When it comes to temperature control in industrial applications, HVAC systems and professional appliances, precision and reliability are essential requirements. In many cases, however, the point where temperature needs to be measured does not coincide with the location of the electrical contacts or control mechanisms.
This is precisely where capillary thermostats prove to be one of the most effective solutions. Thanks to a sensing bulb connected to the thermostat body by a thin capillary tube, temperature can be measured exactly where required while controlling the equipment remotely.
This technology continues to be widely used in numerous applications, including boilers, pellet stoves, thermo-fireplaces, air conditioning systems, professional catering equipment, medical devices and many other industrial sectors.
How does a capillary thermostat work?
The operating principle is based on the expansion of a fluid contained inside the sensing element.
The bulb, positioned where the temperature needs to be monitored, contains a fluid that expands as the temperature rises. This pressure variation is transmitted through the capillary tube to the sensitive element, commonly referred to as the expansion diaphragm.
The expansion diaphragm activates the internal electromechanical mechanism, opening or closing the electrical contact according to the detected temperature.
A capillary thermostat consists of four main components:
- the sensing bulb, which detects the temperature;
- the capillary tube, which transfers the pressure variation;
- the expansion diaphragm, which converts pressure into mechanical movement;
- the contact assembly, which controls the operation of the equipment.
This design provides accurate, reliable temperature control without requiring electronic sensing systems.
Temperature regulators and safety limiters: two different functions
Although they operate according to the same physical principle, capillary thermostats can perform different functions depending on the application.
Temperature regulators are designed to maintain a predefined operating temperature. Once the selected temperature is reached, the thermostat opens or closes the electrical contact, automatically regulating the operation of the equipment.
This is typically the case for ovens, boilers and heating systems, where maintaining a stable operating temperature is essential.
Safety limiters, on the other hand, intervene only when a maximum safety temperature is exceeded. Their purpose is to interrupt the electrical circuit, preventing overheating and protecting both the equipment and the system.
Some models also feature positive safety, ensuring that, in the event of thermostat failure, the electrical contact remains open to provide an additional level of protection.
The IMIT range for regulation and safety
Drawing on decades of expertise in thermoregulation, IMIT has developed a comprehensive range of capillary thermostats for a wide variety of industrial applications.
For temperature regulation, the range includes the TR2 and TRZ capillary temperature regulators, designed to provide precision and reliability even under demanding operating conditions.
For safety applications, IMIT offers the LS1 and LS3 safety limiters, developed to protect equipment and systems against overheating.
Overall, IMIT manufactures more than 7,000 capillary thermostat variants, differentiated by operating temperature, sensing bulb geometry, capillary length, electrical contact configuration and construction materials.
Operating temperature ranges extend from -30°C to 300°C, making these devices suitable for an extensive variety of industrial applications.
A highly specialised manufacturing process
Behind what appears to be a simple component lies a highly sophisticated manufacturing process.
Producing a capillary thermostat requires precision mechanical machining, assembly of miniature electromechanical components, filling the sensing system with a pressurised fluid and individual calibration of each device.
Every thermostat then undergoes rigorous functional testing to verify its accuracy, reliability and long-term durability.
One of the most distinctive manufacturing stages is the welding of the expansion diaphragm membrane, a highly specialised process that reflects IMIT’s manufacturing expertise.
Certified quality for worldwide applications
For more than forty years, the TR2, TRZ, LS1 and LS3 capillary thermostats have been among the flagship products of the IMIT range.
Each device is designed and manufactured according to strict international quality standards and complies with major industry certifications, including CE, ENEC, PED, TÜV, UL, CSA, EAC and DIN.
This combination of engineering expertise, manufacturing quality and operational reliability enables IMIT capillary thermostats to be successfully used in thousands of residential and industrial applications worldwide.