O ring material

[coniston]

I call upon your esteemed knowledge (please) in making a material choice for O rings in steam circuit.

Researching O ring material for the steam pipe joint to wet header there are (as I see it) three alternatives being Viton, Silicone and EPDM. All seem to have similar temperature rating on the face of it. Here are the details from my copy of the Parker precision O ring handbook I have.

Viton:
Temperature resistance - up to 200C
Not compatible with super heated steam

EPDM:
Temperature resistance - up to 150C (maximum 200C in water and water/steam)
Chemical resistance - water / steam
Not compatible with mineral oil products

Silicone:
Temperature resistance - up to +210C
Chemical resistance - Water to 100C
Not compatible with super heated water / steam over 120C

So for this application my leaning is towards EPDM? Any other thoughts please.

Thanks
Chris D

[Roger]

Personally I'm using Silicone for most of my Steam applications because it's flexible and will withstand high temperatures. Viton is also suitable, but it's harder so not as compliant for things such as valve stems. I also find the finish to be grainy compared to other materials.

I'd take the limitations with a pinch of salt personally. The datasheets are concerned with long term exposure while maintaining unaltered properties of the materials. Our usage is for relatively short term exposure and subtle changes to the properties aren't of great concern to us. If we need to change our O rings every few years it's not a big deal.

Ross (suctionhose) has used Viton for steam seals for a very long time without any issues as long as there is lubrication.

[Gary L]

Nov 10, 2020 23:52:49 GMT Roger said:

Personally I'm using Silicone for most of my Steam applications because it's flexible and will withstand high temperatures. Viton is also suitable, but it's harder so not as compliant for things such as valve stems. I also find the finish to be grainy compared to other materials.

I'd take the limitations with a pinch of salt personally. The datasheets are concerned with long term exposure while maintaining unaltered properties of the materials. Our usage is for relatively short term exposure and subtle changes to the properties aren't of great concern to us. If we need to change our O rings every few years it's not a big deal.

Ross (suctionhose) has used Viton for steam seals for a very long time without any issues as long as there is lubrication.

Silicon is indeed good where softness is an advantage (like valve glands) but the downside is it is easily cut, such as when removing (or inserting) the valve stem, especially when wet. So keep some spares for any dismantling. But that is a good plan anyway when dealing with O-rings.

I agree about the baffling nature of the data sheets; to go by the descriptions none of the materials are ideally suited to use with high pressure steam. But we do, and they always seem to work.

Gary

[JonL]

I would estimate I've steamed around 20 hours with my silicone o-ring piston rings and when I last inspected them they looked as good as when they went in. As mentioned, I'm more likely to kill them removing and inserting than just letting them be.

[coniston]

Thanks Roger, Gary and Nobby for your responses, taking all things into account I will go with Silicone as the higher dry temperature resistance will outweigh any benefit the other materials may have regarding steam suitability.

Thanks

Chris D