Start with the fluid, not the catalog
The single biggest cause of premature O-ring failure isn't pressure or squeeze — it's chemical incompatibility. Before opening a size chart, list every fluid the seal will contact, including cleaning agents and incidental exposure during maintenance.
The four-question filter
FITCO's application engineers run every enquiry through four questions: What fluid(s) contact the seal, continuously and incidentally? What is the temperature range, including transient spikes? Is the application static or dynamic? What standard or certification does the end customer require (NORSOK, FDA, WRAS)?
Quick reference
Mineral oil and hydraulic fluid at moderate temperature: NBR is almost always correct and most economical. Push past 150°C, into aromatic fuels, or into oil & gas sour service: move to FKM. When the chemical list gets unpredictable — solvent rotation in a process reactor, for instance — FFKM is the only compound that removes the guesswork. Water, steam or outdoor weathering: EPDM, but only if oil contact is impossible. Food or pharma contact: FDA-grade silicone or EPDM depending on temperature.
When in doubt, send the fluid name
Compatibility charts are a starting point, not a guarantee — compound formulation varies between suppliers. FITCO's technical team cross-checks every non-standard fluid against our compound library before quoting; send us the exact trade name and concentration rather than a generic category.