Abstract: Actuators and valve-actuator combinations are disclosed which require low power for actuation, and which are particularly suitable for use to control a valve associated with a pipeline. Such an actuator (20) comprises a thrust member (26) moveable between two end of travel positions, an annular rotor having magnetic poles, an annular magnetisable stator having at least one winding and poles with which the rotor poles are aligned in each of a plurality of rotational positions of the rotor relative to the stator, and a drive connection between the rotor and the thrust member which is adapted to convert rotational movement of the rotor into linear movement of the thrust member. The actuator is able to hold its position using minimal energy, and may be located within or around an associated pipe.

Abstract: An electromagnetic actuator status defines two pairs of poles between which an elongate magnetisable armature can see-saw through a mid position between two home positions defined by two of the poles. A closed low reluctance path in each home position includes a permanent magnet which keeps the armature in either home position. An electromagnet is energised by a current pulse, to repel the armature from one home position and attract it to the other. Resilient energy storage means resists the final movement of the armature towards each pole. A non-magnetisable curved central region of the armature makes rolling contact with a complementary curved surface with the stator to cover and uncover openings therein. The stator is housed within, or forms a fluid chamber and fluid supplied thereto can be delivered selectively through one or the other of the two openings.