Wax motor
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:
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 When the electric current is removed, the wax block cools and contracts and the plunger is withdrawn, usually by spring force applied externally or by a spring incorporated directly into the wax motor.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:
's line of front-loading clothes washer
s 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 valve
s in hydronic
(hot water) heating systems.
Linear actuator
A linear actuator is an actuator that creates linear motion .Mechanical and hydraulic actuation are the most common methods of achieving the linear motion...
that is sometimes used to replace a magnetic solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
in an application where a short range of linear motion is required.
The wax motor has three principal components:
- A block of waxWaxthumb|right|[[Cetyl palmitate]], a typical wax ester.Wax refers to a class of chemical compounds that are plastic near ambient temperatures. Characteristically, they melt above 45 °C to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents...
- A plunger that bears on the wax
- An electric heater, typically a PTC thermistorThermistorA thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor...
, that heats the wax
When the electric heater is energized, the wax block is heated and it expands
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
, 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 resistiveResistorA linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
load rather than an inductiveInductorAn inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
load, wax motors controlled by triacTriacTriac may refer to:* TRIAC , an electronics component* Triac , a green vehicle* Tiratricol, a common thyroid hormone analogue used for treating thyroid hormone resistance syndrome...
s do not require snubberSnubberA snubber is a device used to suppress voltage transients in electrical systems, pressure transients in fluid systems, or excess force or rapid movement in mechanical systems.-Electrical systems:...
circuits. - Wax motors may survive situations where the plunger is blocked from full travel whereas some solenoids operating from alternating currentAlternating currentIn alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
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.
Real-world applications
Wax motors were perhaps most famously used on MaytagMaytag
Maytag Corporation is an American home and commercial appliance company, headquartered in Newton, Iowa, that is a division of the Whirlpool Corporation.-Company history:...
's line of front-loading clothes washer
Washing machine
A washing machine is a machine designed to wash laundry, such as clothing, towels and sheets...
s 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 valve
Zone valve
A zone valve is a specific type of valve used to control the flow of water or steam in a hydronic heating or cooling system.In the interest of improving efficiency and occupant comfort, such systems are commonly divided up into multiple zones. For example, in a house, the main floor may be served...
s in hydronic
Hydronics
Hydronics is the use of water as the heat-transfer medium in heating and cooling systems.Some of the oldest and most common examples are steam and hot-water radiators. Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a...
(hot water) heating systems.