Caltherm

Thermal Actuators

This page is designed to provide you with a basic understanding of the operation and performance criteria of these devices and to illustrate the sizes and styles available. If none of the actuators found on this page fulfill your requirements, Caltherm Engineers will custom design an actuator for your application. Caltherm Thermal Actuators are available in various operating temperatures of 15 degrees F(-9 degrees C) to 270 degrees F(132 degrees C).

Thermal Actuators manufactured by Caltherm Corporation permit the transforming of heat energy into mechanical energy via the movement of a piston. Their working principal is based on the large increase in volume of a thermo sensitive material which is heated and changes from a solid to a liquid state. The force developed by this expansion is transmitted to a piston to perform work. Caltherm Thermal Actuators are constructed to retain their operating characteristics in spite of extreme temperatures, serve vibrations, and fluctuations of pressure.

Caltherm Thermal Actuators are being used in a variety of thermostatic applications. Typical applications include: automotive controls, trucks, buses, aerospace, marine, home and commercial heating controls, anti-scald devices, warning systems, compressors and home appliances.

Caltherm Corporation manufactures an extensive range of Thermal Actuators designed to respond within specific temperature ranges. This array of actuators incorporates two types of designs, shown below, which differ in construction and performance:





1) Squeeze-Push Design

(Figure A)- The squeeze-push construction uses a "glove finger" shaped synthetic rubber bag which surrounds a stainless steel piston. The resulting pressure collapses the bag forcing the piston out by both a lateral squeeze and vertical push.

This design has an advantage over the flat diaphragm design in that it is generally less costly and, for comparably sized actuators, are capable of providing a longer piston stroke. This design is best used in light to medium duty applications.

2) Diaphragm Design

(Figure B)- In this design, the expansion is separated from the guide portion of the actuator by a molded synthetic rubber diaphragm. Above this, within the guide, is an oversized plug of a similar material. An increase in temperature causes the thermo sensitive material to expand, applying pressure to the rubber plug which is forced into reduced diameters in the piston guide. This extruding action causes movement can be utilized to operate a valve, mechanical linkage, electric switch, or other device. The plug and diaphragm type has clearly proven the most practical and reliable for heavy duty applications.

Typical Performance Curve


Shown in the chart on the right is a typical performance curve for a Caltherm Thermal Actuator. As shown, the majority of the actuator's power stroke is achieved between a curve can be modified to accommodate different temperature and stroke requirements. The return stroke depicts the performance as the actuator cools.

The difference between the power and return stroke curves describes a typical hystersis loop which is inherent to thermal actuators of the squeeze-push and diaphragm designs. Though skilled design techniques and material selection, Caltherm engineers maintain the smallest hysteresis loops possible.

The response time of a Caltherm Thermal Actuator will vary with respect to the temperature of the medium in which it is immersed (i.e. air, water, oil, etc.), the load on the piston, and the amount of cup surface exposed. Response time can be controlled to some degree by expansion material formulation.

Thermal Actuator Specifications

Drawing Index    Photo Index

ALL DIMENSIONS & PERFORMANCE SPECIFICATIONS ARE APPROXIMATE

If you would like additional information on Thermal Actuators, or just have questions, please feel free to call or e-mail us at the information below.