Thermal actuator is also called thermal wax element, wax element, thermostatic element. The thermal actuator can convert heat energy into mechanical energy, and has the function of rapidly and automatically transmitting mechanical action after induction of temperature changes. Its mechanical action is derived from thermal expansion material. Thermal actuator is not affected by the surrounding environment. It is the key component of various temperature regulation and control systems. It has the advantages of wide temperature adjustment range, accurate temperature control, simple structure, reliable performance and so on. Thermal actuator is widely used in automotive industry, building heating, sanitary bathing, HVAC, solar water heater, petrochemical, shipbuilding, industrial automatic control, fire extinguishing, household appliances, safety devices, aerospace and other fields.
In line with internal sealing methods of thermostatic element, thermal actuator can be divided into squeeze-push type, diaphragm type and piston type.
Types of thermal actuator
1. Squeeze-push type
A sealed capsule contains wax and transfers its thermal expansion through an elastomeric bag to the piston. When the surrounding medium warms, the wax expands and generates movement; an external spring returns the piston during cooling.
This construction is often considered where a larger stroke is required. The final suitability depends on the application’s temperature characteristic, force and service conditions.
2. Diaphragm type
In a diaphragm design, wax expansion acts on a diaphragm and transfers movement through a plug to the piston. The guide supports the moving parts while an external spring provides the return movement during cooling.
Diaphragm layouts can be considered for applications that need a compact, controlled movement path.
3. Plunger-piston type
A plunger-piston design uses wax expansion within a sealed cup to move a piston. It can be configured for control systems where packaging, stroke and load requirements need to be balanced.
Common terminology
Initial position: the piston position measured from a reference level before activation.
Full-open stroke: the piston displacement at the specified full-open temperature.
Overstroke: additional piston displacement under the maximum specified operating condition.
Hysteresis: the difference between heating and cooling response curves.
Sensitivity: the response time under a defined test condition.
