Capillary Switch Monitor Air Tunnel TemperatureIn a commercial or industrial hot air tunnel dryer used for shrink wrap or for drying, a double bulb and capillary thermostat switch and a snap disc thermostat switch are commonly used to control the air tunnels temperature and limit the high temperature of the system. Click the diagram on the right for more information.

Generally P/N 351-253890 double bulb and capillary thermostat is found in these systems, as well as P/N 351-254243 can be used in it’s place.

For more information on monitoring temperature in hot air tunnels or using a tunnel dryer switch, continue reading below.

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Double Bulb and Capillary Switch

The double bulb thermostat switch activates the heating elements when the machine is turned on. When the temperature of the tunnel gets to maximum temperature the capillary switch shuts the heating elements down. Once the minimum temperature is hit the heating elements are turned on again and the cycle is started over.

The heating elements are wired through a second device on the capillary switch which is affixed to another bulb, and when the current draw is increased heat is created. If the second bulb senses that temperature, or the current draw is too high, the capillary switch will shut the heaters down. Parts can now be sent through the heated air tunnel by a conveyor at a controlled speed.

Our capillary thermostat switches have a temperature range between 0°-700°F, with a max ambient temperature of 250°. The temperature range determines when the capillary thermostat will close, or engage the electrical circuit, and when it will automatically reset, or open. These capillary thermostats can also be manually reset for when you need to call special attention to a temperature malfunction. The temperatures can be fixed or adjustable.

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Bi-metal Snap Disc Thermostat Switch

A second limit, snap disc thermostat switch, is placed in the airstream that will sense a temperature beyond the first control switches. These switches are calibrated to the maximum temperature and will shut down the heating elements to prevent a critical event. This second temperature switch may be a manual reset requiring human intervention to re-start or automatic reset based on a pre-determined temperature.

Senasys designs and manufactures a variety of fixed thermostat switches including 1/2″ or 3/4″ bi-metal snap disc style, or a digital switching solution. Our fixed thermostat switches will change states at a preset temperature, -50-450°F. The thermostat switches are used in equipment to open or close a circuit when temperature changes. A wide range of temperature settings, tolerances and differentials available; and a variety of terminals and mounting options.

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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.