Disposal: Throw the fire out or leave in the box...?

I was wondering whether somebody could advise me as to why some railways throw the fire (or at least part of the fire) out of the box during disposal rather than leaving the fire to die off in the box and then raking it through to the ashpan before the loco is next lit up? The reasoning I've always been given as to why the fire is left in (such as is done on the GCRN) is that it slows down the cooling process of the box and thus reduces the stresses of cooling on the inner firebox metals, so if this is true doesn't that mean the converse argument of removing the fire means the cooling process happens at a faster rate and thus increases the stresses on the metal? I can understand the advantage if the loco has a few hours layover after a sustained period in action (as might happen to a SVR loco during one of their big galas with night-time running) and one needs to remove clinker which has built up, but I can't see a reason to throw the whole thing out of the loco isn't needed back in traffic til the next morning, or next week. Of course, it may be that railways don't ever throw the entire fire out, and I am happy to be corrected on that matter. So, any wisdom?

 

WSR policy is to bring the locos on shed in the evening & do the disposal in the morning.
That does mean that the loco needs to be able to be left in a state that when the boiler has been filled, it will make no additional steam and particularly will not blow off.
Getting that right takes some skill/experience.
If there is a possibility of clinker a bar might be run through the fire to lift that whilst still hot.
Otherwise the work is left for the morning when things will be at their coolest, all the heat paid for has been used, and the boiler will have cooled gradually so that there is still about 40psi on the clock when the morning crew book on at 6.00 am. With just over 3 hours to going off shed there is plenty of time for disposal, relight, steam raising etc etc.

 

I think everyone does. The water isn't cold.

 

A competent crew come on shed with the boiler already over 3/4 full so that there is not a large amount to be added.

 

Its has been known that at some railways the fire is cleaned of clinker etc and then fresh coal added and blacked out fire to slowly burn over night and keep loco hot.

 

That sounds basically the same as our practice - we'll throw the smokebox char out at night, but we leave the fire in and dispose in the morning before lighting up. We would normally clean the fire last thing, especially if there was a suspicion of clinker. We’ll also check ashpans (and if necessary clear) at night if they look full, particularly on small locos.

Tom

 

The way i used to do it was to come on shed with a full glass, blow down half a glass, run the fire through with the dart, remove clinker etc, clean the smokebox build the fire under the arch close ashpan dampers and doors top up water gently to bring pressure down to about 100 psi, and leave the engine with a full boiler
With everything shut off the fire will slowly die but the firebox will retain its heat then the following morning the next crew will drop or empty the ashpan after dropping the remains of the fire into the ashpan check the grate for missing bars, and the inner firebox for signs of leaks, then lay a new fire, i would never lay a fire using what was left unless it had been in steam overnight, then i would rake out one half lay a new fire, drop the other half using a few lit coals to keep it alive then spread the fire round the entire box .