(1) Inside a cheap ebay solenoid water valve from YouTube
The video above demonstrates different component within a typical solenoid valve.
Any current carrying coil will produce a magnetic field (for example) to exert a mechanical force of attraction or repulsion on any magnetic object. The effect is the same as produced by permanent magnet but in this case of a current carrying coil, the field could be made to turn ON or OFF as desired by switching the current through the coil ON or OFF. This magnetic effect find applications in magnetic relay and solenoid.
A solenoid is a device that produces mechanical motion when a current carrying conductor coil receives electric current. The movable portion of a solenoid is the armature. A relay is a solenoid set up to actuate switch contacts when its coil receives electric current. Pull-in current is the minimum amount of coil current needed to actuate a solenoid or relay from its “normal” (de-energized) position. Drop-out current is the maximum coil current below which an energized relay will return to its “normal” state.
Armature is the movable magnetic object, and you can move most armatures with either direct current (DC) or alternating current (AC) energizing the coil. The polarity of the magnetic field is irrelevant for the purpose of attracting an iron armature. you can use solenoids to electrically open door latches, open or shut valves, move robotic limbs, and even actuate electric switch mechanisms.