Backup Rings backup rings STU-type backup rings are used in combination with radial-sealing O-Rings to prevent gap extrusion (extrusion of seals into the sealing gap). APPLICATIONS STU backup rings are often used in fluid technology, especially in valves and pumps. But they also have applications in many other areas of general industry, such as sealing ball valves. FUNCTION STU-type backup rings are endless elastomer rings with a concave cross-section, which provides the O-Ring with a more extensive contact surface. This enables the O-Ring to maintain its nearly round cross-section even under high pressure, and it is subject to very low deformation. This produces an improved sealing effect and increases the operating life of the seal. The STU backup ring has no sealing function itself. But its symmetrical profile allows it to be used in internal and external sealing systems. DIMENSIONS The currently available dimensions can be found on our website dichtomatik.fst.com or on our online ordering platform EASY. YOUR ADVANTAGES AT A GLANCE • High resistance to extrusion • High wear resistance • Improved sealing effect and increased operating life for the O-Rings • Nearly all dimensions for standard O-Ring measurements from stock FREUDENBERC INNOVATING TOGETHER