Pilot light
Encyclopedia
A pilot light is a small gas
flame
, usually natural gas
or liquefied petroleum gas, which is kept alight in order to serve as an ignition source for a more powerful gas burner.
systems, flamethrower
s, and hot air balloon
s. While most commercial kitchens still rely on pilot lights for burners, ovens, and grills, current residential systems typically use an electrical ignition. More commonly known as standby on modern remote control fires.
The above methods are examples of the use of "fail-safe
" safety protection.
s of gas power (between 8 and 16 Gigajoules/year). That said, the heat from a pilot light in many appliances (furnaces, space heaters, hot water heaters) is generally released in the same chamber as the primary burner.
electrical arc or spark
between two electrode
s close to the gas flow from the burner that is to be lit. Fail-safe design for such a system requires the burner flame to be detected by passing an electric current through the flame, which is "received" by a control box, whilst the flame is established there will be a flow of electrons through the flame so the control box keeps the appliance working, should the flame extinguish, the electron flow will be broken so causing the control box to shut down the appliance.
A red-hot surface can also be used to provide ignition. Such igniters are often made of silicon carbide
, silicon nitride
, or another material that is durable under prolonged exposure to extreme heat. Hot-surface igniters are commonly used in cooking oven
s and boilers.
A disadvantage to modern alternatives requiring high voltage is that the appliances become useless during a power outage. Pilot light solutions work independently of the electrical system.
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
flame
Flame
A flame is the visible , gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone...
, usually natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
or liquefied petroleum gas, which is kept alight in order to serve as an ignition source for a more powerful gas burner.
Origin
During the American colonial period, people kept a small flame called a "pilot" burning in order to quickly light a fire for a fireplace or for a cooking stove.Uses
Common applications include household water heaters, central heatingCentral heating
A central heating system provides warmth to the whole interior of a building from one point to multiple rooms. When combined with other systems in order to control the building climate, the whole system may be a HVAC system.Central heating differs from local heating in that the heat generation...
systems, flamethrower
Flamethrower
A flamethrower is a mechanical device designed to project a long controllable stream of fire.Some flamethrowers project a stream of ignited flammable liquid; some project a long gas flame. Most military flamethrowers use liquids, but commercial flamethrowers tend to use high-pressure propane and...
s, and hot air balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology. It is in a class of aircraft known as balloon aircraft. On November 21, 1783, in Paris, France, the first untethered manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air...
s. While most commercial kitchens still rely on pilot lights for burners, ovens, and grills, current residential systems typically use an electrical ignition. More commonly known as standby on modern remote control fires.
Safety protection
In natural gas furnaces, water heaters, and room heating systems, a safety cut-off switch is usually included so that the gas supply to the pilot and heating system is shut off by an electrically operated valve if the pilot light goes out. This cut-off switch usually detects the pilot light in one of three ways:- A sensor filled with mercuryMercury (element)Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
is used to detect the heat of the pilot light. Contraction of the mercury results in sufficient pressure to operate an electrical switch that interrupts the flow of electricity and shuts off the gas valve when the pilot light goes out. - A photoresistorPhotoresistorA photoresistor or light dependent resistor is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor or CdS device, from "cadmium sulfide," which is the material from which the device is made and that actually exhibits the...
is used to detect the light from the pilot lamp. When the pilot light goes out, electrical circuitry connected to the photoresistor shuts off the gas valve. - Use of a pilot generator or a thermocoupleThermocoupleA thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...
in the flame provides heating appliance safety as it generates enough electrical current from the burning flame to hold the gas valve open. If the pilot light goes out, the pilot generator cools off and the current stops, closing the gas valve.
The above methods are examples of the use of "fail-safe
Fail-safe
A fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel....
" safety protection.
Energy waste
In domestic heating systems with pilot lights it has been estimated that on average half the total energy usage is from the pilot light, each pilot light using between 240 and 500 WattWatt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s of gas power (between 8 and 16 Gigajoules/year). That said, the heat from a pilot light in many appliances (furnaces, space heaters, hot water heaters) is generally released in the same chamber as the primary burner.
Modern alternatives
An alternative to the pilot light is a system that provides a high voltageHigh voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...
electrical arc or spark
Electric spark
An electric spark is a type of electrostatic discharge that occurs when an electric field creates an ionized electrically conductive channel in air producing a brief emission of light and sound. A spark is formed when the electric field strength exceeds the dielectric field strength of air...
between two electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s close to the gas flow from the burner that is to be lit. Fail-safe design for such a system requires the burner flame to be detected by passing an electric current through the flame, which is "received" by a control box, whilst the flame is established there will be a flow of electrons through the flame so the control box keeps the appliance working, should the flame extinguish, the electron flow will be broken so causing the control box to shut down the appliance.
A red-hot surface can also be used to provide ignition. Such igniters are often made of silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
, silicon nitride
Silicon nitride
Silicon nitride is a chemical compound of silicon and nitrogen. If powdered silicon is heated between 1300° and 1400°C in an atmosphere of nitrogen, trisilicon tetranitride, Si3N4, is formed. The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen...
, or another material that is durable under prolonged exposure to extreme heat. Hot-surface igniters are commonly used in cooking oven
Oven
An oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...
s and boilers.
A disadvantage to modern alternatives requiring high voltage is that the appliances become useless during a power outage. Pilot light solutions work independently of the electrical system.