in the groove seems a bit much as 5° is typical SOP for this application. The Parker book can help you figure all this out as you need a percentage of squeeze on the o-ring. I had proprietary charts for these groove sizes when I did this kind of design work but I can't pass this on because they were, well, proprietary.

BoxcarPete · Aug 25, 2021

So in that case I will affirm my recommendation of an AS 568 (or ISO 3601, they are the same size chart) -121 o-ring is your best bet for that existing part, but it is an aggressive 30% squeeze and a narrow 120% width, usually you'd see more like 20-25% and 140% width so just be wary of overfill.

10° might come from the inclusive angle of 5° per side? Looks like it might have been a homebuild, maybe whomever made it was doing some seat-of-the-pants engineering and ended up with that?

Chances are the -121 will be OK, it's not optimal but probably will work.

kenton · Aug 25, 2021

https://www.parker.com/Literature/O-Ring Division Literature/ORD 5700.pdf

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Face o-ring for hydraulic piston

Lanza

Aluminum

BoxcarPete

Stainless

atex57

Stainless

R. Dan

Cast Iron

BoxcarPete

Stainless

kenton

Stainless

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