Temperature is the constraint that catches most seal specifications out. A seat chosen for the normal operating temperature fails the first time the line runs hot after a dryer, or cold on a winter start-up. Getting the temperature envelope right — including the extremes, not just the average — is what keeps a valve on schedule.

Every elastomer has an upper limit above which it hardens and cracks, and a lower limit below which it becomes brittle and tears. Between those two points, performance still varies: a compound near its upper limit ages faster and takes compression set more readily than one in the middle of its range. A seal specified at the very edge of its envelope will have a short life even if it never technically exceeds the limit.

NBR typically serves from about −20 °C to +80 °C. It covers the overwhelming majority of dry bulk applications — cement, fly ash, feed, mineral powder at ambient — and it is the least expensive to replace. Above roughly 80 °C it hardens and loses elasticity quickly; below its lower limit it becomes brittle and may crack on the first stroke.

EPDM extends the useful range to roughly −40 °C to +120 °C, and adds excellent resistance to water, steam and ageing. For a plant that washes down lines, or where powder is damp, EPDM is the better seal even at moderate temperatures. It is the natural choice for feed mills and food plants.

Silicone reaches approximately −50 °C to +200 °C, the widest band of the common elastomers. Where powder leaves a dryer or a kiln and arrives at the valve still hot, silicone is often the only elastomer that will survive. The penalty is mechanical strength: silicone tears more easily, so it belongs in temperature-limited duty rather than highly abrasive duty.

The failure that surprises most plants happens not during steady running but during a transient. A line that runs at 60 °C normally may see 110 °C for the first minutes after a dryer restart. A seat chosen for 60 °C fails on that transient, and the failure is blamed on the seal rather than on the specification. Always specify against the maximum the valve will ever see, not the average it usually sees.

The same applies at the other end. Powder handled outdoors in winter, or product that has been chilled, can take a standard compound below its brittle point. When a cold start-up is followed by brittle fracture, the seat often splits rather than wearing gradually — a distinctly different failure signature from abrasion.

Above the silicone ceiling there is no elastomer answer. The choice becomes a metal-seated valve, or a different valve type entirely — and it is worth confirming that the rest of the line can tolerate the temperature before specifying the valve in isolation.

For abrasive mineral slurry rather than hot powder, the equivalent question is answered by sleeve compound rather than seat compound — see the pinch valve range and read the selection guide.