Confusing burner???

[Joe]

Very weird thing happened today, while testing my internally fired mamod i discovered a few minor problems but thanks to the help of other 16mm modelers they are now sorted however i discovered that when the burner, gas tank and gas jet are taken out of the loco and set up the gas flows fine but the burner will not work even though gas is coming out of it it wont light! when we put the burner etc back in the loco and fired it up it worked perfectly (if a bit to perfectly as I think flames burnt a rubber seal on the reverser block which is causing a steam leak, i will turn the gas down next time!) any ideas why this was happening? it doesn't really matter as the loco steams well its just something i found quite confusing. I guess that's mamods for you but at least it works well in the loco
cheers
Joe

[DLRdan]

Burners that are fitted to interanally fired locos wont work outside the boiler. This is because the flame is kept on the burner by the boiler tube (im sure there is a very scientific reasons why but this is what I was told). I have only ever seen one other internally fired mamod, all the others are externally fired.

[Joe]

ah ok cheers, that explains it it works fine when its in the boiler now i imagine internally fired engines are more economical than externally fired ones

[steamie1]

The air ratio has to be specific to work. Mamod have had many issues over the years when changing new models, getting the air holes/ shield right. There is more in this game. Chris on the Mamod section highlights some issues with early new models. All more clever than first seemed.

[mikewakefielduk@btinterne]

Internally fired boilers are more efficient than externally fired ones as, being surrounded by water there's a greater heating surface. Even so they're not great compared with a multi-tubed boiler but frankly it rarely matters assuming the design of the external pot boiler has an effective heat shield. Not always the case with some Mamods as owners found when the tank decals started to melt and the paint blister.

As for why the internal burner won't light, as already said, its the gas to air mix. If you look at many Accucraft locos you'll see two small holes where the burner goes into the boiler. One is for the steam pipe and the other for secondary air. If you block the second hole the loco won't light properly.