Full definition
A broad category of sealing elements that use a flexible lip — a thin, precisely shaped edge of elastomer, PTFE, or polyurethane — pressed against a mating surface (shaft, rod, or bore) to prevent fluid leakage and/or contaminant ingress. The lip's flexibility allows it to maintain contact despite shaft runout, eccentricity, and surface imperfections. Major types: (1) Radial lip seal / oil seal — lip contacts rotating shaft circumference; retains oil/grease and excludes dirt (see Oil Seal entry). (2) Piston seal — lip contacts cylinder bore; seals hydraulic/pneumatic pressure on a reciprocating piston. (3) Rod seal — lip contacts reciprocating rod; retains cylinder pressure. (4) Wiper/scraper seal — stiff lip scrapes contaminants from rod before they enter the cylinder. (5) V-ring seal — axial lip rotates with shaft, sealing against a stationary face. Lip materials: NBR (standard oil service), FKM (high temperature/chemicals), PU (high pressure/abrasion), and PTFE (highest speed/chemical resistance). The lip profile, contact angle, and interference are precisely designed for each application. Per ISO 6194 (rotary), ISO 5597 (hydraulic cylinder), and ISO 6195 (pneumatic cylinder).