Gas furnace safety valves, used for preventing deadly gas leaks in your home, are attached to regulate gas flow to any gas-powered appliance. A gas valve detects unheated gas on its own and shuts off the gas supply in order to prevent fires and explosions and don't require manual activation.
Gas valves have two functions: controlling pressure and ensuring the safety of the gas-supplied device. Without a proper gas valve, gas pressure would not reach the device properly. Too much pressure could lead to explosions that can do severe damage to a home and lead to injury and death, and too little pressure does not allow the device to function properly. A gas valve helps to regulate the pressure to the right amount.
The safety functionality of a gas valve is automatic. In the event of gas not properly being lit by the furnace starter, the gas valve shuts off to prevent an excess of gas leakage. If the valve did not do this on its own, there would be a possibility of gas leaking into the air in large amounts, risking fire and explosions. This sensor detects excess unheated gas and does not activate if the gas is burning in normal operation unless the valve is faulty.