This type of seal is illustrated in Figure 8. At zero or low pressure, only the end of the sealing lip makes contact for sealing. When pressure rises, the fluid pressure causes the seal profile to expand radially, increasing the contact area for maintaining tightness. Concurrently, the back-up ring is designed such that its front (pressure side) end deforms to block any extrusion pathways. Finally, under high pressure, the seal profile deforms fully, while the back-up ring also deforms sufficiently to make full contact with the cylinder wall. In doing so, it creates a robust foundation that provides shear resistance and prevents extrusion.

Other combined seal configurations can operate with minimal (or even no) initial interference. In such cases, the contact force and area are established entirely by the fluid pressure itself.