Steam Boiler/Firebox Replacement

[Ian J.]

Something I have just been wondering about. When a steam locomotive had/has its boiler replaced while in overhaul, was the firebox considered integral to the boiler, or was the boiler separated from the firebox in some way?

 

Also, as a follow on, if the firebox was included in the replacement, and the boiler/firebox was a different type, would the backhead of the firebox be different too?

 

TIA

 

Ian

[PhilH]

You need to understand the principles of loco boiler construction to understand any answer to this question - if you google locomotive boiler or somesuch it will take you to diagrams which will (hopefully) make it clearer.

 

Basically the firebox is an open bottomed box surrounded by water space. It is separate from the backhead, sides and partially the front of the firebox, but is held in place by stays which connect to the outside sheets of the boiler. The bottom of the firebox is held in place on all four sides by the foundation ring which is also obviously connected to the outside sheets of the boiler.

 

A loco boiler is very much a kit of parts consisting of flanged plates rivetted together (in some cases welded together). The boiler barrel is simply curved plates rivetted together, so replacement of parts is possible. Boiler parts are not usually interchangeable, so a new firebox would have to be made specifically for the specific boiler.

[Ian J.]

Thanks Phil, I see what you're saying.

 

If the boiler was being replaced with a different type, is it likely that the backhead would be changed too, or would that very much depend on whether the replacement boiler was designed to fit an existing backhead?

[PhilH]

Backheads are just part of boilers, if you see what I mean - they don't start with a backhead and nail a boiler onto it! The backhead is just the back sheet of the boiler with holes in for the controls and gauges etc..

 

They are much of a muchness in as much as they basically have the same bits and bobs on them. Different ways of doing things, RH and LH drive etc. the basics remain the same. that's why, for instance, on a gala I can go from a 1920s Western tank to an A4 to a Britannia and know what all the bits do.

[Ian J.]

OK, that's good to know.

 

Just to complete the picture, why I'm asking is that in order to understand the tooling bits required for my 4mm RTR Terrier project, there were four different boilers for them, Stroudley, Marsh, Drummond and Wainwright, and I wanted to know if the backhead would have been different between them. As it's an integral part of the boiler, then that suggests it would have been, even if only in detail differences.

 

Thanks for the help.

[34theletterbetweenB&D]

Ian,

 

You will need photos or drawings to compare for the boiler types of interest. UK Loco works practise was very conservative indeed, and for a 'same overall dimensions' boiler notionally or actually designed by different CME's, might well put the mountings for the significant fittings on the backhead in the same place every time. But that doesn't mean the backheads would then look completely alike. Designers often had pet fittings they would insist on, and the staying centres might well decrease with increases in boiler pressure for example.

[Ian J.]

I agree, 34.

 

Looking at photos I have of A1 Boxhill's backhead and A1X Martello's backhead, they look similar, but have detail differences. What I'm mainly concerned with is the Drummond and Wainwright backheads. I will need to see if I can find drawings of them (photos are highly unlikely to exist, bearing in mind they were only around for a short while in the early-ish 20th century).

 

Boxhill:

 

Martello:

[Boris]

Be wary of preserved examples, its hard to tell whats been done to them in the past 40 years or so, drawings or period photos are a more reliable source if you are wanting to model something specific within a certain time frame.

 

A broad rule of thumb anyway.

[PhilH]

Be wary of preserved examples, its hard to tell whats been done to them in the past 40 years or so, drawings or period photos are a more reliable source if you are wanting to model something specific within a certain time frame.

 

A broad rule of thumb anyway.

 

Very few have had new or radically altered boilers. They have repairs, not alterations.