Abstract: The publication relates to a power converter according to the principle of the hot-air engine (Stirling engine), comprising a cylinder containing a main piston (4) and a displacement piston (3), each of which can be moved forward and backward on the axis of the cylinder and each of which possesses a piston rod assembly (20, 25) which is connected via connecting rods (17, 21) with a link system (21-24 or 17-19 resp.) to two parallel cranks (9) which rotate synchronously in opposite directions so that the displacement piston is moved phase-shifted to the main piston. The link system (21-24) of the main piston (4) comprises a frame element (24) which is rigidly connected to the latter's piston rod assembly (25) and has at least four journals (22,23) which are arranged symmetrically to the cylinder axis in a common plane perpendicular to the cylinder axis and which are oriented parallel to the crank shafts (9) and to each of which is linked a connecting rod (21).

Abstract: A hydraulic valve wherein the at least partially cylindrical internal surface of a cylinder or the at least partially cylindrical external surface of a piston in the cylinder is formed with a slot-shaped circumferentially extending outlet communicating with a plenum chamber. The other surface is formed with a circumferentially extending groove for a portion of a one-piece or composite sealing ring. The piston is movable in the cylinder between at least one first position in which the ring sealingly engages the slotted surface at one side of the outlet and at least one second position in which the ring sealingly engages the slotted surface at the other side of the outlet. That portion of the slotted surface which is adjacent the outlet is rounded, and that portion of the grooved surface which is adjacent the groove is also rounded.