Full definition
A precision sealing device for rotating shafts (pumps, agitators, compressors, mixers) that prevents leakage by maintaining two highly polished, flat faces — one rotating with the shaft (rotary face) and one stationary in the housing (stationary face) — in intimate contact with a thin lubricating fluid film between them. This controlled-leakage design (typically <1 ml/hr) has largely replaced compression packing for pumps due to dramatically lower leakage, lower shaft wear, and lower maintenance. Components: rotary face (typically silicon carbide or carbon/graphite), stationary face (silicon carbide, ceramic, or carbon/graphite), secondary seals (O-rings, elastomer bellows), spring mechanism (single or multiple springs, metal bellows), and drive mechanism (set screws, pins, or clips). Types: single seal (one set of faces — standard for most pumps), double seal (two sets of faces with barrier fluid — for hazardous/toxic fluids), and cartridge seal (pre-assembled, pre-set unit — simplest installation). Per API 682 (refinery pumps — the primary standard), EN 12756 (European), and DIN 24960. Face materials must be compatible with the process fluid. Brands: John Crane (market leader), Flowserve, Burgmann (Eagleburgmann), AES.