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2. Central heating - Wikipedia

   en.wikipedia.org/wiki/Central_heating

   An expansion tank contains compressed gas, separated from the sealed-system water by a diaphragm. This allows for normal variations of pressure in the system. A safety valve allows water to escape from the system when pressure becomes too high, and a valve can open to replenish water from the normal water supply if the pressure drops too low ...

3. HVAC control system - Wikipedia

   en.wikipedia.org/wiki/HVAC_control_system

   After the control of air flow and temperature was standardized, the use of electromechanical relays in ladder logic to switch dampers became standardized. Eventually, the relays became electronic switches, as transistors eventually could handle greater current loads. By 1985, pneumatic controls could no longer compete with this new technology ...

4. Damper (flow) - Wikipedia

   en.wikipedia.org/wiki/Damper_(flow)

   This damper can switch the electrical power to control additional "slave" dampers, minimizing the electrical load on the damper's control circuitry and power transformer A zone damper (also known as a Volume Control Damper or VCD ) is a specific type of damper used to control the flow of air in an HVAC heating or cooling system.

5. Furnace (central heating) - Wikipedia

   en.wikipedia.org/wiki/Furnace_(central_heating)

   The fourth category of furnace is the high-efficiency condensing gas furnace. High efficiency condensing gas furnaces typically achieve between 90% and 98% AFUE. [3] A condensing gas furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. The primary gain in efficiency for a condensing gas furnace, as ...

6. Forced-air - Wikipedia

   en.wikipedia.org/wiki/Forced-air

   A simple electric heating element warms the air.; When the thermostat calls for heat, blower and element come on at the same time. When thermostat is "satisfied", blower and element shut off.

7. Shutdown valve - Wikipedia

   en.wikipedia.org/wiki/Shutdown_valve

   A safety shutoff valve should be fail-safe, that is close upon failure of any element of the input control system (such as temperature controllers, steam pressure controllers), air pressure, fuel pressure, current from a flame detector, or current from other safety devices such as low water cutoff, and high pressure cutoff.