Thermostat - bi-metallic (mercury bulb)

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Bi-Metallic Thermostat Mercury Bulb Thermostat Bi-Metallic (Mercury Bulb)Gas Burner

Text in the illustration

the central hub of the bi-metallic coil is attached to the thermostat temperature setting dial - turning the dial down (counterclockwise) means that it will have to get even cooler before the mercury rolls down and closes the contacts
electrical circuit to gas valve or oil burner
when the coil warms up, it wants to straighten out - this tips the mercury switch so that the blob of mercury rolls away from the contacts, opening the circuit
circuit open
furnace off
bi-metallic coil
blob of mercury
contacts
as the bi-metallic coil cools, the mercury moves toward the contacts - closing the circuit and starting the furnace
circuit closed
furnace on

Generated explanation

The illustration shows two operating states of a bi-metallic coil thermostat with a mercury bulb switch. On the left, warming causes the coil to straighten and tilt the bulb so mercury moves away from the contacts, opening the electrical circuit and turning the furnace off. On the right, cooling tilts the bulb so mercury moves toward the contacts, closing the circuit and starting the furnace. The coil's central hub connects to the temperature-setting dial; turning the dial down counterclockwise requires a cooler temperature before the contacts close. The controlled circuit is identified as serving a gas valve or oil burner.

Components

bi-metallic coil mercury bulb switch electrical contacts thermostat central hub electrical circuit leads

Materials

bi-metallic metal strip mercury

Related illustrations

1261

Thermostat - bi-metallic (mercury bulb)

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Two side-by-side diagrams show the operation of a bi-metallic coil thermostat with a mercury bulb switch. On the left, warming the coil tips the bulb so mercury moves away from the electrical contacts, opening the circui

0762

Thermostat - bi-metallic (mercury bulb)

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Two diagrams show the operation of a bi-metallic coil thermostat with a mercury bulb switch. On the left, warming causes the coil to straighten and tip the bulb so mercury moves away from the contacts, opening the electr