Solenoid construction

A solenoid valve comprising a cylindrical armature formed from magnetizable material and having a plurality of axially spaced annular grooves formed in its outer peripheral surface, the grooves lying in planes respectively perpendicular to the axis of movement of the armature, an electrical winding comprising a plurality of annular disc shaped winding portions surrounding the armature, each winding portion lying between an adjacent pair of a plurality of annular discs formed from magnetizable material and surrounding the armature, adjacent discs being in contact with each other at their outer edge portions, there being as many annular discs as there are grooves on the armature, the winding portions being arranged so that in use when electric current flows therethrough adjacent discs will assume opposite magnetic polarity, the magnetic flux effecting movement of the armature, each of said discs being divided into at least two parts whereby the discs can be assembled about the armature with the inner edges of the discs extending into the respective grooves the thickness of the inner edges of the discs being chosen in relation to the width of the grooves so that in the de-energised condition of the winding the discs are offset in the axial direction in relation to the grooves and a valve closure member movable by the armature.