Of pilot lights and flame out switches

[kwame]

Hi folks hope all is well. I have a little problem understanding furnace controls. .How does a furnace/automatic gas oven's ignition system start.Providing,it gets switched on,'a pilot light' glows, which inturn ignite the burner.Question:what happens to 'pilot light 'subsequently?Does it stay on or go off? and how ?(is it timed)? Those machines have flame out switches to prevent flame from straying out;in which case the flame out switch shuts off gas(fuel) to burner. Question :does flameout switch shutoff fuel indefinitely till resetting manually or it resumes supply of fuel on its own? And how?
Greetings

 

[kubeek]

The pilot light should be lit at all times. If the fire goes out and the flame out switch trips, then the furnace shuts off indefinitely. This is because the furnace needs the pilot light on in order to be able to light the main flame, and since there is no mechanism to ignite the pilot flame then it cannot do anything else but sit and wait till someone comes around and ignites the pilot flame manually.

Also, some types of furnaces don´t have a pilot flame but use electric spark ignition to directly ignite the main flame.

 

[crutschow]

If by "pilot light" you mean a glow plug, that only lights until the flame ignites.

On my furnace, if the flame detector doesn't detect a flame during turn-on it will shut off the gas momentarily and then attempt to restart the furnace a few times. After that it locks out and you have to reset (power down) the furnace to get it to restart. I found this out when my flame detector became dirty and the furnace became erratic in it's startup. A simple cleaning of the flame detector probe solved the problem.

 

[KeepItSimpleStupid]

There are many systems. But let's take an early non-electronic one for a dryer. Glow plug heats tube, tube opens pilot, glow plug turns on flame, Pilot flame heats main burner valve. Main burner on. Main burner keeps valve open. When an where the electric is removed from the ignitor and if the pilot is turned off - never looked,

Modern stuff may use flame rectification or IR,

A furnace and an oven may have different sorts of controls in terms of the number of trials allowed.

 

[kwame]

If by "pilot light" you mean a glow plug, that only lights until the flame ignites.

On my furnace, if the flame detector doesn't detect a flame during turn-on it will shut off the gas momentarily and then attempt to restart the furnace a few times. After that it locks out and you have to reset (power down) the furnace to get it to restart. I found this out when my flame detector became dirty and the furnace became erratic in it's startup. A simple cleaning of the flame detector probe solved the problem.

 

[KeepItSimpleStupid]

I'm not sure if the main burner ignites directly, It would seem that if it did, you could "blow out the match" so to speak.. I thn=ink it makes more sense to ligtt a pilot first and then the main burner especially when it comes to furnaces. Stoves and ovens could be different.

You have glow plugs and spark ignitors to contend with.

For some idea as to how they work, I would refer you to this manufacturer: www.fenwalcontrols.com/utcfs/Templates/Pages/Template-54/0,8063,pageId%3D4858%26siteId%3D375,00.html

 

[kwame]

I am apparent reference to electric spark ignition that i am told, is installed on modern rotating rack oven ;used for igniting the burner when the oven gets switched ON.After the burner starts giving out heat what happens to the "pilot light'.I need help as furnaces are used in this part of the world owing to plenty sunshine.

 

[KeepItSimpleStupid]

Ovens: See: http://www.appliance411.com/faq/gas_range_ignition_systems.shtml

 

[Reloadron]

I am apparent reference to electric spark ignition that i am told, is installed on modern rotating rack oven ;used for igniting the burner when the oven gets switched ON.After the burner starts giving out heat what happens to the "pilot light'.I need help as furnaces are used in this part of the world owing to plenty sunshine.

Since you mention "spark" then glow plugs are out I guess. Most of what you are asking depends on the system. While many gas fired systems are similar in operation they also vary slightly in how they work. Additionally, it depends on locations globally. Some countries have laws governing their operation while in other countries I have seen systems that scare me because they are unsafe.

Look over the link KISS provided and see what systems and methods in that link look like what you have. Good link as it clearly shows several different designs.

Ron

 

[ramuna]

Hi,
In the UK, most domestic central heating systems use natural gas fired boilers. The ignition circuit (which is more accurately called a gas release circuit, see below) has a number of switches in series. All the switches must be simultaneously closed for ignition to occur. The master controller is a time switch which closes from say, before the occupants rise from sleep to just after breakfast & then again from just before the occupants return home from work to supper-time. Then there is a thermostat switch which only closes if the ambient temperature is below the temperature preset on the thermostat. The pilot light is a small (less than 2 cms in length) gas flame inside the boiler, which is permanently lit (although it can get extinguished on rare occasions, by say very strong winds blowing down the boiler's chimney in a storm). The pilot light's flame contacts the main burner and, crucially, a thermocouple. The thermocouple senses whether the pilot light is lit. The thermocouple controls a relay, which is the final switch in the ignition circuit. When all the switches are closed, the gas supply to the burner is switched on. The thermocouple ensures that gas is never sent to the burner when the pilot light is off, since that gas would leak out of the boiler into the house and cause an explosion hazard. See the following for more details: https://home.howstuffworks.com/pilot-light.htm