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How does a solenoid valve work?

Solenoid valves use electromagnets to open and close a valve, controlling the flow of water or another fluid through the valve.

At their most basic, solenoid valves operate by passing current through a coil of wire. This induces a magnetic field that can be used to move an armature, opening or closing the valve.

However, there are a few different types of solenoid valves, all of which use this same scientific principle of electromagnetic induction to operate.

Direct solenoid valves

Direct solenoid valves have a seal connected directly to the core of the solenoid. When no current is present, the seal is usually in the closed state, blocking the flow of the fluid.

When a current passes through the solenoid, a magnetic field is generated, pulling the core of the solenoid away from the sealed position and allowing the fluid to flow.

Direct solenoid valves can be one-way, with a simple orifice in the seat to allow fluid flow, or two-way with an inlet and outlet port.

Some also have three-way operation, so that in the default state one port is open and one is closed, and in the energised state the configuration is reversed.

Internally piloted solenoid valves

Internally piloted solenoid valves are used in applications when the magnetic force of the coil might not be enough to overcome the pressure force of the fluid flow.

Instead, in an internally piloted solenoid valve, the configuration is such that the fluid pressure differential is minimised or used in such a way as to support, rather than resist, the opening or closing of the valve.

Again there are different configurations, including one-way, two-way and multi-way internally piloted solenoid valves, and the orientation during installation can affect the logical operation of the valve in use too.

Externally piloted solenoid valves

Finally, externally piloted solenoid valves use an independent medium – rather than the pressure of the primary fluid – to assist when actuating the valve.

These can include springs in different positions to achieve a normally open or normally closed valve, to suit the best default state for the specific application.

Choosing the correct type of solenoid valve can help to ensure reliable operation, especially in applications with large fluid flow where a direct solenoid valve might struggle to overcome the fluid pressure.