Industrial heating systems often operate in conditions where electronics mounted directly to the heater become unreliable. Heat, vibration, moisture, and restricted space can cause failures or make service difficult. To avoid these issues, many OEMs and control panel builders use external temperature controllers for industrial heaters, heat trace systems, and process applications. These controllers allow safe, remote temperature regulation and system shutdown outside of the immediate heat zone.
At Stemco, a division of Senasys, we manufacture the bulb and capillary thermostat switches that are installed inside these external temperature controllers. Our mechanical switches provide either adjustable temperature control or manual reset overtemperature protection. These switches serve as the core temperature control components inside external enclosures used across a wide range of industrial heating systems.
Contact us to request OEM pricing or to schedule a consultation with our engineering team.
Industrial Applications for External Temperature Controllers
External controllers allow control components to be mounted away from harsh environments while still maintaining accurate thermal sensing. Inside each controller, a mechanical switch receives temperature input from a bulb positioned near the heater. As a result, this setup keeps wiring simple, protects the control element, and improves system longevity.
Common industrial applications include:
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Over-the-side immersion heaters that provide direct fluid heating in tanks and drums. These systems often rely on adjustable temperature controllers to maintain steady fluid temperatures and include a manual reset switch as a high-limit safety shutoff.
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Circulation heaters used in closed-loop water, oil, or chemical systems. These heaters require stable temperature regulation to protect pump systems and process integrity. The temperature controller allows easy adjustment during setup or system changes.
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Duct heaters and air process heaters that regulate airflow temperature in drying, makeup air, or ventilation systems. External temperature controllers are mounted away from airflow paths to protect the switch and simplify service access.
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Heat trace systems installed along piping to prevent freezing or maintain process fluid temperature. The temperature controller houses the switch, while the sensing bulb attaches directly to the pipe or ambient area being monitored.
These external temperature controllers use Stemco switches as the control mechanism, offering a mechanical solution that eliminates the need for integrated electronics at the heater.
Bulb and Capillary Switches for Temperature Control and Safety
We manufacture two standard switch types, both designed to be installed inside external temperature controller housings:
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Manual Reset Bulb and Capillary Switches
These are used as overtemperature safety shutoffs. If the process temperature exceeds the setpoint, the switch opens and remains open until someone manually resets it. This configuration protects equipment and personnel from overheating conditions. -
Adjustable Bulb and Capillary Switches
These allow the installer or operator to fine-tune the control setpoint using an accessible dial. Adjustable switches provide precise temperature control for steady-state heating applications.
Each model uses a liquid-filled sensing bulb and capillary tube, which transfers temperature changes to a mechanical diaphragm. As the fluid expands or contracts with temperature shifts, the diaphragm moves and actuates the switch inside the controller.
Key Features of Stemco Bulb and Capillary Switches for Heater Controllers
OEMs, panel builders, and process engineers use bulb and capillary switches because they perform consistently in demanding industrial environments. Our products are designed and tested for accuracy, durability, and safety.
Key benefits include:
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UL and cUL certification for regulatory compliance
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SPDT switch action for both control and alarm/shutdown logic
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Wide range of sensing temperatures and setpoint options
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Manual reset and adjustable models to suit different system types
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Made in the USA with short lead times
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100% functional testing prior to shipping
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Backed by direct engineering and customer support
If you’re building or specifying external temperature controllers for industrial heaters, heat trace systems, or fluid process equipment, Stemco can supply the core switching components. Our adjustable and manual reset bulb and capillary switches handle the challenges of industrial temperature control.
For additional information on our bulb and capillary switches, visit the product page.
