How can you tell if the o-ring is silicone or rubber?

Hello,

I asked this question in the lube/grease thread and got no response. Maybe not many goes there or simply overlooked my question. So I am trying my luck here. When you purchased a light and it comes with the o-rings installed and also one or two spares. I read the lube/grease thread and some said don't use silicone lubricate on rubber o-rings. How do you know if the o-ring is silicone or rubber? Thanks.

dealgrabber2002 said:

I read the lube/grease thread and some said don't use silicone lubricate on rubber o-rings.

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You've got that backwards .. you can use silicone oil on most rubber O-rings; you shouldn't use silicone oil on silicone O-rings.

One caveat ... what is true for pure silicone oil is not necessarily true for silicone spray lubricants which are mostly petroleum solvent and propellant; some rubber compounds may not be compatible with those components.

"Rubber" is a pretty generic term. There are o-rings made of all kinds of materials, buna-n/nitrile, viton, EPDM, flourosilicone, PTFE, the list goes on. The problem comes in when you mix certain lubes with certain o-rings. Most have heard the phrase "like dissolves like". Putting petroleum jelly for instance on a petroleum based ring will dissolve the ring. Bad news.

The problem is that black o-rings all look virtually the same. If I set nitrile, viton, and EPDM o-rings in front of you, for example, unless you make o-rings for a living, you wouldn't know the difference. Your best bet is to refer to the materials that came with the light or contact the manufacturer.


Here is a great compatibility chart from McMaster Carr, where I have ordered o-rings from.

From my experience (not vast, though) silicone o-rings are usually softer than nitrile and are seldom black.

Yamabushi said:

One caveat ... what is true for pure silicone oil is not necessarily true for silicone spray lubricants which are mostly petroleum solvent and propellant; some rubber compounds may not be compatible with those components.

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True, but this can be overcome fairly easy: spray some silicone from the can into the cap and let volatile components evaporate for a couple of minutes. What remains in the cap is pure, thick silicone oil. Or use silicone grease instead.

Cheers

Several of my flashlights have silicone O-rings and they are red or orange in color and are very soft and pliable. I use a very light amount of scuba diver's pure silicone grease on all my O-rings (including the silicone) and rubber tail cap covers without any problems. However, YMMV as I've read it causes silicone to swell.
A small container of silicone grease cost less than $10 and will last you several years.

Yamabushi said:

You've got that backwards .. you can use silicone oil on most rubber O-rings; you shouldn't use silicone oil on silicone O-rings.

One caveat ... what is true for pure silicone oil is not necessarily true for silicone spray lubricants which are mostly petroleum solvent and propellant; some rubber compounds may not be compatible with those components.

Click to expand...

Thanks!

I work for a co. that part of the business is as an o-ring distributor and you can't tell for sure 100% though seldome are silicone o-rings black. Viton is easy becuase it has a dead fell with no bounce but with the rest it's not really possible. As far as the durometer or hardness goes you can pretty much make any material any hardness. It's best to just email the manufacturer.