Brick arches

i know these are found in the firebox of a loco but what do they actually do??? i was wondering why lord nelson had to be pulled out of service due to a collapsed brick arch

 

This is one for the M.I.C. section. A brick arch deflects the hot gases at the lower end of the firebox away from the tube plate, thus creating a smooth flow of the gases through the tubes to the smokebox. It also protects the tubeplate and tube ends from direct contact with the heat of the fire.

 

Hi, if you have a look on this website, it should give you a good idea to what the Brick Arch does. http://www.greatwestern.org.uk/basic1.htm

 

The brick arch has more than one function.
Firstly, as has been stated, it protects the ends of the tubes not only from the action of the fire, but also from any cold air coming in through holes in the front of the fire.
Secondly, it lengthens the path that the volitile gasses in the coal have to take through the fire box, so they are burned off in the firebox raising the temperature of the fire box, and meaning that the only gasses taken up the tubes are exhaust gasses, making combustion more effective and the loco more free steaming.
Thirdly, once hot, it acts as a heat resovoiur, meaning that the boiler will steam more freely, on less coal once the brick arch is hot, and keeping the steaming ability up when there is less pull on the fire.
If you don't get the brick arch hot, you are in trouble!

 

In answer to the question about why the loco was pulled out of trafic, if the whole of the brick arch goes with the loco in traffic, then half the fire box will not be providing any steam, as the rubble from the brick arch will block it, and even if you could did the rubble out then the loco will not steam and the tube plate be dammaged as stated in my last post

 

Despite the name, a lot of brick arches, nowadays, are in fact concrete. They are cast in situ over a series of wooden formers. The concrete is of a particular grade suitable for the job.

 

Quite correct, or concrete bricks, pre cast, in a sort of one size fits all (or mast at least) fassion, so that when part does collapse, you just drop another brick in