Learn solenoid valve and its working principle. How its coil energized and work in lock,valve.Learn electro magnetic.

What is solenoid in Physics?


When we hear the word “solenoid”; our minds may conjure images of complicated mechanism and complex electrical systems. However, fundamentally, a solenoid is a simple yet remarkable device that plays a crucial role in various aspects of modern technology.

Understanding Solenoids

The basic structure of a solenoid is a coil of wire wound into a helical shape, much like a tightly wound spring. The function of the wire is primarily dependent on the magnetic field that is produced when an electric current passes through it. A uniform magnetic field is produced along the axis of the solenoid as a result of the interaction between the magnetic fields produced by each loop of the coil.

Working Principles of Solenoid

Ampere’s law, which states that a closed current loop generates a magnetic field proportional to the current flowing through the loop, is the fundamental idea guiding how a solenoid operates. In this instance, the wire coil acts as the closed loop, and as additional loops are added, the magnetic field becomes stronger and produces a stronger magnetic effect.

A solenoid’s capacity to concentrate the magnetic field within its core is one of its essential characteristics. This is caused by the coil’s loops being so close together; as a result, the solenoid’s centre experiences the majority of the magnetic flux. Because of this quality, solenoids are incredibly beneficial in a range of applications.

The Formula of Solenoid:

The magnetic field produced by the solenoid can be determined using the following formula:

B=(μo x N x I)/L


B is the magnetic field strength at the centre of the solenoid,

Permittivity of free space (μo): This is the fundamental constant of electromagnetism, approximately equal to .

It relates the strength of the magnetic field to the current flowing through the solenoid and the number of turns of the wire.

Current (I): The current (measured in amperes (A)) through the coil plays a key role in determining the strength of the magnetic field.

Number of turns (N): The total number of turns in the magnetic coil directly affects the strength of the magnetic field. The more turns, the stronger the magnetic field.

Length (L): refers to the length of the electromagnet in meters (m). The strength of the magnetic field tends to be higher at points closer to the centre of the solenoid and decreases as it moves away from it.

Radius (r): Specifies the radius of the solenoid in meters (m), which also affects the strength of the magnetic field.

Breaking down the formula

 It shows that the magnetic field strength is directly proportional to these factors. The higher the permeability, and more turns, and the current, the stronger the magnetic field.

L: The length of the solenoid appears in the denominator. This means that as the length increases, the magnetic field strength decreases, and vice versa.


A solenoid coil is a dense cylindrical coil wound with an insulated wire.

How magnetic fields are generated by Solenoid coils?

When an electric current passes through the windings of a solenoid coil, it gives rise to a magnetic field. This magnetic field exhibits a distinct pattern, with its intensity and orientation being influenced by various solenoid characteristics- which includes the number of turns in the coil; the current strength; and the physical dimensions of the coil.

The solenoid coil’s beauty lies in its capacity to focus this magnetic field within its core, producing a potent and concentrated magnetic force there. Solenoids are essential in applications that call for precise and controlled magnetic interactions because of this property.

Applications of Solenoid Coils:

Solenoid coils have secured their place in countless applications across diverse fields due to their versatility and reliability. Let’s take a look at some of the key areas where these coils play an important role:

Electromechanical Device:

One of the most prevalent uses of solenoid coils can be found in electro-mechanical devices.

For example- Solenoids serve as the driving force behind electro-magnetic locks, employing their coils to create a robust magnetic field that ensures doors are securely locked. Moreover, solenoids are utilized in valves, relays, actuators, and switches, harnessing the power of magnetism to facilitate mechanical movement.

Medical Equipment:

In the medical field, solenoid coils are used in magnetic resonance imaging (MRI) machines. These advanced imaging devices uses powerful solenoid magnets to generate the magnetic fields, needed to produce detailed cross-sectional images of the human body.

Telecommunications and electronics:

In telecommunications and electronics, solenoid coils are an integral part of loudspeakers, sound signals and various sensing devices. The magnetic fields created by these coils are used to convert electrical signals into sound waves and vice versa.

