O-rings, Buna N 70 or 90 Durometer

[AlanB]

Seems that the last several O-rings I have needed have been fair sized (about an inch) and skinny, like 1/16".

When they get to that OD in my kits they all start to get fatter in cross section.

The last one I needed was for the 3/8" quick connect on my 7308 loader.

The local hydraulic shop has a kit of the thinner cross section ones in a 90 durometer but not available in the 70 durometer (of course after he said he would get me one in 70)

He is willing to make me up any kit I want, and in some ways I feel stupid for even wanting a kit as he has always given me o-rings any time I have asked, but it sure would have been nice to have on the shelf when I cut that one and not had to wait a day for the shop to open. It was not a big enough deal to warrant calling him in after hours.

So the pointed question would be, what would be the harm of running the harder o-ring in the application calling for the 70? I am guessing increased possiblitly of leaks? and maybe price which would be inconsequential at some point to me.

 

[Wayne County Hose]

Hello Alan,

A 90 durometer o-ring won't seal as well. It may still do the job. It will also cut easier. I would run the 90 and ask him to order you a bag of the 70's. They are so cheap it ain't funny.

Andy

 

[3RRL]

Wayne is right. (Gee Wayne, for once we agree)
It's not as pliable as 70, but will surely work.

 

[AlanB]

Thanks Wayne and Rob.

I did not explain it well as I reread my post.

but I got the answer I needed.

I will just take the 90 durometer kit, and get him to give me all the same sizes in 70 durometer. (he has them all just not in a "kit" form)

So the advantage to the 90 would be longer wear in a rubbing type application?

 

[Brahmus]

A 90 durometer o-ring won't seal as well. Andy

What do you mean by "well"?

70 duro should be used most of the time as it's all around the best combination of properties.

softer compounds will seal better on rougher materials but will extrude easier at lower pressures as compared to harder compounds.

Yes the 90 is more abrasion resistant. And is more resistant to extrusion so will hold better at a higher psi.

In most situations the 90 will work just fine. But 70's are more common.

Also the "thickness" of an oring is classed in series.

0XX roughly .070"
1XX .103
2XX .139
3XX .210
4XX .275

The XX's are in series of diameter. The higher the number the larger the diameter. There for if you know your oring gap and diameter you can call ahead and give the o'ring #. It's universal.

 

[DieselPower]

Depends on the application. In some applications the 90 Durometer o-ring would be better. I actually have 5 kits. Standard Buna-N 70 Durometer kit, Viton 75 Durometer kit, Buna-N 90 Durometer hydraulic tube kit, Metric Buna-N 70 Durometer kit, Neoprene Air Conditioning kit and a Quad-Seal Buna-N 70 Durometer kit. What really sucks is I still ocasionally run into a manufacturer specefic size I don't have. Caterpillar and Cummins are great at having their own "special" sizes. Grrrrrr!

Depending on the hydraulic fitting application you might just find it actually came factory with a 90 Durometer. Most flat face, boss and split flange hydraulic fittings use 90's. Alan, if your using them on fittings the 90's would most likely be the correct ones.

Here's two examples from my o-ring supplier of hydraulic specefic 90 Durometer o-rings.
Catalog Item Display
Catalog Item Display

 

[Brahmus]

If you are in a pinch, you can always cut an oring to size and superglue it to get you out of a jam. I've done it several times. Has always worked but I've always changed it as soon as I was able to get the "correct" size.