We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is a Solenoid?

Michael Pollick
Updated May 17, 2024
Our promise to you
About Mechanics is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At About Mechanics, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

A solenoid is a device that converts energy into linear motion.  This energy may come from an electromagnetic field, a pneumatic (air-powered) chamber, or a hydraulic (fluid-filled) cylinder.  These devices are commonly found in electric bell assemblies, automotive starter systems, industrial air hammers, and many other machines that rely on a sudden burst of power to move a specific part.

In order to understand the underlying principle, a person can examine a typical pinball machine.  At the beginning of play, a steel ball rests on a rubber-tipped plunger that is held in place by a compression spring, which means it has no energy to move the ball when at rest.  The player's hand provides additional energy as the plunger assembly is pulled back.  Upon release, the spring forces almost all of the plunger pin's kinetic energy on a small area of the steel ball.  The ball is flung into the playing field and the pinball game begins.  This manual plunger is a rudimentary example of a solenoid.

The difficulty with using manual pinball plungers on other machines is that someone must constantly pull the spring back and release the energy by hand. An improved solenoid would provide its own means of pulling back on the pin and releasing it under control.  This is the principle behind a simple electric one, in which a metallic cylinder acts as the "plunger."

A compression spring holds this metal pin partially out of an electromagnetic housing.  When power from a battery or electric generator flows around the electromagnet, the metal pin or cylinder is magnetically drawn inside the housing, much like the player's hand pulls the plunger back in the pinball example.  When the electric current stops, the pin is released and the compression spring sends it forward with significant force.  The pin may strike the inside of a bell or forcefully eject a part from a molding machine.  Many electronic machines contain numerous solenoids.

Other types depend on compressed air for their power.  A single piston may be placed in an airtight cylinder connected to a source of highly-compressed air.  A strong internal spring may hold the piston in place until the air pressure has reached a predetermined level and then the piston is released.  The compressed air is allowed to escape as the piston drives forward.

Because the energy released by a solenoid can be concentrated, pneumatic ones are popular for heavy tools and machining applications which require substantial power.  A jackhammer is a good example of this type in action.  The central piston is driven by air into the concrete, then the recoil of the hammer returns the piston to its original position.

An even more powerful solenoid uses hydraulics as its source of power.  The piston or pin is seated in a cylinder filled with a hydraulic fluid.  As this hydraulic fluid fills the cylinder, everything is pushed forward, including the piston or pin.  As the piston travels towards a piece of metal or other target, the fluid buildup becomes very resistant to compression, and the piston will concentrate all of the cylinder's energy on whatever it encounters, even the heaviest titanium.

When the solenoid has released all of its energy, the hydraulic fluid drains out of the chamber and the piston is drawn back to its original position.  This action can take place in a matter of seconds.  This type is so powerful that it is generally used only for the heaviest projects.  Wave pools use them to release the giant stoppers at the bottom of their holding tanks.  Aircraft manufacturers use this type to bend titanium and other heavy metals.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Pollick
By Michael Pollick
As a frequent contributor to About Mechanics, Michael Pollick uses his passion for research and writing to cover a wide range of topics. His curiosity drives him to study subjects in-depth, resulting in informative and engaging articles. Prior to becoming a professional writer, Michael honed his skills as an English tutor, poet, voice-over artist, and DJ.
Discussion Comments
By anon310695 — On Dec 26, 2012

I want to know what a Honda Accord 2003 solenoid looks like.

By treme2005 — On Jul 21, 2010

In automobiles like cars and trucks, the starter solenoid is part of an automobile starting system. Commonly referred to as the "starter relay," it receives a large electric current from the car battery and a smaller electric current from the ignition switch. When the key is turned to start the car, the small electric current forces the starter solenoid to close a pair of heavy contacts. This relays the large electric current to the starter motor.

By megaMouse — On Jul 21, 2010

The rotary voice coil is a rotational version of the solenoid. Rotary voice coils are typically used in devices like disk drives.

Michael Pollick
Michael Pollick
As a frequent contributor to About Mechanics, Michael Pollick uses his passion for research and writing to cover a wide...
Learn more
About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.