Industrial automation:

In industrial automation, it plays a critical role in controlling fluid flow in hydraulic and pneumatic systems. Their ability to provide accurate and fast actuation makes them valuable in processes that require fast response times.

Challenges and future prospects:

Although electromagnetic coils have come a long way, some problems still exist. Heat dissipation remains a critical issue, especially in high-power applications. Scientists are actively researching cooling methods and heat-resistant materials to overcome this challenge.

As we cast our gaze towards the horizon, the future of solenoid coil technology appears exceedingly promising. By integrating the prowess of artificial intelligence and state-of-the-art machine learning algorithms, the efficiency and overall performance of solenoid coils can be further elevated. This remarkable fusion has the potential to revolutionize the landscape of solenoid coils, ushering in a new era of advancement and innovation.

Moreover, the advent of additive manufacturing, commonly known as 3D printing, emerges as a game-changing development that holds immense potential for transforming the production process. This groundbreaking technique allows for the creation of intricate and tailor-made designs for coils, propelling the industry towards unparalleled levels of complexity and customization.


Solenoids and Magnetic Fields: An Introduction

A tightly wound coil of wire in the form of a cylinder makes up a solenoid. They are simple yet essential electromechanical devices that work on electromagnetism principles. The term electromagnetism is a relation between electricity and magnetism; where an electric current flowing through a conductor creates a magnetic field around it. This magnetic field has a significant effect on the behavior of nearby magnetic materials and other conductors.

The Structure of Solenoid:

The structure of the solenoid is relatively simple. It usually consists of a cylindrical core, which is usually made of a ferromagnetic material (such as iron or steel) because it increases magnetism. Around this core, the wire is wound in a spiral, forming a coil. Wires are usually made of conductive materials such as copper. To prevent short circuits, wires are often insulated with a non-conductive material such as enamel. The coils can be wound tightly or loosely depending on the intended application and the strength of the magnetic field required. A tightly wound coil with more turns will produce a stronger magnetic field than a loose coil with fewer turns.

 Magnetic field direction:

When current flows through the solenoid coil, a magnetic field is created around it. The magnetic field lines run parallel to the axis of the solenoid, creating a uniform magnetic field inside the coil. This means that the magnetic field strength is same at all points of the solenoid, thus resulting in a consistent magnetic force.

Inside the solenoid, the magnetic field lines line up in the same direction, effectively forming a north pole at one end of the solenoid and a south pole at the other. So the solenoid behaves like a magnet with a North and South Pole.

The Biot-Savart Rule:

Biot-Savart’s Law is a fundamental principle of electromagnetism that describes the relationship between electric current and magnetic field. This Law can be used to figure out the strength of the magnetic field (B) at a specific location inside the coil of a solenoid.

According to the law, the solenoid’s number of turns (N) and the product of the current (I) flowing through the coil determine the magnetic field’s strength. Additionally, it is inversely proportional to r, the distance from the coil’s centre. A constant that appears in the equation, i.e. the permeability of free space ( ), describes how easily a magnetic field can pass through a vacuum. The Biot-Savart Law is a mathematical formula that describes the magnetic field of a solenoid.

B = ( * N * I) / L.

Where N = the number of turns in the solenoid,

I is the current flowing through the coil, and

L is the length of the solenoid,

B = strength of the magnetic field at the point,

 (mu naught) is the permeability of free space (roughly  * T m/A), and permeability of free space is determined by the permeability of space.

The magnetic field strength can be calculated quantitatively at any point inside the solenoid using this formula.

Magnetic Field Concentration :

Magnetic field concentration is the concentration of magnetic energy in the coil of a solenoid. It is strongest at the centre of the Solenoid (directly along its axis) and weakens as you move away from the centre.

The magnetic field within Solenoid is uniform and is a great tool for producing a controlled and focused magnetic force. However, the magnetic field outside it becomes much weaker and less uniform. The lines of the magnetic field increase and decrease in strength as you get further away from the Solenoid, and hence the magnetic effect of the magnet is mainly restricted to its immediate environment.


