A hydraulic master cylinder having a cylinder body (1) with a piston (3) slidable therein. The piston carries a sealing assembly (20) to permit pressurization of a pressure chamber (6) and fluid recuperation upon retraction of the piston. The sealing assembly includes a first seal (23) of relatively hard material slidable against the internal cylinder wall and a relatively resilient second seal (25) arranged to act between the sealing surfaces of the piston and the first seal to provide a fluid tight pressure seal during pressurization of the chamber.