It is very important to know exactly how a solenoid valve works and the different types available before kitting out your plant. In this article, I will discuss how a solenoid valve works and explain the construction of a solenoid valve.

A solenoid valve is an electromechanically controlled valve that eliminates the need for an engineer to operate the valve manually. Usually, solenoid valves are used whenever flow of media has to be controlled automatically. An increasing number of plants are taking advantage of the solenoid valve. This is due to the fact that there is a variety of different designs available, enabling the valve to be selected to suit specific applications.

Construction

A solenoid valve is a control unit that is electrically energised or de-energised to allow for the shut-off or release of flow. It is made up of two main parts: the solenoid; an electric coil with a movable ferromagnetic core in its centre, and an iron plunger that is allowed to move through the centre of the coil. When the coil is energised, the resulting magnetic field pulls the plunger to the middle of the coil. A spring is also required to return the plunger to its original position.

Operation

So, how does the solenoid valve function? When the solenoid valve’s iron plunger is in rest position it closes off a small orifice. An electrical current then runs through the coil, creating a magnetic field. The magnetic field then places force on the iron plunger, resulting in the plunger being pulled towards the centre of the coil opening the orifice. This is what in turn controls the flow, allowing for the shut-off or release of media.

Types of solenoid valves

There are three main solenoid valve technologies: direct acting, in-direct acting and forced-lift piston type. Each of these solenoid valves work in slightly different ways and are suited to different applications.

• In-direct acting solenoid valves – In-direct acting solenoid valves do require a differential pressure across the inlet and outlet to allow them to remain in their rest position. These valves are best used if pressure levels are within the parameters specified in the specific model’s datasheet and IOM instructions.

• Direct-acting solenoid valves – Direct acting solenoid valves require no differential pressure to remain in their rest position. They are robust valves that can be used in both a process line for simple isolation or for safety purposes.

• Force-lift solenoid valves – Force-lift valves are utilised in extremely high-pressure applications where neither of the above valves can handle the elevated pressure. This valve houses a larger and more powerful coil to open and close the valve’s orifice.