Solenoids are essentially coils of wire wound around a cylindrical core. When an electrical current passes through the coil, it induces a magnetic field along its axis. This field, which acts like a mysterious force, has a wide range of applications and has become an essential part of modern life.

Electromagnetic Locks:

 Imagine a secure door that remains firmly closed until an electric current flow through a solenoid. The magnetic field it generates pulls a metal plate strongly, effectively locking the door. The door can be opened easily once the current stops. This technology is widely used in accessing control systems, providing secure and convenient entrances.

Automotive Starter Motors:

When you start your car, a solenoid in the starter motor engages the engine’s flywheel. This action initiates the engine’s cranking. The magnetic field produced by the solenoid’s current enables this precise engagement, starting your car’s internal combustion process.

Medical Devices:

Solenoid plays an important role in medical devices. For instance, in MRI machines, strong solenoids generate a powerful, even magnetic field that allows for precise imaging of the internal structures of the body.

Industrial Automation:

Solenoids acts as a valves that regulate the flow of liquid or gas in industrial processes, such as production lines or complex chemical plants.

Printing and Packaging:

Have you ever thought about how printers or packaging machines manage the flow of ink or glue? It is done by Solenoids, which controls the flow of materials and ensures accurate and consistent results for printing and packaging operations.

Robotics and Actuators:

In robotics, solenoids are like actuators – they take electrical energy and turn it into mechanical movement, so robots can do things like open and close grippers or move their arms like humans.

Musical Instruments:

Solenoids are a key part of all musical instruments, from electric guitars to electric pianos. They help musicians to create different melodies and harmonies by striking or plucking strings on electric pianos.

Electric door locks:

Electric door locks are a popular choice for modern buildings due to their security and convenience. Electric door locks are equipped with solenoids that control the locking and unlocking systems, allowing for quick access via a simple electrical signal.

Railway applications:

The railway industry has a wide range of applications, from locomotive functions, to rolling stock, track, signals, power distribution, to general maintenance and building applications.

For passenger turn-styles controlled by tickets, the solenoids used are standard variant, bi-stable, long-life solenoids.

For passenger car doors, the safety interlocks are solenoids operated by a remote solenoid remote mechanism.

In summary, Solenoid uses are not limited to these examples. Solenoids and their magnetic fields allow controlled, precise motion through electromagnetic principles.  Many industries use solenoids to increase efficiency, ease of use, and innovation.


A solenoid valve is a valve that is controlled by electricity. This valve contains a piece called a solenoid, which is basically an electric coil with a piece of iron in the middle that can move (we will call it a “plunger”). When the valve is not functioning, the plunger blocks a tiny hole.

When an electric current passes through the coil, it creates a magnetic force around the coil, which causes the plunger to push upwards. This forces the plunger to open the small hole that was previously closed. This simple trick allows us to regulate when the valve will let things pass and when it will stop them.

When we want something to pass through the valve, we simply send the electric current into the coil. The magnetic force will lift the plunger up, opening the small hole. If we want to stop, we turn the electric current off, causing the plunger to go back down, closing the hole once again.

This simple trick makes solenoids open and close, and allows the flow of liquids or gases to be regulated.

Working Principle of Solenoid Valve:

The function of a solenoid valve is based on the fundamental principles of electromagnetism. Let’s examine them one by one:


The interaction of magnetic fields and electric currents is known as electromagnetism. A wire develops a magnetic field around it when an electric current flows through it. This phenomenon is the basis for the operation of the solenoid valve.

Wire Coil:

A solenoid valve is made up of a wire coil that is typically enclosed in a cylindrical shell. When an electric current flows through this coil, it acts as a magnet. It is made up of a number of loops that control how much electricity flows through the valve.

Magnetic field generation:

As the electric current passes through a coil, it creates a magnetic field inside and around the coil. In this way, it creates magnetic field around it.

