O'ring groove design
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    Default O'ring groove design

    Hi all,

    I was wonder how to design O'ring groove and how to know the requirements for rod sealing. I need to seal 1.125 in stainless shaft in a welded stainless bushing against water pressure (150psi). The rod will slowly rotate by hand, so no heat build up. I don't know where to start.

    Regards

    Philippe

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    Quote Originally Posted by phelop View Post
    Hi all,

    I was wonder how to design O'ring groove and how to know the requirements for rod sealing. I need to seal 1.125 in stainless shaft in a welded stainless bushing against water pressure (150psi). The rod will slowly rotate by hand, so no heat build up. I don't know where to start.

    Regards

    Philippe
    https://www.parker.com/Literature/O-...ORD%205700.pdf

    Start with chapter 5, section 27 (page 123) or section 28 (page 125).

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    Quote Originally Posted by phelop View Post
    Hi all,

    I was wonder how to design O'ring groove and how to know the requirements for rod sealing. I need to seal 1.125 in stainless shaft in a welded stainless bushing against water pressure (150psi). The rod will slowly rotate by hand, so no heat build up. I don't know where to start.

    Regards

    Philippe
    O-rings need lubrication, so they are not ideal for a rotating condition because the inside surface will wear out. So look for a lip seal style ring. Usually for low pressure, they will spec a softer durometer grade of rubber.

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    It will be rotating by hand like quarter of a turn a time.

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    For a one off, non-flight critical I'd use a 2-022 o-ring. The groove in the shaft would be 1.125"-0.140"+0.008"= 0.993" and make it 0.078" wide. The bore would be 1.125" and the shaft would be 1.120". You can flip the numbers if you want the groove in the bore. The groove in the bore is lightly more of a pain in the butt.

    Edit: Said 2-024 meant 2-022.

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    Quote Originally Posted by phelop View Post
    Hi all,

    I need to seal 1.125 in stainless shaft in a welded stainless bushing

    Sounds like a recipe for a seized up shaft and bushing. The two need to be dissimilar materials.

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    Quote Originally Posted by HuFlungDung View Post
    O-rings need lubrication, so they are not ideal for a rotating condition because the inside surface will wear out. So look for a lip seal style ring. Usually for low pressure, they will spec a softer durometer grade of rubber.
    Parker details allowable rotation in their handbook. It's not much, but it's not 0 either.

    If I recall correctly, I just emailed them asking for a copy and they sent me one free of charge. That was a couple years ago.

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    Quote Originally Posted by gbent View Post
    Sounds like a recipe for a seized up shaft and bushing. The two need to be dissimilar materials.
    Ha, just noticed that we have some stainless-on-stainless action here.

    Parker book says not to, but in a case like this you might be able to get away with using the o-rings as guides to keep the shaft out of contact with the sleeve. If your shaft is 1.1250.003" you should bore the sleeve to 1.1340.003" and groove two grooves to 1.3430.003" spacing them as far apart as you reasonably can. Then jam a pair of -219s in there, you want the ID size larger than the shaft to seat the OD of the seal against the groove so they will stay put on assembly.

    Stainless and water sounds like it might be a potable/food system. Get FDA EPDM o-rings and don't use lube if that is the case. Otherwise use standard grade EPDM and use a silicone grease, it will last longer. 70 durometer should be fine.

    That's what I'd do anyway.

    Edit to add:

    Quote Originally Posted by Kyle Smith View Post
    For a one off, non-flight critical I'd use a 2-024 o-ring. The groove in the shaft would be 1.125"-0.140"+0.008"= 0.993" and make it 0.078" wide. The bore would be 1.125" and the shaft would be 1.120". You can flip the numbers if you want the groove in the bore. The groove in the bore is lightly more of a pain in the butt.
    I'd recommend not using an -024 for the reasons I stated above. That o-ring will stretch around the shaft which is unideal for the application. You want the ring in compression, so it should be sized up in diameter. Additionally, the stainless seizing concern lends itself to a wider gap and two-ring approach as long as hand-twisting is the only load on the shaft which is much more forgiving with the larger cross-section of the -219.

    One more thought: Grooving the bore is the correct way to do a rotary seal. Only groove the shaft if you have no other way to get the job done.

