O-Rings - Standard, Metric, and ???

I have little red boxes of standard and metric size O-rings, yet time and time again nothing seems to be a perfect match, what series of O-rings am I missing?

Todays job was fixing a hydraulic leak on a cheap, probably imported from China log splitter, the control lever rotates in a bushing. Pulled bushing, O-rings as I suspected, nothing in metric or standard sets match either the internal or external O-ring. I found something close for the internal one, re-used the external one, not holding my breath.

Just plain black Buna N, have resorted on a few occasions to use the green AC O-rings just because size was right.

https://www.amazon.com/Small-Parts-Sizing-Inches-Plastic/dp/B01414HQNE

These are pretty handy to have in the shop.

+1 Those kits seem to fit everything except what I'm working on.

Not sure that is going to help if nothing in the boxes matches. Do I need to buy better sets of O-rings, or sets with sizes other than standard/metric?

Today the external ring cross section was much thinner than anything in box, the internal ring seemed to have a slightly larger OD than anything in box, not sure if it was stretched, so used the closest I could find.

That cone thing covers about 325 different O-ring sizes. Then you have materials and durometer.

My O-ring kit is a seal supply house. It is about 100,000 square feet and 40 feet tall.

I have never ever had an o-ring kit in a box. I couldn't fathom what I need ever being in such a thing.

Garwood said:

That cone thing covers about 325 different O-ring sizes. Then you have materials and durometer.

My O-ring kit is a seal supply house. It is about 100,000 square feet and 40 feet tall.

I have never ever had an o-ring kit in a box. I couldn't fathom what I need ever being in such a thing.

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I realize to cover every size possible it would require a warehouse, but such a thing does not exist anywhere near me. If we rule out proprietary sizing, and anything over 1.5", is it possible to get down to 4?, 5?, 6? sets to cover more than the 2 that clearly cover less than 50% of the O-rings I encounter?

IME there are a lot of ''non standard'' Orings used - I don't know about now, but back in the day John Deere were renowned for being awkward.

Made it an almighty PITA when stocking service trucks, ..........get out to a breakdown in the middle of a bloody great field miles from anywhere and the supply houses shut and you're screwed for a 20c Oring, .....while of course the next crop HAS to go in because there's a break in the weather

There is nearly an infinite number of o-ring sizes, even below 1.5" OD. A kit is just somebody's guess as to what sizes you'll need.

Buy a good O ring kit I have tried to use them cheap kits from the parts house and they are just not very good. They don’t fit right and the quality is just not there for high pressure hydraulics. I keep a large supply of o rings on hand, they are priceless when you need one. I usually buy them at McMasters, they also have nice kits.

so what size did you need?

dian said:

so what size did you need?

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X2.........? ID and cross section (or width of oring groove)

It depends on the type of equipment you are working on. In the pneumatic industry we use primarily Parker #2-Series, 2-001, 2-002, etc. I've had to build my own kits for the common materials and durometers. I have one for Cast Urethane, NBR, Viton, and EP in both 70 and 90 durometer Shore A. They are expensive kits to build. I typically buy through Zatkoff and have asked the salesman to build the kits, but I'd imagine the demand is low, at least from their perspective. They are in the game of selling 100,000's of one size to manufacturers.

O rings come in three sizes.
Too big.
Too small.
And doesn't fit.

The oilfield is no different, we have a few special sizes that nobody stocks. We have to pay to get molds made, and make sure we don't runout, too.
Parker used to have a 500 series O=ring that were their specials, you usually match up to them provided they had any in stock. Of course, it may not come in the material you want. The last time I looked at their website, I couldn't find the 500 series listed, so I guess it is obsolete now.
Another thing we do with larger O-rings if one does falls between sizes, we go to the next size larger for a internal groove or go down a size if used in a external groove. In your case, the groove is not deep enough for a standard O-Ring, put the spool up in the lathe and deepen the groove for a standard O-ring. Ken

The standard sizes cover the majority of things, IME. If you're getting into metric, your chances go way down of finding an exact match because the sizes are just going to be some "round" number of mm that the designer pulled out of his ass.

