Wax Motor

Recorded: Sept. 17, 2026, 8 p.m.

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Wax motor - Wikipedia

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1
Design

2
Applications

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2.1
Aerospace Controls

2.2
Mixing Valves - HVAC

2.3
Laundry washing machines

2.4
Water heating systems

2.5
Dishwashers

2.6
Greenhouse vents

2.7
Paraffin microactuator

3
See also

4
References

5
External links

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Wax motor

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From Wikipedia, the free encyclopedia

Wax-based linear actuator device
A wax motor manufactured by iSwell
A wax motor is a linear actuator device that converts thermal energy into mechanical energy by exploiting the phase-change behaviour of waxes.[1] During melting, wax typically expands in volume by 5–20% (Freund et al. 1982).
A wide range of waxes can be used in wax motors, ranging from highly refined hydrocarbons to waxes extracted from vegetable matter. Specific examples include paraffin waxes in the straight-chain n-alkanes series. These melt and solidify over a well-defined and narrow temperature range.
Design[edit]
The principal components of a wax motor are:
An enclosed volume of wax
A plunger or stroke-rod to convert the thermo-hydraulic force from the wax into a useful mechanical output
A source of heat such as:
Electric current; typically a PTC thermistor, that heats the wax
Solar radiation; e.g. greenhouse vents
Combustion heat; e.g. excess heat from internal combustion engines
Ambient heat
A sink to reject heat energy such as:
Convection to cooler ambient air
Peltier effect device arranged to transfer heat energy away
When the heat source is energized, the wax block is heated and it expands, driving the plunger outwards by volume displacement. When the heat source is removed, the wax block contracts as it cools and the wax solidifies. For the plunger to withdraw, a biasing force is usually required to overcome the mechanical resistance of seals that contain the liquid wax. The biasing force is typically 20% to 30% of the operating force and often provided by a mechanical spring or gravity-fed dead weight applied externally into the wax motor (Duerig 1990, p. 214).
Depending on the particular application, wax motors potentially have advantages over magnetic solenoids:
They provide a large hydraulic force from the expansion of the wax in the order of 4000 N (corresponding to roughly 400 kg or 900 lb at standard gravity) (Tibbitts 1988, p. 13).
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 can be operated entirely passively by exploiting ambient sources of energy. Given that a variety of melting-points are possible for the wax used inside the motor, one can be selected to match the range of ambient operating temperatures in a given application. In this way the wax can be melted and solidified within this range by the transfer of thermal energy. When co-located with the heat source, wax motors can be operated without the need for an additional external power source.
Applications[edit]
This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2014) (Learn how and when to remove this message)
Aerospace Controls[edit]
Wax motors are used heavily in the aerospace industry where they are utilized to control fuel, hydraulic, and other oils critical to safe flight today in modern airplanes.[2]
Mixing Valves - HVAC[edit]
Wax motors are contained inside "self actuating" thermostatic mixing valves, where the wax motor senses thermal change and responds accordingly to yield a desired mixed fluid temperature.
Laundry washing machines[edit]
Some front load washing machines use wax motors to engage the door lock assembly. When a cycle is started, a wax motor is actuated pushing a pin outward and locking the door. This design has cost, reliability and safety advantages. In moist conditions a wax motor costs less for equivalent reliability than an electromagnetic solenoid or motor latch. It has a predictable passive release delay. If power is lost the door remains briefly locked, designed to be longer than the high speed spin cycle coast-down time, then reliably unlocks as the wax cools.
Water heating systems[edit]
Wax motors are also commonly used to drive zone valves in hydronic (hot water) heating systems.
Thermostatic radiator valves
Dishwashers[edit]
They are used in many dishwashers to release the detergent dispenser door latch. The wax motor acts like a solenoid when activated by the dishwasher's timer or control, and the piston operates the mechanism which then releases the catch for the dispenser door. They are also used to control the exhaust vent for the drying cycle.
Greenhouse vents[edit]
Wax motors are widely used to operate the temperature regulating vents of greenhouses.
In this application, as the ambient temperature within the greenhouse increases, the wax melts, activating the plunger and opening the vents. When the greenhouse temperature has cooled sufficiently, the wax cools and solidifies, allowing the vents to close again.
Paraffin microactuator[edit]
A paraffin microactuator is a type of wax motor, often fabricated by microelectromechanical systems (MEMS) technology or sometimes precision mechanics.[3]
See also[edit]
Wax thermostatic element
Thermostatic radiator valve
References[edit]

↑ Setright, L. J. K. (1976). "Cooling". In Ian Ward (ed.). Anatomy of the Motor Car. Orbis. pp. 61–62. ISBN 0-85613-230-6.
↑ Group, Techbriefs Media (October 2018). "Thermostatic Solutions for Temperature Control Applications". www.aerodefensetech.com. Retrieved 2021-03-15. {{cite web}}: |last= has generic name (help)
↑ Ogden, Sam; Klintberg, Lena; Thornell, Greger; Hjort, Klas; Bodén, Roger (30 November 2013). "Review on miniaturized paraffin phase change actuators, valves, and pumps". Microfluidics and Nanofluidics. 17: 53–71. doi:10.1007/s10404-013-1289-3. S2CID 85525659.

