What are Solenoid Valve and How Do They Work?

When the flow or direction of fluid in a system has to be controlled, a regulating valve is used. The valve can be manual or automatic.

Automatic valves are more common, with the electronically operated solenoid valve being one of the most popular.

This article takes you through the workings of a solenoid valve and its application in the industrial, engineering, and manufacturing systems.

We will also look at the types of solenoid valves out there and the different materials used to make them.

Before that, something about what the solenoid valve means.

What’s a Solenoid Valve?

Also known as an electric valve, electromagnetic valve, or electrovalve, a solenoid valve is an electromechanical device that uses an electric current to operate a valve.

You can easily recognize a solenoid valve by its distinctive look.

It’s usually the valve on some gas or liquid lines with a small block on top and wires coming out of it.

Solenoid valves can be used in many different applications where gas or liquid lines are involved. These can be in the automotive industry, manufacturing industry such as beverage factories, oil plants, household appliances like dishwashers, and many more.

Solenoid valves come in a broad range of sizes, shapes, strengths, designs, working mechanisms, materials, and others.

Based on these variations, valve choice depends on several factors, such as capacity, line pressure, internal design, type of fluid, among others. 

Solenoid Valve Working Principle

Solenoid valves may employ different methods and mechanisms to stop, allow, or restrict the flow of liquid or gas.

However, their electromechanical actuation remains the same.

A typical solenoid valve comprises these two main parts: an electromagnet assembly or solenoid and the valve body with the orifice and ports. The solenoid consists of wire coil, plunger, sleeve assembly, and sealing material which can be rubber or metal.

When an electric current flows through the solenoid assembly, it energizes the coil and creates a magnetic field. This causes the plunger to either move up or down. The movement opens or closes the valve, which can be partially or fully depending on the required action.

A solenoid valve can be one of these types: normally open solenoid valve (NO) or normally closed solenoid valve (NC).

A normally open solenoid valve maintains an open line where fluid is free to flow through. It only closes when an electric current is applied.

A normally closed solenoid valve keeps the valve closed and only opens when the solenoid is energized to work the plunger. In this type of valve, the flow of liquid or gas is normally restricted when there is no current flowing in the coil.

Solenoid Valve Materials

With the wide range of media passing through a solenoid valve, it’s highly necessary that the materials used to make it be the right type.

If the media is a hot liquid or gas, the solenoid and valve materials should be able to withstand the high temperatures.

If the media is corrosive, the valve should stand up to that.

It’s the reason why these valves come in different materials, which are often different for the valve and the solenoid assembly.

Let’s now look at the common materials used to make solenoid valves.

PVC or PolyVinylChloride Solenoid Valve

With impressive chemical properties, PVC solenoid valves can be used with fluids that contain salts and organic solvents. The material is also resistant to a wide range of acids and alkalis.

A disadvantage of PVC is that it requires lower pressure and temperature ratings when compared to other materials like brass and steel. It also doesn’t stand up to chlorinated hydrocarbons well.

Nylon or Polyamide Solenoid Valve

In addition to being less costly, nylon has one of the best chemical and mechanical characteristics. The material resists salts, solvents, oils, and hydrocarbons.

One of the drawbacks of nylon for solenoid valves is that the material cannot resist the corrosive action of some acids and bases. Its temperature and pressure ratings are also lower than that of metal materials.

Brass Solenoid Valve

With high pressure and temperature ratings, brass makes a good material for solenoid valves to control different media. A brass solenoid valve can be used in water, compressed air, and oil lines provided there are no corrosive substances.

Among the disadvantages of brass is that the material cannot withstand corrosive media such as acids, saltwater, chlorides, and distilled water. However, a special type of brass that resists corrosion is often used for harsh media.

Nickel-plated brass is one such material. It withstands salts, nitrogen and sulfur compounds, weak acids, hydrogen sulphide, oxygen, and carbon dioxide. Nickel-plated brass also possesses higher temperature and pressure ratings than normal brass.

