Locomotive Boilers and Boiler Pressure

@S.A.C. Martin Some very intersesting points. Given that curved sections of metal withstand pressure better than flat surfaces, I wonder how that reflects in construction technique, staying arrangements and which has the greater bearing in regard to ongoing maintenance costs of otherwise similar boilers.

Woefully lacking in knowledge of LNER pracitses, I note the substantial difference in size between the original Holden S69 (B12/1) boiler and that of the Gresley/Thompson B12/3 rebuilds, but have no handle on whether ex-GCR reboilerings would allow better direct comparison of maintenence costs.

If records survive in Ireland, the ex-MGWR K Class (GSR/CIÉ G2/650) should provide a good indication, as class members ran with a mixture of interchangable round topped (saturated and superheated varieties) and Belpaire boilers. AIUI, all extant records are now in the care of the IRRS (http://www.irrs.ie) should anyone feel the need to investigate the matter in depth.

Edit: In light of Eightpot's post (below), I'd best add that taper boilers in the south were confined to GSR/CIÉ classes 305, 309/310,321/332 and 333 as built and all were replaced with parallel boilers. A vanishingly rare example of a locomotive policy actually being applied across the board!

 

Agreed, but one difference hasn't been commented upon as yet. The Belpaire boilers that the LNER had as fitted to GC and GE locos all had parallel barrels and outer firebox wrappers. To suddenly have to build boilers with not only taper barrels, but also outer firebox wrappers (and inner fireboxes too) that not only sloped down front to back, but tapered in along the sides as well, must have caused some headaches for those actually making this type for the first time. I think it was Thompson who stated that this type (8F) boiler cost something in the region of 70% more than an equivalent parallel round-topped firebox type.

This extra time and cost involved was presumably a factor noted by Riddles as the WD 2-8-0s and 2-10-0s came out with parallel and round-topped boilers.

 

Yes, Ive heard that before. The WD 2-8-0 was basically a cheapened and more basic version of an 8F

 

.... but still looked well enough in unlined BR black, when clean!

 

NOOOO! Don't get him started...

Oh no, too late...

 

Martin, do you really think of doing things like that? Shame on you.

Paul H

 

Sorry.

 

I only ever remember seeing some of 26D's allocation of them, in a VERY dirty state

 

In pretty much every shot I've seen from their service days they were absolutely filthy. The first time I saw one looking presentable was ex-SJ "90733" in preservation. Not exactly a typical example of the breed, I'll grant you, but ..... who cares?

 

That one looks superb, a fantastic job by the KWVR on another one of my favourite loco classes

 

? Is there anything similar apart from the whistle?

 

Smokebox ? wheel arrangement perhaps ?

 

The design was derived from it, proportions, etc, designed to do the same job, but much cheaper to build

 

Side stepping the 8f vs WD , what were the most powerful of the Atlantic's it would be interesting to compare each designers loco, for instance i would imagine the brighton engines would be very simular to the LNER ones

 

I suspect the ex-LBSC, ones once BP was increased, but I'd put money on nothing here coming remotely close to the Milwaukee RR 'A Class' (Image credited to coffeeasap.com):

 

Or the Pennsylvania E6.

 

Hell's donkeys ..... I think you're right. They're monsters!

 

Marsh certainly wasn't alone in applying a popular notion that superheated locos could utilise lower boiler pressure than otherwise similar saturated locos. It was pretty common over on the GS&WR too. Whether the reasoning was fuel economy, maintenence savings or a combination of both seems moot, as the idea seems to have died a natural death by the 20's in any event.

 

Also tangential, sorry, but...
I understand Stanier's firebox/boiler designs (i.e. Swindon!) were found to be cheaper to maintain than parallel boilers with round-topped or belpaire fireboxes because e.g. their stays lasted longer. Certainly the LMS accountants thought they were worth the money - after checking the sums.

 

This from raising steam on the LMS by A. F. Cook. Certainly the narrow firebox Stanier boilers come our well especially when compared with their similar ones on the GWR 'Hall' and 28XX 2-8-0s. The LNER 100A boiler better than the comparable GWR types. Note also the variation between the same (100A) and similar (5MT and 8F) boiler when divided between passenger and freight locos.

However, when it comes to the wide firebox types the list is headed by the SR Bullied and LNER A1 and A2 Pacifics with the 'Duchess' right at the bottom.