The Complete Guide 2021

A solenoid valve is a very useful piece of machinery that is utilized in a wide range of applications, from simple home appliances to complicated industrial and automobile machinery. As an important component in the industries, a solenoid valve’s purpose is mainly to control machines, measure the flow of liquids and gases, as well as mix and restrict air and liquid flow. Although a solenoid valve is just a simple machine, with a simple mechanism, it is used extensively to create effective processes in both hydraulic and pneumatic fluid power systems. Hence, understanding the basics of a solenoid valve will utterly provide you with the right guidance on how to choose the right valve for your application.  Moreover, before you can decide on what type of solenoid valve you ought to purchase, it is wise to gain sufficient information about the application. Likewise, you need to conduct careful research so that you can obtain the right valve that matches your requirement.

Understanding The Fundamentals Of Solenoid Valve

Apart from a solenoid valve’s opening and closing functions, it operates to enhance safety measures in its application. According to Control Global, solenoid valves are used to vent a valve actuator to move the valve in a safe state. (1) This electromechanical device is designed to help secure and fasten safety interlock systems. Moreover, it has a highly reliable sensor that is electrically activated to safely control the passage of fluid either remotely or automated.  Fluids that pass through tubing or piping are not limited to gas and water but also refers to steam, refrigerant, oil, and natural gas.

  • Solenoid

The solenoid is the coil made of cylindrical wire that generates the magnetic field when energised by an electric current. 

  • Valve 

The valve is the control device that manipulates the direction of the fluid flow, either by closing or opening the pathway.

  • Valve Body

This component houses the ports, seats, and orifice and allows fluid movement.

  • Plunger

The plunger is the moving part of the solenoid that is made of an electromagnetic coil. The plunger moves up or down when energised or de-energised.

  • Plunger Spring

The spring serves as a mechanical return, holding the plunger in a fixed position when energised, and then returns the plunger in its original position.

  • Seat Seal

The seat seal is located in the plunger and closes the valve orifice.

Solenoid Valves Working Principles

The solenoid valve works primarily using a two value numbering system, 2/2, 3/2, or 4/2. The first value of the numbers indicate the number of ports, and the second value indicates the number of valve positions available. Hence, in this representation, a 2/2 would mean that the solenoid valve contains 2 ports and 2 positions. Likewise, a 3/2 solenoid valve would mean that it contains 3 ports and 2 positions or switching states.

Generally speaking, the solenoid functions following the principle of electromagnetism. When an electrical current energises the solenoid, a magnetic field is created, thereby, causing the plunger to interact with the magnetic field. This results in the movement of the plunger causing the valve to open or close.

Types of Solenoid Valves

Solenoid valves are categorised into five types and are basically utilized in industrial applications. Moreover, all solenoids convert electrical energy to mechanical energy, thereby, capacitating machines to run with high functionality.

  • Direct Acting Solenoid Valve

A direct-acting solenoid valve is also known as a zero-rated solenoid valve that incorporates the use of a coil to magnetically open the valve. This action forces the valve’s shaft to shift, thereby,  allowing the flow of liquids. When there is no current applied to the coil, the spring component of the valve holds the plunger onto the valve seat. However,  as the coil generates electricity, it raises the plunger and opens the channel for liquid flow. Hence, the valve is opened when the plunger is lifted from the valve seat through the magnetic force produced when the solenoid is energised. The advantage of using this type of solenoid is its ability to function in negative pressure circuits, and since they have smaller body sizes, they tend to function in low flow or high-pressure applications. 

  • Two-Way Solenoid Valves

This type of solenoid valve consists of two ports, an inlet and an outlet to permit or shut the flow of fluid. This is normally seen in some industries where the use of liquid and gas are essential to perform operations. Moreover, the main purpose of a two-way solenoid valve is to automatically open and close the valves to start or stop the flow of liquid or gas as needed. The incorporation of these valves into the equipment permits a safe and efficient operation. With the use of a plunger, a solenoid valve allows the flow of the liquid without any leaks. Likewise, when the machine is not in use, the solenoid valve is fittingly fastened to the machine so that it prevents leakage. Hence, every industrial operation highly depends on solenoid valves to allow effective and systematic processes. To simplify its function, a normally closed solenoid valve that is not powered indicates that the plunger is down, resulting in an effectively sealed valve and preventing the flow of liquid or gas. On the other hand, a normally closed solenoid valve that is powered up or electrically energised causes the plunger to rise, and once again, unseals the valve, resulting in a direct flow of liquid or gas.

  • Pilot-Operated Solenoid Valve

In comparison to the direct-acting solenoid valve that directly uses the power supply from the electromagnet to open and close the valve, the pilot-operated solenoid valve combines both the power from the electromagnet and the pressure of a fluid to open and close the valve. The advantage of using a pilot-operated solenoid valve is that it only requires a small amount of energy to operate at high pressure and temperature ranges. However, a full power force must be required in order for the valve to remain in an open state. Although this pilot-operated solenoid valve works at a slower rate, still,  a lot of industries take advantage of its functionality. The pilot-operated solenoid valve is primarily used to facilitate the flow of liquid and gaseous matter such as compressed air, water and hydraulic oils. Since they don’t require much energy and can stand sufficient pressure difference, pilot-operated solenoid valves are best applied in irrigation systems and car wash equipment.

