Model Railway Forum

Hello All: I am new to the forum so I ask for your indulgence. I am asking this question on behalf of my eldest brother. The question is why did the GWR use the tapered boiler design for their Castle Class (hope I got that right) steam locomotives? What advantages did it have over the more commonly used parallel boiler design? Thank you.

Old Fat Robert

Just about all GWR locos had tapered boilers. Here is a quote.

"In addition to improved steaming and reduced weight over the cylinders, tapered boilers also added the benefit from reduced "sloshing" and henced reduced risk of uncovering the firebox crown during breaking and decending gradients. They also improved visibility for the footplate crew."

The Great Western Railway directors often travelled the world if they heard of a new design and they would then test them on their locomotives or on occasions, would test them by buying a complete locomotive from abroad (E.g. the De-Glens when the GWR tried out compounding). They would then experiment to see if the new designs were a success or not.
One of the GWR board of directors travelled to Canada many years ago as they heard of a boiler design which prevented boiler explosions should a steam locomotive hit a snowdrift, as the Canadiand were faced with a problem. When a locomotive hit a snowdrift, they would often de-rail where the weight of the front of the locomotive would plough itself downwards and come to a halt. The problem then was that the whole of the firebox was heating air rather then water and they had a fair few boiler explosions as the safety valves were unable to cope with this sudden expansion of heated air.
The Canadians found a rather clever solution to address this problem, and the GWR who were and always were a safety concious railway heard about it, and had to take a look.
The Canadians had tapered their boilers so that there was always water next to the firebox (Unless the loco came to rest at a very deep angle!) and so they were able to prevent boiler expolsions when faced with such a scinario.
So impressed were the GWR that from that point onwards, all their locomotive designs had "Swindon" boliers made to the Canadian tapered design.

Question answered I reckon MG.

It is a good question to answer. What puzzled me is why the railway companies that operated in Scotland did not follow the same idea?

Just want to take a moment to thank you all for your replies.

Old Fat Robert

It is worth adding that when the GWR showed the advantages of a taper boiler, all the other UK companies adopted it for new construction. Stanier served in Swindon so when he became CME of the LMS it was adopted as standard for all his main classes, and he rebuilt quite a few Fowler designs with it. The Southern were somewhat slower to adopt it although Maunsell fitted it to his Moguls and eventually Bulleid used it on his. Gresley of the LNER only adopted a taper boiler for his Pacifics, and it was not so pronounced as on other lines. Gresley also persevered with a round top firebox. Smaller sized LNER classes continued to have parallel boilers and Thompson continued to do so for his B1 class. Riddles of course adopted tapered boilers for all BR Standard classes.

The tapered boiler barrel is less easy to produce but the operating advantages are worth while.

LC&DR wrote: ↑Fri Feb 05, 2021 6:59 am It is worth adding that when the GWR showed the advantages of a taper boiler, all the other UK companies adopted it for new construction. Stanier served in Swindon so when he became CME of the LMS it was adopted as standard for all his main classes, and he rebuilt quite a few Fowler designs with it. The Southern were somewhat slower to adopt it although Maunsell fitted it to his Moguls and eventually Bulleid used it on his. Gresley of the LNER only adopted a taper boiler for his Pacifics, and it was not so pronounced as on other lines. Gresley also persevered with a round top firebox. Smaller sized LNER classes continued to have parallel boilers and Thompson continued to do so for his B1 class. Riddles of course adopted tapered boilers for all BR Standard classes.

The tapered boiler barrel is less easy to produce but the operating advantages are worth while.

They add considerable expense to production and I suspect the perpetually cash strapped LNER thought the benefits not worth the money.

I'm afraid the Canadian snow drift/boiler explosion explanation looks like a bit of an urban myth. The GWR and others wouldn't have bothered with the extra expense of a tapered or conical boiler just in the rare case of derailment. There was, however, a serious thermal benefit to be gained from a tapered boiler, which maximised the space for generating steam in the area of the firebox, which was the hottest spot. Earlier raised fireboxes, and the Belpaire design had similar advantages. The tapering allowed for a taller chimney within the loading gauge, with steaming benefits, and the lighter weight of the smaller diameter smokebox and front boiler section had certain advantages with regard to limiting the weight carried by the front wheels, so working best with the GWR's passenger locos with front bogies, Bulldogs, Cities, Stars, Saints, Halls, Castles, Kings, Manors, Granges and Counties of both varieties. Marginally less useful on the goods locos, both tender and tank.
Presumably the large scale production of tapered boilers at Swindon made them more cost effective, as the tooling was more expensive to prepare, which probably accounts for the limited take up of the concept on other lines.
The Taff Vale Railway did introduce a class of three 0-6-0 tanks with conical boilers in 1884 to operate on the Pwllyrhebog Incline, the larger section over the firebox would have protected the firebox from being uncovered when being hauled up the 1 in 13 rope assisted incline.