Freund, M.; Csikos, R; Keszthelyi, S; Mozes, Gy (1982). Paraffin products: properties, technologies and applications. Budapest, Hungary: Hungarian academy of sciences. ISBN 963-05-2680-8.
Duerig, T.W. (1990). Engineering aspects of shape memory alloys. Oxford: Butterworth-Heinemann. ISBN 0-7506-1009-3.
Tibbitts, Scott (1988). "High output paraffin actuators: Utilization in aerospace mechanism". NASA Technical Reports Server. Hanover, MD: NASA Center for AeroSpace Information (CASI). Retrieved May 31, 2019.
External links[edit]
Wax Motor Manufacturer - Rostra Vernatherm
General Thermal Actuator - Wax Motor Information
Wax Motor and Thermoactuator Manufacturer | iSwell

Retrieved from "https://en.wikipedia.org/w/index.php?title=Wax_motor&oldid=1372579147"
Category: ActuatorsHidden categories: Articles with short descriptionShort description matches WikidataArticles needing additional references from January 2014All articles needing additional referencesCS1 errors: generic name

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Wax motor

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A wax motor functions as a linear actuator device that converts thermal energy directly into mechanical energy by harnessing the phase-change behavior of waxes. When heated, wax typically undergoes a volumetric expansion of 5 to 20 percent, a phenomenon detailed by Freund et al. in 1982. The core design of a wax motor comprises an enclosed volume of wax, a plunger or stroke-rod responsible for converting the resultant thermo-hydraulic force into useful mechanical output, a heat source, and a heat sink. The heat source can be supplied by various means, including electric current (often via a PTC thermistor), solar radiation, combustion heat, or ambient heat. Heat is removed through a heat sink, which may involve convection to cooler ambient air or the use of a Peltier effect device to dissipate thermal energy.

The operation is governed by thermal expansion and contraction. When the heat source activates the wax, the wax expands, driving the plunger outward through volume displacement. Conversely, when the heat is removed, the wax contracts and solidifies. To facilitate the retraction of the plunger, a biasing force, typically provided by a mechanical spring or gravity-fed dead weight applied externally, is necessary to overcome the mechanical resistance of the seals containing the liquid wax, often amounting to twenty to thirty percent of the operating force (Duerig 1990).

Wax motors possess distinct mechanical advantages compared to alternatives like magnetic solenoids. They are capable of generating a substantial hydraulic force, potentially reaching 4000 Newtons, which corresponds to roughly 400 kilograms or 900 pounds at standard gravity (Tibbitts 1988). Furthermore, the actuation and release processes are smooth and gentle, as, unlike instantaneous electromagnetic systems, the motion is gradual. Because the system functions as a resistive load rather than an inductive load, wax motors controlled by TRIACs do not necessitate the inclusion of snubber circuits. An additional significant benefit is the potential for passive operation; by selecting a wax with a melting point suitable for ambient operating temperatures, the motor can be operated solely by ambient thermal energy without an external power source when co-located with a suitable heat source.

The practical applications of wax motors are diverse across various engineering fields. In the aerospace industry, they are utilized for controlling critical systems such as fuel, hydraulic fluids, and other oils essential for safe flight. In the field of HVAC, wax motors are integrated into self-actuating thermostatic mixing valves, which sense thermal changes to adjust the output fluid temperature. In household appliances, wax motors have been employed in front-load washing machines to engage door lock assemblies, offering advantages in cost, reliability, and safety over electromagnetic latches, particularly due to their predictable passive release delay. Similarly, they drive zone valves in hydronic hot water heating systems. In dishwashers, these motors release detergent dispenser door latches and control exhaust vents during the drying cycle. Furthermore, wax motors are utilized in greenhouse vents, where increasing ambient temperature melts the wax to open the vents and allows cooling to cause solidification and closure. A specialized form is the paraffin microactuator, which can be fabricated using microelectromechanical systems or precision mechanics.