  • Three-Way Solenoid Valve

The three-way solenoid valve is plainly similar to the two-way solenoid valve and is also functional when utilised in pneumatic and electric actuators. The difference between the two is that the three-way valve uses an additional port. According to Solenoid Solutions, there are three different types of three-way solenoid valves, a three-way normally open solenoid valve, a three-way normally closed solenoid valve, and a three-way directional solenoid valve. (2)  All these three-way solenoid valves are composed of three important ports, the cavity port, the orifice port and the body port. Likewise, they have two orifices, the body orifice and the stop orifice of which one is always open. Because of the two orifice ports, the three-way solenoid valves allow two paths of flow.  

When the power is turned off in the three-way normally open solenoid valve, the plunger is in a raised position, the stop orifice is closed, and the body orifice is in an open state, thereby, allowing fluid to flow through the valve into the cavity port. On the other hand, when the power energises the coil, the plunger is in a down position, closing the body orifice and opening up the stop orifice to allow the flow of liquid from the cavity port and into the stop orifice port.

When the power is turned off In the three-way normally closed solenoid valve, the plunger is in a down position, closing the body orifice, and opening up the stop office to allow the flow of media through the body of the valve and into the stop orifice port. However, when the power energises the coil, the plunger is lifted and seals off the stop orifice, opening up the body orifice. This mechanism facilitates the flow of the liquid through the body of the solenoid valve, and into the stop orifice port.

Finally, the three-way directional solenoid valve has a different mechanism from the normally open and normally closed solenoid valves. This is because when the power energises the coil, the valve raises or lowers the plunger. A raised plunger will close the stop orifice at the same time, opening the body orifice. This allows the flow of the liquid through the body of the valve.

  • Four-Way Solenoid Valve

This type of solenoid valve is composed of four ports, two pressure inlets and two exhaust outlets. To make this valve work, electric power and air pressure are applied. However, air pressure is the more common option for its power source. Although there are many designs for this kind of solenoid valve, their functions are most beneficial. Many industries benefit from the four-way solenoid valve because the flow can be facilitated through multiple directions just using a single device.  This functionality is mainly attributed to the solenoid’s capacity to carry four or more ports. Thus, individuals who have limited connections for their control system will likely choose this kind of solenoid valve.

One type of four-way solenoid valve is the stepper valve which is utilized to run tasks that need sequential positioning, without the need to go back to the original position. This mechanism usually applies when you operate lawn sprinkling, water softener regeneration, and pool chemical treatment. 

Considering the many types of solenoid valves, and if you are planning to purchase one, it is wise to make a careful research on what kind of solenoid is required by your system or machine. At the same time, you also need to examine the type of liquid that will be used in your operation. Other than that, it is also required to determine what material will be used for the seals. In this way, your system will not fail.

Additional Types Of Solenoid Valve

While there are basic types of solenoids that either operate as direct or indirect, there are also additional types of solenoid valves that are equally important too.

  • Latching Solenoid Valve

The basic mechanism of a latching solenoid valve is the utilization of a latching solenoid that firmly holds the valve in a given position, either close or open even in the absence of power. To make this happen, a permanent magnet is installed to hold the plunger after the electrical signal energises the solenoid. With the attachment of the magnet, the valve is able to hold an open or close state without the assistance of electrical flow in the solenoid. Thus, the plunger remains in the same position. A lot of applications depend on the ability of the latching solenoid valve to function even with minimal power or none at all. Power consumption is highly reduced, making it suitable for battery-operated applications. Unfortunately, the latching solenoid valve may not function properly in applications that produce high levels of vibrations or shock as this can cause the plunger to shift or break free from the magnet’s force. When this occurs, the device may be unlatched causing the valve to fail tremendously. 

  • Rotary Solenoid Valve

This type of solenoid valve converts the electrical energy from the solenoid coil causing it to produce a rotational motion. This conversion can be done in several ways, and one is utilizing the use of ball bearings.  When electrical energy passes through the valve, the plunger begins to rotate due to the movement of the ball bearings in an angular displacement.  Its uses extend to diverse applications in security, medicine and industry. There are advantages of using a rotary solenoid valve. One is that it uses minimal power to create movement in the valve.  Rotary solenoids are also cheap, and yet, provide the necessary rotation with high dynamics.

The Different Functions Of A Solenoid Valve 

Solenoid valves are extremely important devices used to execute a wide range of applications from simple machines to complicated ones. Moreover, these devices are fast, accurate and noiseless.

