Buzz
Pilot lights remain in use, even though they tend to be a bit inefficient.
Eric Pearle/Getty ImagesIf you own an older furnace or water heater that operates on natural gas, or have gas logs in your fireplace, you've likely seen the small blue flame known as the pilot light. You may have even had the experience of relighting it when it goes out. Let's explore how the pilot light functions.
The concept of a pilot light is straightforward. Its role is to provide a flame that ignites the gas coming from the main burner. When the furnace "activates", a valve opens to release gas into the burner, and the pilot light ignites the gas.
Creating a pilot light is quite simple. It involves letting a small amount of gas flow through a tiny tube from the gas pipe. The gas escaping from the tube is then ignited and continues to burn constantly.
However, it's clear that the pilot light poses a potential safety risk. If the pilot light flame were to go out, gas would continue to flow from the tube. If this gas accumulated in your home and ignited, it could lead to an explosion. To prevent this, the pilot light tube has a valve that cuts off the gas flow in case the flame goes out.
This valve is an interesting piece of equipment. It must detect whether the pilot light is on or off, and it needs to do so without using any external electricity. How can a sensor for a pilot light be created to work reliably for many years without needing any power?
The solution to this problem is brilliant. The trick is to use the heat from the pilot light flame to generate electricity through a thermocouple.
Thermocouples generate electricity directly from heat by exploiting an electrical effect that happens at the junctions between different metals. For example, if you take two iron wires and one copper wire, twist one end of the copper wire to one iron wire and the other ends of the wires similarly, you will create two junctions. By heating one of these junctions with a flame and attaching the free ends of the iron wires to a voltmeter, you can measure a voltage.
In a pilot light system, one of the thermocouple's junctions sits within the flame of the pilot light. The electricity produced flows to a small electromagnetic valve, keeping it open. If the pilot light goes out, the thermocouple cools down quickly, halting electricity production and causing the valve to close.
To relight the pilot light, you need to press a button that manually opens the valve. Then, light the pilot and wait about 30 seconds for the thermocouple to heat up. Once it's hot, the thermocouple generates the electricity necessary to keep the valve open, allowing you to release the button.
The drawback of pilot lights is their high gas consumption. As a result, most modern appliances no longer use pilot lights, opting instead for a piezoelectric spark to ignite the burner.
