Hydraulic seals are dynamic-working gaskets which are designed for sealing on axial moves in pistons. Give good results on horizontal move and cylinders that have a big space between piston, or extensive tolerance. However they are one way sealing element, with assembling of two on their bottom sides, they provide both way sealing which there is not need to air in the middle part. They are suitable for especially at low and middle pressure. They are much sensitive for cutting and abrasion if materials have much tensile. It is recommended to have a short lip height on percussive working, or if pressure is high. Friction force depends on axial velocity. Whether the velocity increases, friction force decreases.