Full definition
A comprehensive term for all sealing elements used within hydraulic systems — cylinders, pumps, motors, valves, and fittings — operating at pressures from 70 to 350+ bar with mineral oil, synthetic, or water-glycol hydraulic fluids. A typical hydraulic cylinder contains 5-8 seals: piston seal (main pressure seal on piston), rod seal (retains pressure at rod exit), wiper/scraper (excludes external contaminants from rod), wear rings/guide bands (support piston and rod, prevent metal contact), buffer seal (reduces pressure spikes reaching the rod seal), and static O-rings (all non-moving joints). Materials: polyurethane PU (best for mineral oil at -30 to +80°C — dominant for piston and rod seals), NBR (standard, economical, -30 to +100°C), FKM (high temperature or aggressive fluids, -20 to +200°C), and PTFE/bronze compound (lowest friction, broadest temperature range). Seal profile design must match: operating pressure, fluid type, speed, temperature, and cylinder bore/rod finish. Per ISO 5597 (cylinder groove dimensions), ISO 6020/6022 (hydraulic cylinders), and fluid compatibility per ISO 6743. System cleanliness (ISO 4406) directly impacts seal life. Brands: Parker, Trelleborg, Hallite, SKF (Economos), Freudenberg.