Step seal. Piston & Rod configurations
Used alone, in pairs, or in conjunction with another sealing element, step seals buffer the primary seal from pressure spikes. Typically a PTFE based seal lip is energized against the dynamic surface using an o-ring. Profile shape allows back-pumping of intermediate fluid to avoid pressure traps.
Special Applications
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Fun fact - 2 seals in 1!
Over time the thermoplastic lip profile can wear flat, at which point this seal functions as a cap seal!