Solenoid valves are essentially flow control units with the ability to either restrict or enable flow, depending on the type of valve in question and whether or not they are in a currently activated (energised) state at any given time. But exactly how does a solenoid valve work in practice?
In a standard ‘spool’ or ‘poppet’-type solenoid valve, the valve itself is connected directly 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 referred to as 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, which then pushes or pulls the valve in a particular direction, with the end result being the opening or closing of the flow system. The precise way in which the solenoid functions - either to open or to close a valve when automatically activated - will depend on the specific type and configuration of valve and solenoid controller chosen, and thus its ‘normal’ operating state.
'Normally Open' and 'Normally Closed' Solenoid Valves
If a particular solenoid valve is of the ‘normally open’ type:
- 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 cause the valve to be closed 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, and flow will either be restricted or enabled again 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 broader 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 electronics systems.