Capillary Switch Monitor Air Tunnel Temperature

Commercial and industrial hot air tunnel dryers, used for shrink wrapping and drying, rely on precise temperature control. This control is achieved with a combination of double bulb and capillary thermostat switches and snap disc thermostat switches. These components work together to maintain optimal temperatures and ensure safety. Below, we explore how these switches function and their technical specifications. For detailed information, click the diagram on the right.

Typically, systems use part numbers P/N 351-253890 (double bulb and capillary thermostat) and P/N 351-254243. For more on monitoring temperature in hot air tunnels or using tunnel dryer switches, continue reading.

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Double Bulb and Capillary Thermostat Switch

Stemco 351-254287 Capillary Thermostat

The double bulb thermostat switch activates the heating elements when the machine starts. As the tunnel temperature reaches its maximum set point, the capillary switch shuts down the heating elements. Once the temperature drops to the minimum set point, the heating elements reactivate, starting the cycle anew.

  • Temperature Sensing: The primary bulb monitors the tunnel temperature. When the temperature reaches the maximum set point, the fluid in the capillary tube expands, creating pressure that triggers the switch to shut off the heating elements.
  • Safety Mechanism: A secondary bulb monitors current draw, which generates heat. If the current draw becomes too high, the capillary switch activates to shut down the heaters, preventing overheating.
  • Temperature Range: Our capillary thermostat switches operate between 0°-700°F, with a maximum ambient temperature of 250°F. These thermostats can be manually or automatically reset to address temperature malfunctions. They come with fixed or adjustable temperatures.

Technical Specs:

  • Operating Temperature: 0°-700°F
  • Max Ambient Temperature: 250°F
  • Reset Options: Manual and automatic
  • Temperature Settings: Fixed or adjustable

For more information about our capillary thermostat switches, visit the product page.

Bi-Metal Snap Disc ThermostatsSnap Disc Thermostat Switch

Snap disc thermostat switches provide additional safety by sensing high temperatures in the airstream. Calibrated to the system’s maximum temperature, they shut down the heating elements to prevent critical events. These switches can be manually reset, requiring human intervention, or automatically reset based on a pre-determined temperature.

  • High-Temperature Detection: Placed in the airstream, the snap disc thermostat detects when temperatures exceed safe operating limits.
  • Safety Shutdown: The switch opens the circuit, cutting power to the heating elements to prevent hazards.
  • Reset Mechanisms: Configured for either manual or automatic reset based on system requirements.

Technical Specs:

  • Operating Temperature Range: -50°F to 450°F
  • Switch Types: 1/2″ or 3/4″ bi-metal snap disc styles or digital switching solutions
  • Customization: Various temperature settings, tolerances, differentials, terminals, and mounting options

For more information on our standard snap disc thermostat options, click here to visit the Senasys website.

Double bulb and capillary thermostat switches, along with snap disc thermostat switches, are essential for maintaining precise temperature control and safety in commercial and industrial hot air tunnel dryers. Understanding their operation and technical specifications is needed for selecting the right components.

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Bulb & Capillary Thermostats

Original equipment manufacturers worldwide use thermostat switches designed and manufactured by STEMCO, a Division of Senasys. No matter which style or model you choose, all of the capillary thermostat switches operate using the same physics. A fluid is encapsulated in a metal and when the temperature changes the fluid either expands or contracts. This fluid change moves a diaphragm which is in touch with a snap action switch and either opens or closes a circuit.

Ambient Compensation

Our capillary thermostats can be ambient compensated to offset the differential in temperature which keeps our thermostat controls more accurate as it’s environment changes.

Custom Options

Capillary thermostat switches built by Senasys can also be built to customer specifications. This insures you get the exact control you want without paying for features you don’t need.