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    Quote Originally Posted by BoxcarPete View Post
    Edit to add:



    I'd recommend not using an -024 for the reasons I stated above. That o-ring will stretch around the shaft which is unideal for the application. You want the ring in compression, so it should be sized up in diameter. Additionally, the stainless seizing concern lends itself to a wider gap and two-ring approach as long as hand-twisting is the only load on the shaft which is much more forgiving with the larger cross-section of the -219.

    One more thought: Grooving the bore is the correct way to do a rotary seal. Only groove the shaft if you have no other way to get the job done.
    Fat fingered the 2-024, meant 2-022, which is under compression. I'm not sure I'd classify this as a rotary seal. Why is a bore groove the only correct way?

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    Quote Originally Posted by Kyle Smith View Post
    Fat fingered the 2-024, meant 2-022. I'm not sure I'd classify this as a rotary seal. Why is a bore groove the only correct way?
    Fair enough, -024 has ID of 1.114" so with a shaft of 1.125" it would work in a bore-grooved design but -025 would be better, and a deeper groove with a -219 would be better yet! And as I mentioned before grooving the shaft is undesirable due to the black magic nature of seal design. You wouldn't think it matters much but the force balance ends up causing the o-ring to grip the shaft or slipping between the two, leading to "weird stuff" happening.

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    Quote Originally Posted by BoxcarPete View Post
    Fair enough, -024 has ID of 1.114" so with a shaft of 1.125" it would work in a bore-grooved design but -025 would be better, and a deeper groove with a -219 would be better yet! And as I mentioned before grooving the shaft is undesirable due to the black magic nature of seal design. You wouldn't think it matters much but the force balance ends up causing the o-ring to grip the shaft or slipping between the two, leading to "weird stuff" happening.
    My experience is primarily in 850psi (paintball) applications, but I haven't seen any difference between a grooved shaft or a grooved bore. I preferred the former if possible as it was easier to make and measure. I agree o-rings do odd things sometimes. I'm not clear on why a -025 with an I.D. of 1.176 would be better.

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    Quote Originally Posted by Kyle Smith View Post
    My experience is primarily in 850psi (paintball) applications, but I haven't seen any difference between a grooved shaft or a grooved bore. I preferred the former if possible as it was easier to make and measure. I agree o-rings do odd things sometimes. I'm not clear on why a -025 with an I.D. of 1.176 would be better.
    Is that a reciprocating or a rotating seal? For reciprocating it doesn't much matter, the downside to grooving the shaft is that it becomes a "piston" and needs to ride in a bore at least as long as the stroke. For rotational configurations, if it is on the rod it should be stretched or it won't assemble correctly. If it is stretched, heat from friction will cause it to expand but also weirdly contract, like a boa constrictor taking a deep breath while squeezing the life from you. That's why "weird stuff" starts to happen, it is gripping the shaft and also expanding into the groove and pushing against the OD. In this case it probably doesn't matter much since it's just hand-operated, but using the seals as a bushing will work better if they are grooved into the bore as well.

    The reason 1.176" ID is better than 1.114" is for the pre-assembly condition. Every o-ring needs to be biased one way or the other in its pre-assembled state (i.e. assembled to one mating component but not the other). Most commonly, a seal is stretched into a groove, this is the "piston" configuration so it is easy to get into the habit of spec'ing a 1~4% stretch on all o-rings. However, in the "rod" configuration the o-ring is installed into a groove and its OD needs to be seated against the groove, so it needs to want to be larger than the shaft size. It's hard to reconcile specifying a seal which is larger than the shaft and also supposed to interfere with it, but don't worry, once it fills the groove it's got nowhere else to go, and it'll squeeze the shaft.

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    Quote Originally Posted by Kyle Smith View Post
    For a one off, non-flight critical I'd use a 2-022 o-ring. The groove in the shaft would be 1.125"-0.140"+0.008"= 0.993" and make it 0.078" wide. The bore would be 1.125" and the shaft would be 1.120". You can flip the numbers if you want the groove in the bore. The groove in the bore is lightly more of a pain in the butt.

    Edit: Said 2-024 meant 2-022.
    I need to make the groove ont the bushing not the shaft !

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    Quote Originally Posted by phelop View Post
    I need to make the groove ont the bushing not the shaft !
    As has been said already, stainless on stainless will soon become a single part.

