Does anyone know why the LNER persisted with parallel boilers when all the other three of the 'big 'four' had switched to tapered boilers?
I know it's heresy to say this, but I've always thought classes like the B1s and K1s looked slightly old fashioned because of their boilers - but it probably didn't affect their performance. The difference isn't so noticeable on the Thompson and Peppercorn Pacifics.
I read somewhere that tapered boilers are thermally more efficient than parallel boilers because they concentrate the water at the firebox end. But I've also read that Thompson derided the need for 'fancy boilers' as the 100A design was such a good steamer.
Over to you technical guys!
PS: I think GW locos looked pretty quaint as well - but for different reasons!
Parallel versus tapered boilers
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Pyewipe Junction
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Pyewipe Junction
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Colombo
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The arguement in favour of taper boilers goes something like this:
The hot products of combustion, the hot gases if you like, are at their hottest nearest the fire, naturally enough, and cool down as they proceed down the fire tubes. Most of the evaporation of water into steam takes place where the gases are hottest as heat is transferred through the steel boiler tubes faster in proportion to the greater temperature difference. As a result most of the steam will be evolved closest to the fire box and so you need to provide plenty of steam space there to prevent priming. This is also where you put the dome in which the steam is collected.
It is not necessary to have so much steam space towards the front of the boiler and so it is economical to taper the boiler downwards towards the front. This reduces the weight of the boiler in terms of the steel and the water not being carried about. Any saving of weight is a benefit, because this effects the rate of acceleration of the loco and train and so the fuel consumption. The civil engineers like a lighter loco on their overbridges and so do the permanent way engineers. Lighter weight increases route availability.
The cylinder block and the superheater elements in a modern loco are particularly heavy and when these latter were added to the general design it necessitated the addition of a pony truck to carry the extra weight at the front and so the 0-6-0 tender engine evolved into the 2-6-0 mogul. The taper boiler is lighter at the front end than a parallel boiler so this helps.
Some parallel boiler LNER designs came out too heavy as built and had to have lightening holes cut in the frames, thus creating weaknesses.
The fact that Thompson refused to fit taper boilers is of interest. The GWR and the LMS were sold on the principle and all the smaller BR Standards had them, these being derived from GW and LMS designs of course.
Colombo
The hot products of combustion, the hot gases if you like, are at their hottest nearest the fire, naturally enough, and cool down as they proceed down the fire tubes. Most of the evaporation of water into steam takes place where the gases are hottest as heat is transferred through the steel boiler tubes faster in proportion to the greater temperature difference. As a result most of the steam will be evolved closest to the fire box and so you need to provide plenty of steam space there to prevent priming. This is also where you put the dome in which the steam is collected.
It is not necessary to have so much steam space towards the front of the boiler and so it is economical to taper the boiler downwards towards the front. This reduces the weight of the boiler in terms of the steel and the water not being carried about. Any saving of weight is a benefit, because this effects the rate of acceleration of the loco and train and so the fuel consumption. The civil engineers like a lighter loco on their overbridges and so do the permanent way engineers. Lighter weight increases route availability.
The cylinder block and the superheater elements in a modern loco are particularly heavy and when these latter were added to the general design it necessitated the addition of a pony truck to carry the extra weight at the front and so the 0-6-0 tender engine evolved into the 2-6-0 mogul. The taper boiler is lighter at the front end than a parallel boiler so this helps.
Some parallel boiler LNER designs came out too heavy as built and had to have lightening holes cut in the frames, thus creating weaknesses.
The fact that Thompson refused to fit taper boilers is of interest. The GWR and the LMS were sold on the principle and all the smaller BR Standards had them, these being derived from GW and LMS designs of course.
Colombo
I seem to remember reading that Gresley claimed that the boilers on the A1/3/4 and V2/4's were actually coned not tapered. The original reasoning behind the coned boilers was to be able to fit the maximum diameter boiler possible within the LNER loading gauge.
Look at any GWR/LMS engine with a tapered boiler and you will see that the bottom of the boiler runs parallel with the running plate, Gresley's loco's boilers didn't.
Probably the best visual reference to Gresley's boilers would be the P1 class as the boiler was mounted high above the frames. Side on you can clearly see that the bottom of the boiler does not run parallel with the frames.
Look at any GWR/LMS engine with a tapered boiler and you will see that the bottom of the boiler runs parallel with the running plate, Gresley's loco's boilers didn't.
Probably the best visual reference to Gresley's boilers would be the P1 class as the boiler was mounted high above the frames. Side on you can clearly see that the bottom of the boiler does not run parallel with the frames.
Steve
I was flicking through an old book I've got and thought I'd share this image of an A1 boiler.
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Steve
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richard
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And for a reference on the relative thermodynamic benefits of a tapered boiler, note that Riddles decided to drop the tapered boiler when modifying the Stanier 8F into the WD Austerity.
Ie. the thermodynamic improvement was considered less important than cost and construction time.
Richard
Ie. the thermodynamic improvement was considered less important than cost and construction time.
Richard
Richard Marsden
LNER Encyclopedia
LNER Encyclopedia
Re: Parallel versus tapered boilers
In addition to improved steaming and reduced weight over the cylinders, tapered boilers also fooered benefit from reduced "sloshing" and henced reduced risk of uncoverint the firebox crown during breaking and decending gradients. They also improved visibility for the footplate crew.
Re: Parallel versus tapered boilers
Thompson's L1 was designed with a taper boiler but Thompson made it clear he was having none of it. Interesting observation by Richard on the Austerities. They had an LNER look about them and were good steamers. LMS 2-6-4T's they were much of a sameness regardless of whether they be Fowler with parallel boiler or Stanier/Fairburn/Riddles variants.
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Atlantic 3279
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Re: Parallel versus tapered boilers
Translation please?????u300878 wrote:fooered
Let's not overlook the fact that some LNER boilers with parallel outer clothing actually had slightly coned barrels, one version of the K4 boiler and certain later replacements for older "two telescopic ring" boilers being examples of this misleading combination of geometries.
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Re: Parallel versus tapered boilers
Does the taper boiler with Belpaire firebox offer any reliability advantages? After Tornados stay problems I noticed these problems do not seem to have affected the two Stanier pacifics currently running on the main line to the same extent. I think in the past couple of years they must they must have gone through as many "heating cooling cycles" or can it be down to just copper fireboxes?
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Saint Johnstoun
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Re: Parallel versus tapered boilers
Broken stays were a fact of life with all boilers after prolonged use and were replaced as a matter of course during boiler overhauls. Remember in the old days a locomotive like Tornado would have been shopped after a certain mileage, the boiler removed and sent off to be dealt with and usually another reconditioned boiler would be fitted before the locomotive shopping was complete.
For some reason, steel fireboxes were not favourite with most UK railways.
Another factor to take into account with Tornado is that this is effectively a new design of boiler, being all welded, although it is built to the dimensions of the original type. It may be that expansion and contraction characteristics have turned out to be somewhat different in reality to that expected in theory hence the stay problem.
For some reason, steel fireboxes were not favourite with most UK railways.
Another factor to take into account with Tornado is that this is effectively a new design of boiler, being all welded, although it is built to the dimensions of the original type. It may be that expansion and contraction characteristics have turned out to be somewhat different in reality to that expected in theory hence the stay problem.