The piston seal type Aston Seals KDF is composed of: A seal element which assures a good reaction against shock pressure peaks and low friction in the low pressure range. The asymmetric lips are designed to differentiate the behaviour of the lips on the static and dynamic surfaces. The static lip is flexible, more sensitive to pressure fluctuations and it guaranties a wide contact area. The dynamic lip is shorter and stronger to concentrate load against the dynamic surface An angular wear ring which guides the piston in the cylinder and supports radial loads.