Thermostats



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tarix05.02.2018
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THERMOSTATS

  • THERMOSTATS


  • To regulate the temperature of a substance or space by controlling the flow of gas to the burner.

  • To add to the convenience, utility, economy and, in some cases, safety of the appliance.





Snap acting

  • Snap acting

  • Gas flows at full rate then shuts off when temperature is reached. Cooling may take place before thermostat comes back on.



Operation

  • Operation

  • Rod and tube has different coefficient of expansion.

  • Outer tube and inner rod fixed at one end.





Liquids expand when heated and contract when cooled.

  • Liquids expand when heated and contract when cooled.

  • A bellows is opened and closed by this expansion and contraction.

  • By attaching a gas valve to the bellows gas flow can be controlled.





Sensing bulb of thermostat is filled with gas.

  • Sensing bulb of thermostat is filled with gas.

  • When temperature increases, the gas pressure in the bulb increases.

  • This increases the bellows acting on the gas valve.



If two different metals are bonded together and an increase in temperature takes place, the expansion will cause the bimetal strip to bend upwards or downwards depending on the location of the metal with the higher expansion rate.

  • If two different metals are bonded together and an increase in temperature takes place, the expansion will cause the bimetal strip to bend upwards or downwards depending on the location of the metal with the higher expansion rate.

  • Bimetal thermostats are:

  • used to control the fan of a duct air heater; or

  • used as room thermostats.







Purpose: To regulate the temperature of a substance or space by controlling the flow of gas to the burner.

  • Purpose: To regulate the temperature of a substance or space by controlling the flow of gas to the burner.

  • Thermostat types

  • Rod and tube

  • Liquid expansion

  • Vapour pressure

  • Bimetal

  • Thermostat function

    • Snap acting
    • Modulating


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