Rotary inlet/exhaust valve for internal combustion engines having seals employed to minimise gas leakage around cylindrical valve rotor (12) which rotates with a radial clearance gap within a receiving bore of the engine. Rotor (12) comprises a main cylindrical body (40) having a rectangular exhaust port (48) formed on the circumferential surface of rotor (12) with angular spacing from inlet port (46). Sealing elements (70, 80, 90) are received in respective grooves (60, 64, 68) formed on the circumferential surface and arranged to bridge the radial clearance gap to create over each discrete surface zone, discrete volume sectors that rotate with rotor (12). Each annular sealing element (70) consists of a pair of sealing rings. Rotor (12) incorporates a pressurizing system arranged to selectively direct a pressurized fluid in between each sealing ring pair (70) to bias the rings in axially opposite directions to prevent high pressure gases from breaking the seal between the flanks of sealing elements (70) and the end faces of sealing elements (80, 90). This prevents ring seals (70) from moving away from the side surfaces of groove (60), and hence away from the end faces of sealing elements (80, 90).