The piston seal type Aston Seals KD 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. They can also be used in back-to-back arrangement for double acting piston.