Gas Appliance Components
Gas valves, orifices, burners, manifold adjustments, flame sensors, rollout switches, safety controls, and appliance data plates.
- Identify gas valve types and their operation
- Explain orifice sizing and burner function
- Describe flame detection and safety control systems
Leçon 1
Gas Valves & Orifices
Gas Valve Function
The gas valve is the primary control component. It regulates gas flow to the burners based on signals from the thermostat and safety controls. Modern gas valves combine multiple functions:
- Manual shut-off (on/off/pilot selector)
- Pressure regulation (reduces supply to manifold pressure)
- Safety shut-off (closes if flame is not detected)
- Modulation (on modulating furnaces, varies gas flow)
Orifice Function
The orifice (or spud) is a precision-drilled fitting that meters the correct amount of gas to each burner port. Orifice size depends on:
- Gas type (natural gas vs. propane)
- Input rating required
- Manifold pressure
Natural Gas Orifice
Larger opening - natural gas has lower BTU/cu ft
More gas volume needed per BTU
Lower manifold pressure (3.5" WC)
Propane Orifice
Smaller opening - propane has higher BTU/cu ft
Less gas volume needed per BTU
Higher manifold pressure (10" WC)
Wrong Orifice = Danger
Using a natural gas orifice on propane causes severe overfiring (too much gas). Using a propane orifice on natural gas causes underfiring. Always verify the orifice matches the gas type during installation and conversion.
Gas valves regulate pressure and flow based on thermostat demand. Orifices meter the correct gas amount to each burner. Natural gas orifices are larger than propane orifices. Using the wrong orifice for the gas type is a serious safety hazard.