A control valve (1) for fluids, such as anaesthetic gases, has an inflow duct (18) surrounding an outflow duct (19). A valve diaphragm (13) is moved into and out of contact with a valve seat (20) around a mouth of the outflow duct (19), to open and close the valve (1). The diaphragm (13) is mounted to one end of a shaft (10), which extends through a casing (9) of the valve (1). At a far end of the shaft (10) is mounted a ferrous carrier (3) holding a permanent magnet (2). A coil (4) of electrical wiring is wound around a hollow cylindrical support (5) surrounding the permanent magnet (2). The carrier (3) has a cylindrical ferrous skirt (6) that surrounds the coil (4) in turn. The support (5) and coil (4) are fixed to the casing (9) via a back plate (7) of the valve (1). An electric current is passed through the coil (4), in either direction, generating an electromagnetic field. This interacts with the permanent magnet (2), pushing or pulling the shaft (10) longitudinally, and so displacing the diaphragm (13) into and out of contact with the valve seat (20), operating the valve (1).
