How do capillary thermostats work for HVAC Systems?

Capillary thermostats are commonly used in HVAC systems to regulate temperature by controlling the operation of heating or cooling equipment. Here's how they work:

Sensing Temperature: The thermostat contains a capillary tube filled with a temperature-sensitive fluid (often mercury, alcohol, or a special gas). One end of the tube is connected to the temperature sensing element, while the other end is connected to a bulb that is placed in the area being monitored (such as near the heating or cooling coils).

Fluid Expansion: When the temperature changes, the fluid inside the capillary tube expands or contracts. If the temperature rises, the fluid expands, and if it drops, the fluid contracts.

Mechanical Action: The expansion or contraction of the fluid causes a pressure change inside the capillary tube. This pressure then pushes or pulls a diaphragm or mechanical switch inside the thermostat, activating or deactivating the HVAC equipment.

Control: When the thermostat reaches a predetermined temperature set point, it opens or closes the electrical contacts that control the HVAC system. For instance, when the desired temperature is exceeded, the thermostat will turn off the heater or air conditioner. If the temperature falls below the set point, it will activate the system to maintain a comfortable environment.

Capillary thermostats are effective for HVAC applications due to their reliability, cost-effectiveness, and ability to function in various environmental conditions. They're often used in systems where precise temperature control is needed, like in refrigeration units, air conditioners, and heating systems.

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