Parback® backup ring with a curved cross-section.
Parbaks are contoured on one face to minimize distortion of the o-ring when under pressure. Parbaks should be installed with the contoured face against the o-ring, but reversal does no harm.
Hytrel backup ring with a flat cross-section.
Excellent extrusion resistance and tolerance to fluids such as phosphate esters, hydraulic oil, and water.
Solid Urethane backup ring with a flat cross-section.