Abstract: A hydraulically operated friction clutch wherein a spring-urged piston is provided to effect engagement of the friction elements, received in a casing mounted on the driving shaft for axial reciprocation relative to this casing and defining with this casing two coaxially arranged variable volume chambers communicating with each other, adapted to receive liquid under pressure the first one of said chambers is in permanent communication with a pressure liquid supply passage, while the other chamber is communicable via a valve means with a drain passage and the pressure liquid supply passage. The pressure liquid supply passage and the drain passage have a portion common to both of them, wherein the valve means is mounted so that the movable valve member thereof can reciprocate in a direction substantially perpendicular to the axis of rotation of the clutch, by which reciprocation it selectively connects the other chamber with the drain passage and with the pressure liquid supply passage.