The invention features, (i) a fan-shaped or otherwise axially deformable washer structure (4D) between a screwed element (5,5A) and a valve body member or coil jacket (3); (ii) a conical preferably self-tapping or self-cutting, a fine, screw thread (8) moving with the element; (iii) a thin valve carcass which may be distorted or even broken by normal screw-in pressures encountered, or by heating-up effects; (iv) the washer forming part of or being integral with the magnetic circuit of the solenoid; (v) a return spring (7A) in the gap (7), between the two armature parts (5,6) e.g., lodged in recesses in the adjacent faces thereof; and (vi) an annular recess (9) in the periphery of the "fixed" armature part (5), to accommodate an O-ring, if satisfactory fluid sealing should require it; also a further axial interval (10) to accommodate a certain freedom of screw-in.