Seal temperature selector
Right seal,
right heat.
Enter the coldest and hottest temperature your fluid sees. We show which seal compounds cover the range and recommend one — the same seal logic our configurator enforces.
Operating temperature range
- Buna-N
- -40°F to 165°F
- Standard service. Petroleum fluids.
- Polyurethane
- -40°F to 200°F
- High wear resistance. Heavy cycling.
- FKM (Viton)
- -20°F to 400°F
- High temperature. Aggressive fluids.
Carries the recommended seal and your high temperature into the configurator.
This selector matches a hydraulic cylinder seal compound to your fluid’s temperature range. Enter the coldest and hottest temperatures the cylinder will see, and it shows which of Buna-N, polyurethane, and FKM (Viton) bracket that range and recommends the most economical one that fits. Use it before you build, because a seal that is wrong for the temperature is the single most common cause of a leaking cylinder in the field.
Why both ends of the range matter
Seal selection is not about the peak temperature alone — it is about the whole span. An elastomer that is happy at 300°F may turn brittle and leak on a −10°F morning start; one that stays supple in the cold may soften and extrude when the fluid runs hot. A compound only qualifies when its rated low is at or below your coldest condition and its rated high is at or above your hottest. That is why this tool asks for a low and a high, not a single number, and why it fails a seal that misses at either end.
The three compounds
Buna-N (nitrile), rated about -40°F to 165°F, is the default for petroleum-based hydraulic fluid in ordinary service — good all-around sealing at the lowest cost. Polyurethane, to about 200°F, adds outstanding wear and extrusion resistance, which makes it the go-to for heavy-cycling rod seals even though its heat ceiling is only a little higher than nitrile’s. FKM (Viton) reaches 400°F and shrugs off aggressive fluids that would attack nitrile — the right call for hot systems and harsh chemistry, at a higher price and a slightly warmer cold limit (-20°F). Pick the least exotic compound that covers your range; there is no prize for over-speccing a seal the application never stresses.
Beyond temperature
Temperature narrows the field, but fluid type, duty cycle, and side load finish the selection. A biodegradable or fire-resistant fluid can rule out a compound the temperature alone would allow; a high-cycle application leans toward polyurethane for wear life; heavy side load may call for a specific seal geometry regardless of compound. This tool gets you to the right family fast, and the configurator carries your choice into a full build where our engineers confirm it against the rest of the spec.
Related tools
- Work out the force first with the force calculator.
- Check speed against seal limits with the cylinder speed calculator.
Seal temperature FAQ
How do I choose a hydraulic cylinder seal by temperature?
Match the seal compound to the full temperature range your fluid sees — cold start to hottest running. Buna-N (nitrile) covers −40°F to 165°F and is the standard choice. Polyurethane runs −40°F to 200°F with excellent wear resistance. FKM (Viton) handles −20°F to 400°F for high-heat and aggressive fluids. Pick the one whose range brackets both your low and high.
What temperature can Buna-N (nitrile) seals handle?
Buna-N is rated roughly −40°F to 165°F. It is the default seal for petroleum-based hydraulic fluid in ordinary service — good all-around performance at the lowest cost. Above about 165°F it hardens and loses life, which is where polyurethane or FKM take over.
When should I use FKM (Viton) instead of nitrile?
Use FKM when the fluid runs hot — up to 400°F — or when the fluid is aggressive (certain synthetics, phosphate esters, some chemicals) that would attack nitrile. FKM costs more and its low-temperature limit (−20°F) is not as cold as nitrile, so it is a deliberate upgrade, not a default.
Does polyurethane resist heat better than nitrile?
Polyurethane handles slightly more heat (to about 200°F) and dramatically better wear and extrusion resistance, which is why it is favored on heavy-cycling rod seals. It is not a high-temperature seal like FKM — for real heat you still step up to Viton.