Question

draw a sketch for wet armature solenoid. describe how a wet armature solenoid works.

Answer 1

Like mechanical or pilot actuators, solenoids work against a push pin, which in turn actuates a spool. There are two types of solenoid design used to dissipate the heat developed in electric current flowing in the coil. The first type dissipates the heat into surrounding air and is referred to an “air gap solenoid”. In the second type “wet pin solenoid”, the push pin contains an internal passage way that allows the tank port oil to communicate between the housing of the valve and the housing of the solenoid. Wet pin solenoids do a better job in dissipating heat because the cool oil represent a good heat sink to absorb heat from the solenoid. As the oil circulates, the heat is carried into the hydraulic system where it can be easily deal with.

A wet armature solenoid consists of a coil , rectangular frame, pushpin , armature (plunger) and tube. The coil is surrounded by the rectangular frame and both are encapsulated in plastic. In the encapsulated unit, a hole runs through the coil center and two sides of the frame. The tube fits within this bore as it is screwed into a directional valve body.
Housed within the tube is an armature which is bathed by system fluid through the tank passage within the directional valve. This accounts for the "wet armature" identification.

Working:

With an electrical current passing through its windings, a magnetic field sets up around the coil. This magnetic field is intensified by the rectangular iron path surrounding the coil and also by the armature in the coil center.
As a wet armature coil receives electric current, the movable armature is partially out of the coil. The magnetic field generated from the current attracts the armature pulling it in. Directional valveshifts as the armature hits a pushpin in contact with the valve spool. With spool shifted, armature is fully centered within the coil resulting in the coil magnetic field traveling completely through an iron path.

Iron is an excellent magnetic conductor; the oil surrounding armature and pushpin is a poor magnetic conductor. Wet armature solenoid operation depends on the magnetic field pulling in the armature reducing the high resistance gap in the coil center. As the armature moves in, the gap gradually decreases causing solenoid force to become increasingly stronger. Solenoid force is greater with the armature pulled in than out.