Solenoids in the Manufacturing Sector

Solenoids are utilized in different industrial machines to mix, restrict or allow the flow of media such as oil, liquid and air. In the case of manufacturing beverages, solenoid valves permit, restrict and measure the flow of the beverages that must be placed into the battles. Moreover, several processing industries depend on solenoid valves not only to dispense food but also to preserve them. For instance, solenoid valves preserve wine, filter water, dispense food condiments, among others.

Solenoids in Agriculture

Solenoids can be highly useful in agricultural machines, especially in an irrigation system such as automatic sprinkles. They are also present in automated farm machines to measure substances. Generally, in an irrigation system, a solenoid valve controls the flow of water so that the sprinkler can equally dispense water. In other agricultural machines, solenoid valves are also used to mix and permit the flow of chemicals. 

Motor Vehicle System

Another crucial function of a solenoid valve is to control the flow of oil fluids such as brake oil and fuel. While it functions to permit fluid, it can also control the flow of fluid instead of shutting it completely. This is evident in reducing vehicle speed by limiting the flow of fuel in the engine. In addition to this,  solenoid valves are also configured to control the flow of the diesel engine fluid coolant system, as well as provide functions for water-pump controls, oil pump controls, and transmission fluid controls. New innovations of solenoids are also incorporated into the built-in safety features of vehicles due to the valve’s ability to withstand extreme temperatures, high pressure and high speed.

Home Heating Systems And Appliances

Even in your homes, your heating and cooling systems are maximising the functions of solenoid valves to distribute heat into the showers, faucets,  and other installations. Solenoid valves are automatically allowing and restricting the flow of hot or cold water and air from your machines. Moreover, you also benefit from a solenoid valve in your refrigeration system and air conditioning system. It basically prevents the flow of refrigerants.

Car Washing Systems

Car washing equipment incorporates the use of solenoid valves to mix water and cleaning material in high-pressure mode to clean up motor vehicles. Moreover, the high-pressure water is also mixed with wax for thorough cleaning. During the cleaning cycle, the solenoid valves permit the flow of cold and hot water into the circuit. Once this is done, more solenoid valves function to control the flow of foam, wax, and detergent to mix with water.  To prevent corrosion of the valves during the cleaning process, manufacturers use nickel-plated brass.

Air Compressor Units

Solenoid valves are used in air compressor units to take in filtered air, send it to the refrigerator, and finally, keep it under pressure inside the tank. The filtered air remains in the tank until a  requested pressure level is reached. As the pressure level is reached, the motor is then turned off.  However, to prevent damage to the compressor due to pressure, the power is switched off causing the solenoid valve to open.While the solenoid valve makes it possible to compress the air inside the tank, it also allows the air to be released.

Commercial Appliances

Solenoid valves are also useful in commercial appliances such as hot and cold drink dispensers. These machines usually control the flow of coffee, tea, and other beverages. Furthermore, these machines are also seen in commercial buildings and offices. The solenoid valves are placed in sequencing positions to open and close the valves, causing the flow of liquids.

Water Metering Devices

The food industries are also benefiting from solenoid valves to regulate the amount of water dispensed. Moreover, the solenoid valves also measure the water as it mixes with other mixtures. 

In other industries, such as the farm industry, the metering devices do not measure water, but it is also designed as feeding equipment for cattle. Corn is mixed with water and distributed to the network through the pump.

Installation of Natural Gas

Aside from industrial gas systems, solenoid valves are also used in a home gas system. The use of natural gas in the home becomes easy because of the solenoid’s closing and opening mechanism. It also controls the flow of the gas and directs it to the heating or cooling system of the home. 

Floor Washing Machine

This device uses the ability of the solenoid valve to dispense water and cleaning agents at the same time with the right measurement.

Tap Water Sanitation

Solenoid valves are also used for tap water sanitation in some places where it is deemed necessary. In this process, the valves are mixed with cold and hot water before it can be transported into the faucets. The solenoid valves simultaneously open and close to let the water in. Furthermore, it involves the installation of a pilot operated solenoid valve due to the presence of high water pressure.


The highly functional solenoid valves have become an integral part of everyday processes, resulting in a fast, safe and effective delivery. In the home, the solenoid valves are used to operate machines and devices to give our homes safety and protection, as well as comfort. Because of its locking mechanism, solenoids are included in door locks. Medically speaking, solenoid valves are installed in machines and devices to produce high accuracy data. This is because the health care institution is dealing with human life, and requires adherence to strict standards. Furthermore, a solenoid valve is an essential part in a dialysis machine. In this mechanism, two solenoids are tasked to control the flow of blood during the dialysis process. While the two solenoids controls the blood flow, another set of solenoids in the dosing machine controls the flow of medicine that goes into the bloodstream. Because solenoids have different uses, it is important to be careful when buying them. For safety concerns, every buyer should look for high quality solenoid products.

References: Control Global, Application fundamentals of safety solenoids: Solenoid Solutions, Different Types of 3-Way Valves: