EPDM names a polymer family, not a compound. Peroxide-cured and sulphur-cured grades diverge above 120 °C.
Two seals may both be correctly described as EPDM and behave differently in a CIP circuit. The determining property is the cure system, which is rarely stated on an aftermarket part.
Peroxide-cured EPDM is rated to approximately 150 °C continuous and holds its compression set. Sulphur-cured EPDM is limited to approximately 120 °C, hardens in service, and is documented as able to alter the properties of fluids it contacts.
| Property | Peroxide-cured | Sulphur-cured |
|---|---|---|
| Continuous service | to approx. 150 °C; steam to 180 °C+ | approx. 120 °C maximum |
| Compression set | approx. 19% after 70 h at 100 °C | Hardens in service |
| Hot caustic (0.8–1.5% at 70 °C) Nitric (0.8–1.2% at 50–60 °C) | Minimal swelling | Degrades faster |
| Contact with product | Clean | May alter the properties of fluids in contact; blooming; metal staining |
Source: elastomer manufacturer material data for peroxide- and sulphur-cured EPDM compounds.
The final row has consequences beyond maintenance. A sulphur-cured compound in product contact in a dairy plant is a food-safety consideration rather than a wear item. It produces no fault condition and generates no work order.
Caustic wash at 70 °C and nitric wash at 50–60 °C fall inside the service range of both compounds. The compounds separate at steam and sterilisation temperatures, and the effect is cumulative across cycles rather than caused by any single cycle.
In service a sulphur-cured seat presents as a valve requiring attention more often than expected, on a line that stops briefly and repeatedly. Because each event is minor, it is rarely traced back to the compound purchased.
Aftermarket manufacturers produce correctly compounded dairy grades. Trelleborg's E7502 and E7518 are documented as suitable for milk contact and, under CIP conditions, superior to both silicone and HNBR.
Source: Trelleborg dairy elastomer material data.
The relevant question when a service kit is offered is therefore the compound designation and the cure system, rather than the manufacturer's name.
What is the compound designation, and is it peroxide-cured?
THE QUESTION TO PUT TO ANY SUPPLIER OF A SEAL KITThe elastomer is selected by ordering a different kit. It is a separate part rather than an option on the same part, and a butterfly valve kit exists in EPDM, silicone, FPM and HNBR as four distinct kits.
A butterfly valve service kit contains two disc bushings and one seal ring.
Source: hygienic valve service kit documentation.
For milk and dairy product under standard caustic and nitric CIP, EPDM is the normal selection, provided the compound is correctly specified. Silicone, HNBR and FPM each have defined applications.
The kit is identified from the valve size, the body type and the elastomer required. A photograph of the valve and of its identification plate is sufficient to identify the kit and to quote it.
Both are honestly called EPDM. Watch what the cure system does over six hundred CIP cycles.
| Figure | Value | Source |
|---|---|---|
| Peroxide-cured EPDM, continuous service | to approx. 150 °C (steam to 180 °C+) | Elastomer material data |
| Sulphur-cured EPDM, continuous service | approx. 120 °C max | Elastomer material data |
| Compression set, peroxide-cured | approx. 19% after 70 h at 100 °C | Elastomer material data |
| Sulphur-cured, product contact | May alter properties of contacted fluids; blooming; metal staining | Elastomer material data |
| Dairy-suitable aftermarket grades | Trelleborg E7502, E7518 | Trelleborg dairy elastomer data |
| Butterfly kit contents | Two disc bushings, one seal ring | Manufacturer service kit documentation |
| Seat replacement interval | NOT PUBLISHED | No manufacturer figure located. |
No universal replacement interval is published for hygienic valve seats or seal rings. Seat life is determined by the number of CIP cycles, the temperature, the product and the actuation frequency, all of which vary by plant and by valve position.
The practical method is to record seat life per valve position and establish the interval from the plant's own data. The manufacturer's channel has been asked whether any guidance exists expressed in CIP cycles. If a figure is provided it will be published here.
Frequently because it is a sulphur-cured EPDM rather than a peroxide-cured one. Both are correctly described as EPDM. Sulphur-cured is limited to approximately 120 °C continuous, hardens in service, and degrades faster in hot caustic and nitric CIP. Peroxide-cured is rated to approximately 150 °C and holds its compression set.
A correctly compounded EPDM is the standard dairy selection and outperforms silicone and HNBR under CIP. Sulphur-cured EPDM is documented as able to alter the properties of fluids it contacts, and can bloom and stain metal. The polymer family alone is not a specification.
EPDM, correctly specified, for milk and dairy product under standard caustic and nitric CIP. The other compounds have their own defined applications.
No universal interval is published. Seat life depends on CIP cycles, temperature, product and actuation frequency, and should be established from the plant's own records.
Parts: Hygienic valves · Seals & gaskets
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