What is a Solenoid Valve and how does it work?

Solenoid valves are essentially flow control units with the ability to restrict or enable flow. This depends on the type of valve in question and whether or not they are in a currently activated (energised) state at any given time. But how does a solenoid valve work in practice?

In a standard spool or poppet-type valve, the solenoid valve connection is direct to a plunger, pivoted armature, or another similar device, which for most models will be spring-mounted in some configuration. This plunger is located inside a hollow tube, often called the solenoid core.

When electrically energised, the wire coil wound around the outside of this core creates a magnetic field inside the tube. In turn, this influences the motion of the plunger. This then pushes or pulls the valve in a particular direction, opening or closing the flow system. The precise way in which the solenoid valve functions - either to open or close when automatically activated - will depend on the specific type and configuration of the valve and solenoid controller chosen, and thus its normal operating state.

Normally Open and Normally Closed Solenoid Valves

If a solenoid valve is normally open:

• The valve will remain open whenever the solenoid is not receiving an input signal. The rate of flow through it will remain at whatever the maximum flow rate of the conduit run or plumbing pipeline would be under normal circumstances
• This normally open type of solenoid will close the valve automatically (using the electromagnetic force generated in its coil) under an electrical input signal. In short, as the coil becomes energised in a normally open solenoid, the valve is pushed shut, and thus the rate of flow through it is automatically controlled
• As soon as the electrical input signal ceases to be sent to the coil, it will return to its normal state and position. The flow will either be restricted or enabled accordingly

The opposite of the above is true for a normally closed solenoid valve.

Complex Solenoid Valves

Some types and models of solenoid valve controllers employ additional components, including advanced circuit technologies, to offer more complex or responsive functions and features. For example, these might include the ability to manage proportional flow or pressure control, achieved through coil sensitivity to a broad range of input signal strengths.

It’s worth noting that, in fluid dynamics terms, normally open (i.e. flow-enabled) valves typically imply the opposite meaning to normally open gates in electronic systems.