The sealing mechanism of the CS is based on the hydrodynamic properties of the seal. The specially formed seal edge with a steep contact pressuregradient on the high pressure side and a shallow contactpressure gradient on the low pressure side ensures thatthe fluid film adhering to the piston rod is returned to the high pressure chamber on the return stroke of the rod. This prevents the micro-fluid layer, carried out of the high pressure chamber when the piston rod is extended, causing leaks.