Abstract: A solenoid designed to operate immersed in a fluid containing magnetic particles of debris, and having a movable armature slidable toward and away from a fixed core within a bobbin carrying the electromagnetic coil. The bobbin is provided with internal flutes defining longitudinal passages opening at both ends of the solenoid for conducting magnetic particles or debris out through the passages as the solenoid armature moves toward the core.

Abstract: A solenoid is disclosed in which a ferromagnetic shield substantially surrounds the circumferential surface of the coil in order to provide a high-permeability flux path on the coil exterior. The shield is formed by a ferromagnetic collar and the body part of a bracket. The ferromagnetic collar extends partially around the coil, and the body part of the bracket faces a longitudinal opening in the ferromagnetic collar. The ferromagnetic collar is embedded in a molded epoxy encapsulation, which is found to be reinforced by the collar. Alternatively, the shield can be formed exclusively of a ferromagnetic collar that extends substantially around the entire periphery of the coil.