A Comprehensive Guide to Solenoid Valves

In this guide, we look at what solenoid valves are and how they work, plus explore the different types available.

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Throughout this comprehensive guide, we will take a close look at how solenoids work, get to know some of the various types of solenoid valves currently available, and explore what types of applications and environments they are most commonly used in.

What is a Solenoid Valve?

A solenoid valve is an electromechanically operated valve component that is used to control the rate of flow in fluid or air-powered mechanical systems. They are used in many applications for the fluid control of water, air, oil or gas.

Solenoid valves are incredibly useful to engineers and end-users due to their automatic operation. The requirement for an engineer to be physically present to operate a valve manually is removed with the use of solenoids asthey can be installed and used anywhere that gas or fluid flow needs to be automatically controlled and monitored.

What Does a Solenoid Valve Look Like?

A solenoid valve is often constructed in either poppet or spool format as a basic model option, although more specialised versions are available for tackling specific or demanding workloads, media, functions and environments. Most solenoids are modularly constructed around a fundamental arrangement of a few key components, namely:

  • Valve body - This is the main functioning part of the solenoid valve, and includes the input-output ports, valve seats, and the orifice that controls flow

  • Electrical solenoid coil - The electromagnet made from copper windings which influences the plunger motion when energised

  • Coil enclosure, housing or tube assembly - Typically a cylinder of non-ferrous metal, sealed at one end, which provides the channel within which the plunger moves in response to electromagnetic forces

Other components you might find in more advanced systems could include various arrangements of DIN terminals and connectors, for example, providing numerous options for subsequent output signals and onward controls to influence a range of behaviours further along in the system.

Solenoid Valve

What are Solenoid Valves Made of?

The vast majority of modern solenoid valves are manufactured from robust and relatively corrosion-resistant materials. Depending on the intended usage, some common solenoid valve materials might include:

Brass Solenoid Valves

Brass Solenoid Valves

Stainless Steel Solenoid Valves

Stainless Steel Solenoid Valves

Aluminium Solenoid Valves

Aluminium Solenoid Valves

Solenoid Valve Uses and Applications

You can buy solenoid valves intended for use with many different liquids and gases, including specialist configurations to cover the majority of industrial, production and laboratory environments. The wide range of types available includes products intended for applications including:

  • Hot and cold liquids

  • Compressed air

  • Steam

  • Mineral oil, natural oil and other oils (with and without additives)

  • Aqueous solutions

  • Aggressive and combustible gas

Solenoid valves are also used in a variety of everyday domestic and commercial appliances. Typical examples you might encounter on a regular basis include:

  • Heating and water flow systems

  • Lawn sprinklers and irrigation networks

  • Car washes

  • Swimming pool drainage and top-up controls

  • Medical and dental equipment

  • Refrigeration and air conditioning

  • Paintball guns, pressure pumps and other compressed air tools

  • Calibration and test stands

In terms of basic media compatibility and operating fundamentals, the options in the list below are all common variants. Many types of solenoid valve will offer specific functionality in one or more of the following areas:

  • Water solenoid valve

  • Solenoid gas valve

  • Solenoid air valve

  • Pneumatic solenoid valve

  • Hydraulic solenoid

  • High pressure solenoid valves

  • High performance/fast-acting solenoid valve

Water Solenoid Valves

Water Solenoid Valves

Solenoid Gas Valves

Solenoid Gas Valves

Solenoid Air Valves

Solenoid Air Valves

How Does a Solenoid Valve Work?

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.

Two-Way Solenoid Valves

Two-way or two-port solenoid valves are among the most common types available. In essence, they simply control one inlet port and one outlet port, and work to open or close the valve whenever they receive an electrical activation signal.

Two-way solenoid valves are therefore sometimes known simply as shut-off solenoids. They are available in both ‘normally open’ and ‘normally closed’ varieties, according to whether the application requires flow to be restricted or enabled under standard prevailing conditions.

Two-Way Solenoid Valves

Three-Way Solenoid Valves

Three-way or three-port solenoid valves have three input/output ports and two valve seals, one of which will always be open and one of which will always be closed in normal (inactive) mode.

In response to an electrical input signal, the open/closed state of these two ports is reversed, allowing for various valve operations to be controlled. Flow can thus be diverted between channels as required, in accordance with the way the port connections have been set up and connected within the larger pipeline system.

Three-Way Solenoid Valves

Direct Operated Solenoid Valves

Within the solenoid valve types outlined above, there exists a wide range of more specific operating types and functions. One of these is a direct operated solenoid valve, sometimes referred to as direct acting.

With direct operated solenoid valves, the energised solenoid acts directly on the valve sealing piston or armature. Therefore, the ability of the valve to restrict or enable flow depends on the rated power - in other words, the physical strength - of the component.

Direct Operated Solenoid Valves

Pilot Operated Solenoid Valves

With pilot operated solenoid valves, the opening or closing of the valve is powered by the energy stored in the build-up of pressurised fluid or gas.

Pilot operated solenoids can be internally or externally piloted. Internally piloted solenoid valves are used for higher pressure systems, usually found in larger pipeline setups where pressure differentials do the bulk of the work to open or close the valve. Externally piloted solenoids rely on a third-party component, such as a spring or armature, to push or pull the valve/diaphragm, working in conjunction with the typically lower pressure differentials commonly encountered in smaller pipelines.

Pilot Operated Solenoid Valves

What to Consider When Purchasing a Solenoid Valve

Many different types of solenoid valve are currently available. This is an inherent benefit of the component's great versatility - the wide range of solenoid types and functions means that it is usually possible to choose a valve that will precisely suit the role it is needed to perform and the application and environment where it will be installed.

When choosing a solenoid valve to install in a particular pipeline or flow system, the key requirements to consider will include:

  • Flow rate - A valve that is too large or overpowered for the required flow rate of a system won’t be cost-effective; similarly, a valve that is too small or underpowered for the required flow rate will not be able to provide accurate or proper actuator function

  • Media compatibility - It is important to always choose the appropriate valve for operation with water, air, steam, oil, fuel, or the particular media where it will be employed

  • Pressure - Operating pressure is among the greatest influences on the overall flow rate of a solenoid valve, so it must be balanced with the system requirements for optimal performance

  • Temperature

  • Process fitting or mounting type

Manufacturer guidelines for each of the above criteria tend to list the maximum safe rating in each case. As a result, you will need to ensure that your operating parameters fall below the specified ratings in all cases.

You will also need to potentially consider some of the solutions for solenoid valve adapters and mounts. Broadly speaking, these will often align with the type of pipeline where they will be installed, for example:

  • Compression fittings for gas or water pipes

  • Push-in or horsetail fittings for hoses

  • PVC fittings for PVC conduit

  • Various adapter types, such as sockets and reducer bushings

For each type of solenoid valve, you will also need to consider appropriate sizing and power requirements. This can be achieved by calculating a match between your precise usage needs or working conditions and the valve’s rated performance specifications in various areas. To this end, manufacturer guidelines should always be observed across each of the following areas.

For liquid solenoid valves(where liquids are broadly considered incompressible), you will need to consider:

  • Rated flow capability of the valve

  • Flow rate - often expressed as volume per minute

  • Inlet and outlet pressure

  • Pressure drop across the valve

  • Specific gravity of the fluid in question

For gas solenoid valves, where gases are considered a compressible media, there are a couple of slightly more complex considerations to take into account as well. These might include gas temperatures at various stages of the pipeline, shifting flow rates expressed in cubic feet per hour, and resulting absolute pressures at both the inlet and outlet ports.