Comparing old o-rings to standard sizes is always a bit dicey. You'd best round down on the ID because most of the time the ring has absorbed a bit of something (8% is very typical) which increases its size. At the same time the cross-section has been squeezed and taken a compression set so it won't look like it's swollen or larger and you'll be left scratching your head.

That said, you can cheat and get away with a lot in the o-ring world. The key point to remember is that the seal is behaving like a constant volume incompressible fluid with an outrageous amount of viscosity so it doesn't flow through the gap. Some applications of this concept:

Best thing to do if your closest cross-section is too fat is to use the next smaller ID. That will stretch the o-ring and thin the cross section some. Once you get to the right amount of stretch it should work for a while. Depending on the material and how much you had to stretch it, this will decrease its service life anywhere from a little bit to quite a bit.

If nothing fits because the idiot who designed it made the width of the groove the same as the depth, you're in a bit of trouble. Only thing you can do is widen the groove so you can get some squeeze on the rubber and leave it some space to spread out.

If you can finagle it into a range of 10-30% squeeze, less than 90% volume fill, and preferably less than 5% stretch you should be OK.

I used to work at Hercules Sealing Products out of Clearwater FL. We had CNC machines that could custom machine SEALS. We also has 300K worth of O-Rings in Stock. They have a new facility on Louisville HY that can ship UPS late and still make it to you. They also have a large kit and O-Ring Boss, Flange, ... kits. www.herculesus.com

One of my customers has a great store in Washington. The O-Ring Store LLC, We make getting O-Rings easy!

Good Luck
Michael :- )

dian said:

so what size did you need?

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The one I replaced measures .560 ID, .110 cross section, I'm hanging onto it in case I need to put it back in, visually it looks fine. Splitter sat unused for a year without leaking, pretty sure all the fluid leaked out in past year, I really expected to find a cracked seal.

I will look at McMaster and Hercules kits.

dalmatiangirl61 said:

The one I replaced measures .560 ID, .110 cross section, I'm hanging onto it in case I need to put it back in, visually it looks fine. Splitter sat unused for a year without leaking, pretty sure all the fluid leaked out in past year, I really expected to find a cracked seal.

I will look at McMaster and Hercules kits.

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This covers pretty much everything related to o-rings in the US.
0.103" and 2.65mm (0.104") are common.

https://www.parker.com/Literature/O-Ring%20Division%20Literature/ORD%205700.pdf

dalmatiangirl61 said:

The one I replaced measures .560 ID, .110 cross section, I'm hanging onto it in case I need to put it back in, visually it looks fine. Splitter sat unused for a year without leaking, pretty sure all the fluid leaked out in past year, I really expected to find a cracked seal.

I will look at McMaster and Hercules kits.

Click to expand...

You don't suppose that it should be 14 X 3 mm? I have bought O-rings (10,000 pcs) that we have to grind the OD as the cross section is not round.

FredC said:

You don't suppose that it should be 14 X 3 mm? I have bought O-rings (10,000 pcs) that we have to grind the OD as the cross section is not round.

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That's what's so fun about part matching used parts. 14x3mm translates to 0.551x0.118" which would be a possibility if the part looked anything like either of these:




Especially if you go after the cross section and get two different numbers axially and radially, we might suspect that.

However, going on my experience, those numbers sound like a -113 size, 0.549x0.103" with some fluid swell to it. Based on the measured numbers and the tolerance band, somewhere from 6-11% swell, right in line with NBR used in hydraulic oil. If the cross section still looks round I'd go with the -113 for a replacement.

If you can measure the groove I can add additional education to my guesses

But if the o-ring still looks fine you might double check for any flaws or scratches on the mating parts, doesn't take much of one in the axial direction to neuter the sealing performance of an o-ring.