STEMCO Capillary Switch

Capillary and Snap Disc Thermostat Switch Control and Limit

Capillary and Bi-Metal Style Thermostats

Control vs. Limit Switches

Some may say that Capillary and Bimetal Snap Disc style thermostats are old technologies. Many of today’s machines use a digital control and sensor to control the heating or cooling device, such as a chiller or heating element. We manufacture a digital switch too. When a machine needs higher reliability to operate, or cannot survive a digital control failure or power interruption, engineers will use something a more reliable such as a capillary or snap disc thermostat switch.

Bi-metal Snap Disc Thermostat Switch

Highly Reliable Thermostat Switches

These devices are based on physics and not an electrical scheme or chip set. In more critical heating and cooling applications multiple switches are involved, one being a control and the other being a limit switch. The control switch turns something on and off when a given temperature is reached. Simple examples being a fan when a desired temperature is reached on a wood stove moving the warm air until the temperature has cooled or a compressor to a chiller when your refrigerator gets too warm.

Highly Critical Limit Thermostat Switch

To prevent a critical scenario a second limit switch is also used. The limit is designed to interrupt the critical event so the machine can survive the critical scenario. A classic example is a hot water heater. One control switch will turn the heating elements, on and off, at a set temperature to maintain that temperature. A second limit thermostat switch also be used to prevent the heating element from going into a runaway condition overheating the systems and causing a critical event.

Capillary Style Thermostat Switch

Capillary & Bi-Metal Style Always Operate

The capillary switches and bi-metal snap disc switches are based on physics, no matter what happens to the power being supplied the switch will operate because of the physical characteristics of the switch. The capillary switch is designed around a medium such as a fluid expanding or contracting as temperature changes and does not require any power to operate. The bi-metal snap disc thermostat uses the physics of expansion and contraction of metals to operate again without any power required. The bottom line is yes, they are older technology, but they are used in the design of modern products because they work.

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