There is a good chance you’ve used multiple solenoids at some point today. They help start your car, ring your doorbell, and do hundreds of other things for you every day. But, what is a solenoid and how does a solenoid work?
A solenoid works by producing an electromagnetic field around a movable core, called an armature. When compelled to move by the electromagnetic field, the motion of that armature opens and closes valves or switches and turns electrical energy into mechanical motion and force.
For being such a large part of our world, solenoids are simple mechanisms that require only a basic grasp of physics most of us learned in middle school. Understanding them is not difficult, and you don’t have to know any mathematical formulas to learn their secrets.
What Is a Solenoid?
At the simplest level, a solenoid is a length of wire coiled around a core. The core often has two parts-- a stationary core and a moveable one, which is the armature. The two parts are spring-loaded.
When electrical current goes through the wire, it creates a magnetic field that moves the armature away from the stationary core (or toward it, depending on the solenoid’s use and construction). When the current stops, the spring snaps the armature back into its original position.
This back-and-forth motion makes this type a linear solenoid, although there are also rotary solenoids that are a little more complex.
To function, a solenoid must have three things:
- Coiled wire
- A movable core
Take away the coiled wire, and you have nothing. Take away the electricity, and you have a spring. Take away the core, and you’re only holding an electromagnet.
In a car’s ignition system, these elements combine to move the armature, which allows for the completion of the circuit that ignites your engine. Once you let go of your key and it moves away from the “start” position, the solenoid deactivates, the armature moves back to its previous position, breaking the circuit. This way, your car’s ignition stops trying to start the engine, as it’s already running.
While a solenoid uses electromagnetism, it is not itself an electromagnet. It only uses electromagnetism to do its work. Despite this, many people use the terms interchangeably.
For an visual reference on solenoids, see the video below:
A solenoid gets dissected starting at the 5:40 mark, allowing you to see that it is nothing more than a coil of copper wire. It takes the electrical current to make the solenoid work.
Find an automotive-specific video here:
In this one, you’ll find much information on a car’s starter solenoid, you’ll get a look inside one of them, and you will learn about what makes these units go bad, including why that clicking noise your car makes when it won’t start is an indicator of a bad solenoid.
What Is a Solenoid Valve?
Solenoid valves are just like any other valve in that they regulate the flow of gasses or liquids. The presence of a solenoid in them allows those valves to open or close via electricity.
These types of valves can be made in two different ways: normally open and normally closed.
In a solenoid valve’s resting position-- off-- no current runs through the wires, and the movable core rests against the base of the valve. By doing so, it seals the valve, as the liquid or gas behind it cannot get through.
Sending electricity through the coil of wire creates the magnetic field, that field causes the core to lift up, and the liquid or gas can now pass freely through the valve. Turning off the electricity drops the core back down, closing the valve and cutting off the gas or liquid flow. This is the function of a normally closed valve, which stays closed until electricity is used to open the valve.
A normally open solenoid valve uses the same fundamentals, but is designed to work in reverse. When in the off position, the core remains in the up position, allowing media to flow through the open valve. Powering the valve on will force the core to move down, shutting off the flow and closing the valve.
The Strength of a Solenoid
If you’ve ever used a pneumatic tool, you’ve used a small solenoid. Your compressor had pressurized air in it. You pressed the trigger of your nail gun because you wanted a puff of that compressed air to drive a nail in for you. When you did so, a solenoid valve opened up for a fraction of a second, allowing a dose of that pressurized air to shoot from the compressor to the gun and drive that nail.
Moving a valve as small as that one doesn’t take much power, but a solenoid in a larger tool-- perhaps managing more significant quantities of liquid or gas-- needs more. The power available from a solenoid comes from the number of coils in the wire and the current sent through it.
Governed by Ampere’s law, which is a mathematical equation that considers these elements to determine the strength of the electromagnetic field, the magnetic field equation allows for determining how many coils and how much current one needs to adequately power a solenoid valve.
Stronger or weaker solenoids find use depending on need. A large, powerful solenoid with many coils and a large electrical current is unnecessary for making your doorbell ring. A small solenoid can accomplish this.
But a solenoid valve on an oil derrick would need to be much more powerful. While all solenoids are electrical-- you cannot have an electromagnet without electricity-- the variety of jobs they do requires different types.
- Electrical. This term governs all solenoid valves, as electricity must be involved.
- Pneumatic. These solenoid valves allow for the movement and suppression of gasses such as air, nitrogen, and carbon dioxide.
- Hydraulic. A valve that governs the motion of liquids, from water to bourbon to gasoline.
When you start looking for them, you will find that solenoids and solenoid valves are everywhere in modern life, and they make many tasks we do every day much more manageable.
Testing a Solenoid
Your solenoid valve may stop opening and closing from time to time, or the solenoid in your car may not start your car one day. Diagnosing these problems is key to fixing them, so there are few simple ways to do that.
The simplest way is with a compass. Because your solenoid runs on electromagnetism, there will not be a magnetic field surrounding it if the solenoid itself isn’t functioning.
By placing a compass near the solenoid and then activating that solenoid, you’ll know immediately if it is the problem or there is some other mechanical issue. If your compass needle jumps, the solenoid created a magnetic field. If not, then your solenoid is not getting the electricity it needs.
In this case, you can further determine the issue with a multimeter. Before that, though, your first step is to check the connections. If your positive or negative terminals are disconnected or are in any way faulty, the solenoid cannot work even if it is in pristine condition. Even if the connections look good, you should use your multimeter to determine the solenoid’s continuity.
Once you’ve determined that the connections are good, switch your multimeter over to its resistance setting. If you get a reading over 0.3 ohms, the unit isn’t functioning as it should. It is not conducting enough electricity to work and needs replacing.
For more information on how to diagnose and fix a problem, see our solenoid valve troubleshooting resource.
Solenoids and solenoid valves occur nearly everywhere in our modern world. We use them to start cars, operate dialysis machines, control dishwashers, even manipulate our speakers into producing music from an electrical signal. While our lives would be very different without them, solenoids are simple creations.
Requiring only wire, a magnetic core, and an electrical current, functioning solenoids can be fashioned in a middle school science class, but they help us accomplish hundreds of tasks, some of which would be impossible without them.
Still Have Questions
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