Metal Core:

Most solenoids have a metal core inside the coil. They are usually made up of metals such as iron or steel, which improves the magnetic properties of solenoids. The magnetic flux that results from the current flowing through the coil concentrates within the metal core. This concentrates the magnetic field in the vicinity of the metal core.

Magnetic induction:

The metal core increases the magnetic induction in the coil.  Thus, it increases the ability of solenoids to attract and control specific materials, for example, the flow of liquids or gases.

Flow control:

The enhanced magnetic field of the core has a direct flow control function. The solenoids have a valve mechanism called a plunger. The plunger is usually made of a magnetized material. When an electric current is applied to the solenoids coil, the magnetic fields pull the plunger towards the core.

Opening and Closing:

When the plunger is pulled towards the core, it creates a path for the liquid or gas to pass through the valve. But as soon as the electric current is stopped, the magnetic field weakens and the plunger moves back to its original position, thus blocking the pathway and stopping the flow.

Polarity and interaction:

An activated solenoid is a magnet with two poles – a positive pole and a negative pole. The positive and negative poles of the solenoid interact with the surrounding magnetic materials. Depending on the solenoid’s configuration, it can attract or repel magnetic objects.

Adjustable Strength:

The solenoid’s magnetic field strength can be adjusted by varying the flow of current through the coil. The magnetic field becomes stronger when the current is higher. When the current is lower, the magnetic field becomes weaker.

The magnetic field strength can also be affected by the coil’s design, such as the number of loops or the core material present in the coil.

Basically, solenoid uses electromagnetism to regulate the flow of liquids or gases. Basically, it is a system made up of a magnet, coil, magnetic field, metal core, and plunger. You can adjust the electrical current to control the fluid flow. This principle is used in everything from industrial machines to everyday appliances that need precise fluid control.

Different Types of Soln Valves with Examples:

Solenoids are a type of valve that can be used to regulate the flow of liquids or gases. Depending on its intended use and the industry in which it is employed, it is available in a variety of sizes and shapes. To control the flow of liquids, they essentially use electromagnets.

Two Ways (2 Ways) Solenoid Valves:

The most popular kind of solenoids is 2-way solenoids. Both an inlet port and an outlet port are present. They are employed to allow or cease the flow of liquid or gas. The plunger opens the valve and turns on the solenoids, allowing flow. The valve closes when it is deactivated.

Example: A coffee maker uses a 2-way solenoid valve to regulate the water flow into the coffee grounds. The solenoid is activated when you start brewing, and water flows through the valve to brew your coffee. The solenoid deactivates after the brewing cycle is finished, closing the valve to stop the water flow.

Three Way (3-Way) Solenoid valve:

3-way solenoid valve has 3 ports and 2 potential flow paths. These valves are used when the flow of liquid or gas needs to be redirected between two different outlets. The solenoid can be activated to direct the flow in one way, and deactivated to direct the flow to the other way.

Example: A 3-way solenoid valve, for instance, could be used in an automatic car wash to regulate whether water is sent to the soap dispenser or the high-pressure spray nozzles, depending on whether cleaning or foaming is necessary.

Four Way (4 ways) Solenoid Valve:

These valves have four ports and are commonly used in applications where the direction and flow of a liquid or gas must be controlled. They have two solenoids that work together to control the movement of the piston and control the pathways.

Example: Suppose you have a lawn, a flower bed, a vegetable garden and a shrubbery area in your garden. Each of these areas needs different amounts of water, so you need to control the sprinkler system accordingly.

You can do this by using a 4 way solenoid (solenoid valve) for your lawn zone and for your vegetable garden zone.

When you turn on the lawn zone valve, the water is directed to the lawn sprinklers. When you turn on the vegetable garden valve, water is directed to your vegetable garden sprinkler.

This means that you can effectively water different parts of your garden with a single 4 way Solenoid valve.

Normally Closed (NC) Solenoid Valve:

A normally closed (NC) solenoid valve is a type of valve that closes when there is no current flowing through it. Normally, the valve is open and flow is allowed when you turn on your solenoid. The valve automatically closes when there is a power outage. This type of valve is often used in applications that require safety.

