Sulfur vs Peroxide-Cured EPDM 1

[packdad]

I'm supposed to order new EPDM seats for some butterfly valves that are used for isolation in an HVAC system, and I'm told that peroxide-curing is preferrable to sulfur-curing. Why?

It should be noted that we would like to minimize compression set in this application, and from what little information I've found on the net, it appears that, at ambient temperatures, EPDM cured with peroxide/coagent actually has the same or more compression set than sulfur-cured EPDM. At higher temps, the peroxide/coagent cure does appear to have a significant benefit.

Also, let me slide one more question in here quickly: Would changing the seat durometer from 55-65 to 70-80 significantly impact the ability of the seat to seal? We are also considering this change as it has been recommended by the valve OEM. (Just trying to verify their recommendation.)

 

[btrueblood]

Packdad,

We've found peroxide-cured seals (O-rings) hold up in abrasion/wear and "aging" effects in water/glycol above 225 F. We also see the same or better compression set compared to sulfur-cured compounds, but have been told that the compression set is driven more by other parts of the formulation, and not so much by the type of cure.

I'm not sure about the "ease of seal" in a harder durometer, I could imagine a soft durometer would be better able to conform to the seat and thus make a tighter seal. But, a hard compound will not wear out as quickly; so if you can get a reasonable leak rate with it, use it.

 

[packdad]

I've now heard from several people that peroxide curing will give the same or better performance than sulfur curing, and that they're both about the same price, so I guess I'll stick with my request for peroxide-cured EPDM.

That's a good point about seal lifespan. I also think that a harder seal would provide a more even seal around the perimeter of the valve disk (and hopefully it would be a good seal).