A wax motor is a linear actuator that is sometimes used to replace a magnetic solenoid in an application where a short range of linear motion is required.
The wax motor has three principal components:
When the electric heater is energized, the wax block is heated and it expands, driving the plunger outwards. When the electric current is removed, the wax block cools and contracts and the plunger is withdrawn, usually by spring force applied externally or by a spring incorporated directly into the wax motor.
Depending on the particular application, wax motors may have three potential advantages over magnetic solenoids:
Wax motors were perhaps most famously used on Maytag's line of front-loading clothes washers where they experienced an unfortunately-high failure rate and have now been substantially replaced by magnetic solenoids.
Wax motors are also commonly used to drive zone valves in hydronic (hot water) heating systems.