Example: An emergency stop system in an industrial setting may use a normally closed valve to prevent the flow of dangerous liquids. The valve closes automatically when there is an emergency, such as a power outage or when there is a leak.

Normally Open (NO) Solenoid Valve:

When the solenoid is not activated, the valve is open. When the solenoid is activated, the valve closes, and stops the flow. This type is used when you want flow to be the default state and you need active control to halt it.

Example: In a gas furnace, a normally open solenoid valve controls the flow of natural gas to the burner. The solenoid valve is activated when the thermostat signals a need for heat, allowing gas to flow and igniting the burner. As soon as the desired temperature is reached, the solenoid deactivates, and the flow of gas is stopped.

Direct-Acting Solenoid Valve:

The solenoid directly controls the movement of the plunger, which opens or closes the valve in this arrangement. Because of its simplicity, it is appropriate for low-pressure applications.

Example: Assume you begin a laundry cycle in your washing machine. The machine’s water inlet system’s direct-acting solenoid valve is activated.

The valve opens, allowing water to enter the drum of the washing machine. The solenoid valve remains open as the drum fills with water.

When the desired water level is reached, the washing machine’s control system deactivates the solenoid valve, causing it to close and cease the flow of water. This ensures that your washing machine has enough water to complete the wash cycle.

Pilot-Operated Solenoid Valve:

These valves use a combination of small pilot valves and a diaphragm to control the main valve. By operating the pilot valve, the solenoid controls the flow through the larger valve. The type is suitable for high-pressure applications and can handle higher flow rates.

Example: Assume you have a garden irrigation system with a pilot-operated solenoid valve. When you turn on the solenoid, it opens the pilot valve, allowing a small amount of water to reach the diaphragm of the main valve. The pressure generated by this little flow unlocks the main valve, allowing water to flow from the higher water tank and water your plants.

When you deactivate the solenoid, the pilot valve closes and the diaphragm of the main valve also closes, thereby, stopping the flow of water. The pilot-operated solenoid valve controls the flow of water and efficiently irrigates your garden by utilising the decision-making capacity of a pilot valve.

Latching Solenoid Valve:

This type of solenoid valve has two coils, one for opening and the other for closing. This makes them energy-efficient and excellent for battery-operated gadgets because they do not need a constant power source to maintain their condition.

Example: A latching solenoid valve can be used in a battery-operated irrigation system to regulate the water flow into different areas of a garden. Energy is conserved because the valve, once programmed to open or close for a certain zone, stays in that condition until modified.

High-pressure Solenoid Valves:

High-pressure valves are designed to withstand high pressure conditions without leakage or failure. They are constructed using high-quality materials.

Examples: A high pressure solenoid valve can be used to power heavy machinery or tools in a high pressure industrial hydraulic system.

Minimal-Pressure Solenoid Valve:

These valves are suitable for applications with minimal pressure requirements. They are frequently utilized in circumstances where precision and accuracy in flow control are critical.

Example: In a lab where you need to make sure that you get the exact amount of reagent or chemical, a valve with a low pressure can make sure you get exactly what you need without wasting any of it.


A water solenoid valve is a smart and versatile device that plays an essential role in controlling the flow of water in a variety of applications. Think of it as a water traffic light that precisely directs its movement. The valve contains a coil inside it which acts like a small electromagnet. When current flows through the coil, it creates a magnetic field. This field has a special power – it can attract or repel the piston, which acts as a switch that controls the flow of water.

The solenoid valve turns on when an electric current is present. It’s like turning a switch. The force of the current pushes the plunger forward, creating a path for water to pass through. It’s like the valve is telling the water to go ahead.

The magnetic field disappears when the electricity is turned off, and the plunger returns to its original position, thereby closing the valve.  Now, the valve tells the water, “Hold on, not right now.”


This simple yet ingenious mechanism allows solenoid valves to be used in a wide range of applications. For instance, in a washing machine, a solenoid valve controls the flow of water into the drum. When you start a wash cycle, the solenoid valve opens to let water in. When the cycle is done, it closes to stop the flow.

