Solenoid Valve

Overview

A solenoid valve switches flow with electricity instead of a hand or a motor. A current through a coil builds a magnetic field that pulls a steel plunger off its seat; cut the current and a spring pushes the plunger back to shut the valve. With only one moving part and no operator, it opens or closes in milliseconds, which is why it is the actuator behind everything from a washing-machine fill to a pneumatic manifold to an irrigation zone.

The Valve Body & Ports carries the ports and the seat. The Solenoid Coil sits above it and drives the Plunger Assembly up and down. The Electrical Connection brings coil power in from the controller, the Manual Override lets the valve be opened by hand when power is out, and on larger valves a Pilot Diaphragm does the heavy lifting the coil cannot.

How it works

In a direct-acting valve the coil pulls the plunger straight off the orifice, so the magnetic force alone has to overcome the line pressure on the seat. That limits direct-acting valves to small ports. The Copper Winding is wound on a Coil Bobbin around a sealed Core Tube, and a steel Magnetic Yoke wraps the coil to concentrate the flux on the Plunger / Armature. When energized, the plunger lifts its Seat Seal off the Valve Seat / Orifice; when de-energized, a Coil Spring reseats it.

To switch larger flows on the same modest coil, a servo (pilot-operated) valve borrows the line pressure itself. Here the plunger opens only a tiny pilot port in the Pilot Diaphragm. Bleeding that port drops the pressure above the diaphragm, and the higher upstream pressure underneath lifts the whole diaphragm to open the main orifice. The penalty is that a servo valve needs a minimum pressure differential to work and will not open against a dead line. Either way the coil only ever has to move the small plunger, and the Manual Override provides a mechanical fallback when the circuit is dead.