Not all Bulbs, Probes and Capillary Tubes use a fluid fill, some use a gas. There are a large number of different fluids and gases used. This is based on:

• What material is being sensed for temperature
• Temperature range of the switch
• Other external requirements to the switch

There are also other engineering and design requirements that are taken into account when a fill material is chosen. A large number of them use a variation of an alcohol fill. Some even have odors added so a leak can be detected.

No matter which style or model you choose, all of the capillary thermostat switches operate using the same physics. A fluid or gas is encapsulated in a metal and when the temperature changes it either expands or contracts. This change moves a diaphragm which is in touch with a snap action switch and either opens or closes a circuit.

For more information about STEMCO capillary switches, click here to contact us.