Although the advantages of Nickel-plated brass are many, the material has its downsides. Nickel-plated brass is prone to scratches. If that happens, the layer underneath becomes exposed and the valve may start to corrode. 

Stainless Steel Solenoid Valve

A stainless steel solenoid valve can be made from grade 304 or 316 stainless steel. The material’s main strengths lie in its ability to withstand high temperatures and pressures.

This makes stainless steel solenoid valves better than plastic solenoid valves in high-pressure lines that carry very hot fluids.

Stainless steel also resists wear, making it a durable material for a solenoid valve. The chemical properties of the material are also impressive and it can be used with a wide range of media without the risk of corrosion.

When it comes to general appearance and maintenance needs, a stainless solenoid valve can be a big advantage. It resists stains, which makes valves made from the material one of the most used in the food industry.

A downside of stainless steel is the poor resistance to the corrosive action of hydrochloric acid, bromine, and chlorides. Stainless steel solenoid valves can be made from different grades of steel metal. It depends on the requirements. Solenoid valves can also be made from bronze or aluminum. However, these materials are not common.

Most of these valves will be PVC, nylon, brass, nickel-plated brass, and stainless steel. The seals used in solenoid valves can be rubber or metal. In most applications, rubber is the most common material, with some employing stainless steel seals. Each material has its up and downsides and the best choice depends on the pressure and temperature levels involved.

Solenoid Valve Vs. Pneumatic Valve

In many liquid and gas systems, electric and air actuated valves are used. The most popular of these are the solenoid and pneumatic valves.

The type used depends on the required functions, which can be different across different applications. The kind of fluid and the environment also play a role in determining the type of valve to use.

To understand what these requirements are, let’s look at the advantages of each valve type.

Solenoid valves have the highest closing speeds, with some achieving up to 10m/s. They are also precise and highly accurate, which makes then suitable in the systems to dose or mix fluids.

Another advantage of solenoid valves is their almost noiseless operation. This is why they’re the most preferred type of valve in environments where sounds are unwanted.

You will find solenoid valves in the manufacturing plants, used in automation systems. In the automotive industry, different solenoid valve types can be found in dump trucks, excavators, and a majority of forklifts.

Road vehicles also utilize solenoid valves in a variety of functions such as fuel regulation to control speed, oil flow control, and the HVAC system. Micro solenoids valves are also utilized in robots for their precision and high closing speeds.

Pneumatic regulatory valves produce closing forces and pressures that are much higher than those of solenoid valve types. It’s not uncommon to attain up to 250 PSI and 40 000 lb with pneumatic valve types, which makes them the most suitable for high-pressure lines or large scale circuits.

Pneumatic valves are also low-cost and a good choice when many valves are needed in a system. They are also upgradable from one size to another. Because pneumatic valves do not use electricity, they suit conditions where sparks could cause a fire.

Pneumatic valves can found in internal combustion engines regulating the flow of fluids, in ventilation systems, and different types of pumps. Just like the solenoid valve, the size of pneumatic valve depends on the closing forces required.

Which valve type is better? Solenoid or Pneumatic

In comparison, solenoid valves are faster, more accurate, and less noisy than pneumatic types. In situations that require a fast-acting solenoid valve, the magnetic valve is the most appropriate.

But the electric control valves have their downsides. They’re more expensive and less powerful, which can be disadvantage in some situations. Solenoid valves are also unsuitable to use in environments that contain ignitable materials.

Pneumatic or air valves, despite being relatively slow and noisy, are more powerful and cheaper. You can use them with flammable media without safety issues, which makes them the only option in some applications. You can also use them to control a wide range of lines due to their flexibility when it comes to upgrading.

Conclusion

Solenoid valves control the flow of fluids using an electromagnetic actuator.

They’re fast and accurate, which explains their wide use in applications that require precision.

Simple to make, solenoid valves are also the most common of all valve types. They can be miniaturized and the reason for their popularity in many fluid systems today.

The valves exist as different types with each suiting specific requirements. The type to use depends on the kind of of fluid, its condition, and flow rate, among other factors.