Wax motor
From Wikipedia, the free encyclopedia
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:
- A block of wax
- A plunger that bears on the wax
- An electric heater, typically a PTC thermistor, that heats the wax
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 When the electric current is removed, the wax block cools and contracts and the plunger is withdrawn (usually, by spring force applied externally or by a spring incorporated directly into the wax motor).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:
- Both the application and the release of the wax motor is not instantaneous, but rather, smooth and gentle.
- Because the wax motor is a resistive load rather than an inductive load, wax motors controlled by triacs do not require snubber circuits.
- Wax motors may survive situations where the plunger is blocked from full travel whereas some solenoids operating from alternating current will burn out unless the plunger travels all the way "home" (and thereby increases the inductance of the solenoid coil, reducing the current flow in the coil).
[edit] Real-world applications
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.
