Hi What is the component on a GWR steam locomotive called? and why is it in place of a steam dome normally? its usually brass... I have an Airfix 2-6-2 kit that I'm motorizing, that is like that and would like to know more about it, Thanks for any info...
As I understand your question, I believe —
Boiler diameters increased to supply more steam as locomotives were pushed to hightr limits of horsepower and speed. Track clearances did not.
If the GWR 2-6-2 is anything like the New York Central Niagara* 4-8-4 the 102" boiler diameter at its largest course didn't allow for a traditional steam dome. Instead, a slotted dry-pipe was installed to draw the steam from the highest level above the water-line. *It is not.
The main purpose of the steam dome being to provide a point where steam could be drawn for locomotion and appliances without drawing boiler water into the dry pipe.
[edit]
I seem to have mis-interpreted your question. I believe you are asking about the safety valve shield located just ahead of the whistle on the boiler top. The boiler feed water pipes come in from each side.
There are excellent photos of same here:
http://www.gwr.org.uk/no-prairies.html
safety-valve_bonnet by Edmund, on Flickr
More great photos here:
https://www.flickr.com/photos/brianews/albums/72157669538653672
Hope that helps, Ed
gmpullman
While the conical centre section does indeed cover the safety valves, the "shoulders" each side cover the boiler feed check valves, generally called "clack valves" in the UK. Pipes from the injectors are mounted each side, entering at the recesses shown in the drawing.
LMS locomotives after 1933 had similar covers without the safety valve cone. Some of these had a dummy dome cover (on boilers without actual domes) or with just the angular "shoulder" shape continued across.
Peter