Four elastomer families cover the overwhelming majority of powder and bulk solids valve applications: NBR, EPDM, silicone and FDA-grade compounds. Each has a clear best-fit area, and choosing between them is mostly a matter of matching the material's weakness to the thing your medium does worst.

NBR is the workhorse seal material. It resists oils, greases and many hydrocarbons well, holds its shape under compression, and is inexpensive to replace. Typical service range is around −20 °C to +80 °C. It is the default seat in our powder butterfly valve range for cement, fly ash, feed and general dry bulk. Do not specify it for hot product above roughly 80 °C or for solvent-bearing media.

EPDM trades oil resistance for excellent resistance to water, steam, ozone, weathering and ageing, with a useful range extending to around +120 °C. Food-grade grades are readily available. For humid, wash-down or steam-adjacent lines — feed mills and food plants especially — EPDM is usually the better choice than NBR.

Silicone holds flexibility across the widest temperature band of the common elastomers, roughly −50 °C to +200 °C, which makes it the answer when powder arrives hot from a dryer or kiln. The trade-off is mechanical: silicone tears more easily than NBR or EPDM, so it suits temperature-limited duty rather than highly abrasive duty.

For food and pharmaceutical powders the seal must be a compliant, non-toxic, non-absorbing compound that can be cleaned. FDA-grade compounds are usually supplied in white so contamination and wear are visible on inspection. They cost more and are not more abrasion-resistant than a standard compound — they are specified for compliance, not wear life.

Temperature limits depend on the specific compound rather than the family, so confirm the actual figure for the medium you are handling rather than assuming a generic number.

No compound compensates for a valve used outside its design envelope. A seat that is throttled against abrasive powder, or held closed under excessive actuator pressure, will fail regardless of what it is made from. Choose the material properly, then operate the valve properly.

The same logic applies inside a pinch valve, where the sleeve takes the place of the seat. We supply sleeves in natural rubber and food-grade EPDM — see the sleeve materials guidance for which to specify. Compare valves in the bulk solids selection guide or browse the full range.