Loaded U-cups’ name comes from their U shape and the elastomeric energizer. The seal results from a flared, flexible lip contacting the rod or cylinder wall. These U-cups allow for effective low pressure seals, both on the outside and inside diameters. Loaded U-cup seals frequently are used with piston and rod seals because they require a small gland space. Typically, they are specified for low pressure, low speed applications. Dynamic contact surfaces require a 8 – 16 RMS finish.