US Patent 7131454 Piston sealing mechanism for liquid additive injection pump

A system for injecting a predetermined amount of a secondary fluid into a primary fluid stream uses a liquid additive injection pump driven by a fluid powered motor driven by the primary fluid stream. The liquid additive pump has a reciprocating piston movable within a cylinder between upstroke and downstroke positions to meter the secondary fluid and a piston sealing mechanism comprising spaced-apart distal and proximal sealing elements. The distal piston-sealing element is flared in the direction of piston downstroke and the proximal piston-sealing element is flared in the direction of piston upstroke.