Loaded U-Cups derive their name from their "U" shape and the elastomeric energizer. They provide more effective low pressure sealing and seal on both the inside and outside diameters. U-Cup seals are often used for piston or rod seals due to the small gland space they require. U-Cups are usually specified for low speed, low pressure environments. They seal by means of the flared, flexible lip in contact with the rod or cylinder wall. Dynamic contact surfaces should have a finish of 8 - 16 RMS.