At it’s heart, an electric motor is converting a pushing and pulling motion into a rotational motion. The coils on the rotor all pull in opposite directions from opposing sides, which makes things spin. What if we didn’t have opposing sides and we weren’t trying to spin? We’d make the ‘rotor’ pop up and down instead, wouldn’t we?
This sort of device is called a solenoid, and you’re probably surrounded by them. Devices like this are used on the locks and starter in your car, in valves, precision medical equipment, driving and aircraft simulators, industrial safety locks, door locks, and more. They’re pretty much everywhere. This widespread use comes down to how simple they are and how many operations just need to push and pull something. To make a motor push something, you need that motor, gears, and linkages. A solenoid just needs a coil of wire and some iron.
The best known use of solenoids in our office of course, is Solenoid Valves. We’ll get into those in more detail later, but in general, they’re amazingly simple, reliable, and easily repaired valves. The hardware consists of the solenoid coil, an armature, some springs, and a diaphragm on a specially machined pipe. Their key selling points are their response time and simplicity for light-duty applications.
How Does It Work?
There’s not much to a basic solenoid. You have a coil, an armature (the part that moves), an outer casing, an inner casing, and often a plastic inner lining. That’s really all there is to it. When you apply power to the coil, it generates a magnetic field. The polarity of this field will either attract or repel it’s armature. If the armature is attracted, it gets sucked down inside the coil. If it’s repelled, it’s pushed outwards until it it’s stopped by the outer casing.
Variations on this design generally change the form of the outer case, the location of the spring, and in some cases even allow the actuator to fully pass through the casing so it can push and pull simultaneously. There’s also custom windings to consider and the choice of metal for the armature, which influences the torque and electrical efficiency overall.
The design isn’t bullet proof, there are parts that do eventually fail. In some cases, the coil shorts out and can no longer produce a magnetic field. Sometimes the plastic lining fails and causes a short between the armature and winding. Sometimes dirt or rust seizes up the armature. As the armature and coil age, they may not perform up to the specifications for their application.
The Wrap Up
What did you think? Did we get something wrong? Got something for us to cover next time? Let us know in the comments below.