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    Quote Originally Posted by BoxcarPete View Post
    Is that a reciprocating or a rotating seal?
    Reciprocating.

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    Quote Originally Posted by BoxcarPete View Post
    https://www.parker.com/Literature/O-...ORD%205700.pdf

    Start with chapter 5, section 27 (page 123) or section 28 (page 125).
    I am by no means a o-ring guru.
    Where I work we rarely run into the need to machine o-rings. A few years back I received a print for a part from one of the imagineers here. He had basically designed his own o-ring groove that needed to be milled into a part. (apparently the one in question for this post will be turned). I looked in the Harvey tool catalog for a cutter. Found out Harvey makes tools for Parker spec o-rings.....after a brief conversation all o-rings here conform to the Parker spec and we use the Harvey tools.

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    Quote Originally Posted by toolsteel View Post
    I am by no means a o-ring guru.
    Where I work we rarely run into the need to machine o-rings. A few years back I received a print for a part from one of the imagineers here. He had basically designed his own o-ring groove that needed to be milled into a part. (apparently the one in question for this post will be turned). I looked in the Harvey tool catalog for a cutter. Found out Harvey makes tools for Parker spec o-rings.....after a brief conversation all o-rings here conform to the Parker spec and we use the Harvey tools.
    Makes sense to me. Only minor correction I have is that AS568 is the spec, and was not written by Parker (ISO-3601 is a metric translation of AS568 for size and contains additional surface finish and flash controls). However, Parker wrote the book, and it is damn near the ONLY book, on o-ring design. For further reading, consult James Walker (no affiliation) for their o-ring guide. EVERYTHING else is a copypasta of the Parker book or one of its subsections. I find that kind of funny, as I was told in school that plagiarism would have consequences when I grew up.

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    Whether the O ring is on the shaft or in the bore can make all the difference. I learned that when I tried to use hydraulic cylinders to measure jet engine thrust. Readings were jerky and erratic. Since this was a small jet engine, a Turbomecha Marbore IIF, the forces were not that high so O ring seals should work fine. The problem was simple once I got my head on straight. When you are using hydraulic pressure to move the piston, the pressure is trying to move it forward and is also pushing the O ring on the piston in the direction of travel. When the piston moves, it tends to roll the O ring in the opposite direction and the drag on the O ring is mostly just the friction against the bore. If instead you try to use the cylinder as a pump, both forces try to push the O ring into the clearance between the piston and cylinder, much like the action in a sprague clutch. It isn't an accident that the O ring in your hydraulic jack's pump is in the bore, not on the piston.

    To decide where to put the rings requires defining exactly what you want to do.

    Bill

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    25 years ago,I made a triple lifetime all stainless 125 foot hose reel.It has stainless on stainless gland.I used 3 oring grooves right next to each other. When you are cutting an oring groove,it only takes seconds to move your lathe carriage and make another.I filled the space between grooves with non toxic silicone grease. It hasn't seized up or leaked a drop in 25 years. Edwin Drnbeck

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    Quote Originally Posted by BoxcarPete View Post
    Ha, just noticed that we have some stainless-on-stainless action here.

    Parker book says not to, but in a case like this you might be able to get away with using the o-rings as guides to keep the shaft out of contact with the sleeve. If your shaft is 1.1250.003" you should bore the sleeve to 1.1340.003" and groove two grooves to 1.3430.003" spacing them as far apart as you reasonably can. Then jam a pair of -219s in there, you want the ID size larger than the shaft to seat the OD of the seal against the groove so they will stay put on assembly.

    Stainless and water sounds like it might be a potable/food system. Get FDA EPDM o-rings and don't use lube if that is the case. Otherwise use standard grade EPDM and use a silicone grease, it will last longer. 70 durometer should be fine.

    That's what I'd do anyway.

    Edit to add:



    I'd recommend not using an -024 for the reasons I stated above. That o-ring will stretch around the shaft which is unideal for the application. You want the ring in compression, so it should be sized up in diameter. Additionally, the stainless seizing concern lends itself to a wider gap and two-ring approach as long as hand-twisting is the only load on the shaft which is much more forgiving with the larger cross-section of the -219.

    One more thought: Grooving the bore is the correct way to do a rotary seal. Only groove the shaft if you have no other way to get the job done.
    Thanks, the shaft will be rotating by hand.


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