The Z-Seal is a squeeze type seal, combining the excellent sealability and low compression set of a resilient rubber lip with the greater anti-extrusion characteristics of a hard thermoplastic base. Under low pressure conditions, the sealing lip provides its own compressive seal force. As pressure increases, hydrostatic pressure is mechanically transmitted through the elastomeric seal element into the anti-extrusion base. The applied force then deflects radially in a controlled manner, closing the extrusion gap behind the sealing lip. Under this condition, maximum sealing effectiveness is achieved.