Valve operator

A valve operator of the kind specified comprising a pole piece formed from magnetisable material, a hollow intermediate member formed from non-magnetic material, said intermediate member being secured in a fluid pressure proof manner to the pole piece, a further hollow member secured to said intermediate member at its end remote from the pole piece, said further member being formed of magnetisable material and secured to the intermediate member in a pressure proof manner, an end closure for the further hollow member, said pole piece and said members defining said fluid pressure proof compartment, an armature in said compartment, means whereby the pole piece can be secured to a fluid control valve, and a magnetising structure detachably mounted about the pressure proof compartment, said magnetising structure including an electric winding and the structure being arranged so that when the winding is supplied with electric current, said pole piece and the further member will be magnetically polarised establishing a magnetic field, the armature moving under the influence of the magnetic field towards the pole piece, said pole piece and said members defining a cylindrical outer surface, said magnetising structure being slidable over said surface and being angularly movable about said surface to a desired position, said magnetizing structure includes a rectangular core having apertures in its end members, said pressure proof compartment extending through said apertures so that the end members of the core are aligned with the pole piece and said further member respectively.