Similarly, in garden irrigation systems, solenoid valves manage when and where water is distributed to keep your plants happy. When it’s time to water a specific area, the solenoid valve opens to allow water through. When that area has had enough, the valve closes.

Solenoid water valves are like guardians of our water resources. It makes sure that water flows as per where it is needed and when it is needed. Here, Electricity and magnetism works together to make sure that water is flowing to where it is needed. They make life easier and more efficient by controlling water flow with efficiency and accuracy.


What is a Solenoid Switch?

A solenoid switch is an electromechanical device. It regulates the motion of a mechanical part, frequently referred to as a plunger or armature, using an electromagnetic field. It performs the function of a switch that can be operated remotely, converting electrical signals into mechanical motion. Automotive systems, industrial machinery, and consumer electronics all use solenoid switches in some capacity.

Working Principle of a Solenoid Switch:

The operation of a solenoid switch is rooted in the principles of electromagnetism. It involves a coil of wire wound around a magnetic core. When an electric current is passed through the coil, it produces a magnetic field around the core.

The plunger or armature is propelled by this magnetic field’s force on it. The balance between the magnetic force produced by the coil and the opposing spring force governs the movement of the plunger.

When the coil is activated, the magnetic force overcomes the spring force and the piston is pulled into the solenoid, making or breaking the connection. In most solenoid switches, the movement of the piston opens or closes the circuit. This action can be used for anything from turning on a light to starting a vehicle.


What is a Solenoid Lock?

A solenoid lock is an electromechanical device that uses the principles of electromagnetism to control the locking and unlocking mechanism of a door or other access points. It combines the power of electricity and magnetism to secure or release a locking mechanism, providing enhanced security and convenience.

How Does a Solenoid Lock Work:

Solenoid locks work by combining electrical current, magnetic fields, and mechanical elements. Following is the  step-by-step breakdown of how it works:


A solenoid lock consists of several key components: a coil of wire, a plunger or armature, a locking mechanism (such as a bolt or latch), and often a spring.

Energizing the Coil:

 When an electric current flows through the coil wound around the solenoid, a magnetic field is generated. This magnetic field surrounds the coil and extends to the plunger.

Magnetic Attraction:

The plunger is made up of a material that attracts the magnetic field created by the energized coil. This magnetic attraction pulls the plunger towards the coil.

Mechanical Action:

As the plunger moves, it engages with the locking mechanism. Depending on the design, the plunger can either extend or retract the bolt or latch that secures the door. When the plunger moves, it physically locks or unlocks the access point.

Spring Force: Many solenoid locks incorporate a spring that counteracts the magnetic force of the plunger. This spring provides the necessary tension to return the plunger to its original position when the electric current is turned off.

Control and Activation: Electronic control of solenoid locks is achieved through the use of an electronic system, which may be a keypad, a card reader, or a remote control. Upon authorization, the electronic system transmits an electrical signal to power the solenoid coils, which in turn triggers the plunger to engage the locking or unlocking system.

Security and Convenience: Solenoid locks offer enhanced security since they can be integrated into access control systems. They can also provide convenience by allowing remote unlocking or automatic locking based on predetermined conditions.

Types of Solenoid Locks:

Fail-Safe Solenoid Locks: These locks are designed to unlock when power is removed. In case of a power failure or emergency, the lock automatically releases, allowing quick exit.

Fail-Secure Solenoid Locks: These locks remain locked when power is removed. They provide added security as they stay locked even during power outages.

Magnetic Locks: Also known as maglocks, these locks use the repelling force between a magnet and an electromagnet to secure doors. They are widely used in access control systems.

Applications of Solenoid Locks:

Solenoid locks are used in various settings and applications, including:

Access control systems for buildings, offices, and secure areas

Electronic and smart locks for homes and apartments

Safety and emergency exit doors

Industrial facilities and warehouses

Commercial establishments and retail stores

High-security environments like banks and government buildings


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