Automatic Reset Snap Disc Thermostats

Application Data: 1/2” Snap Disc Thermostats- Auto and Manual Reset

Snap Disc Thermostats Basics

The snap disc thermostat incorporates a small, curved metal disc made of two different metals bonded together often referred to as a bimetal. These metals are chosen because they have different thermal expansion characteristics. This means they expand and contract at different rates when heated or cooled. Essentially, it’s a layered disc of two metals that react differently to heat. This is the heart of a snap disc thermostat.

When the temperature rises, the metal that expands more will cause the disc to bend or curve. Conversely, when the temperature drops, the metal that contracts more will cause the disc to bend in the opposite direction. This bending is designed to reach a point where the disc rapidly “snaps” from one curved shape to another. This snapping motion is what triggers a switch that either turns an electrical circuit on or off. This predictable and repeatable action makes bimetal discs ideal for temperature-sensitive applications.

They react very quickly to temperature changes. They can directly handle relatively high electrical currents or indirectly when wired through a contactor or relay to switch higher amperage loads.

Snap disc thermostats help control temperature in many devices. They are often used to prevent overheating, acting as a safety overtemperature device. While they can directly regulate temperature, they’re more often used for over-temperature protection. 

Types of Snap Disc Thermostats 

There are two types of snap disc thermostats. Automatic Reset (Auto Reset) and Manual Reset Thermostats. 

Auto reset thermostats automatically return to their operational state once the temperature falls below a set point range. Manual-reset thermostats include a push to reset button that requires physical intervention to reset after triggering. The manual reset construction provides a crucial safety measure in situations where over-temperature events necessitate investigation. 

Positioning and Installation

The snap disc must be positioned where it can accurately sense the temperature it’s intended to monitor. This often means placing it in close proximity to the heat source or in a location where airflow is representative of the overall system temperature.

Proper thermal contact is very important. The sensor must be able to react quickly to the temperature it is monitoring.

Common mounting methods provided on Vulcan Comstat brand snap disc thermostats include 

• Flange mount: Our standard stock models are provided with a rotating flange to accommodate multiple positions. The flange locks into place when the thermostat is installed
• Threaded stud mount: A common option that includes an M5 stud for threaded mounting into the application

Common applications

• In everyday appliances.
• In complex equipment like aircraft and medical devices.
• In commercial food equipment, adhesive dispensing devices, and laboratory instrumentation.
• In HVAC (Heating, Ventilation, and Air Conditioning) systems.
• In electronic control systems.

Temperature Ranges

Vulcan Comstat brand snap disc thermostat models are available in a wide range of temperatures, from -49°F (-45°C) to 797°F (+425°C).