What were the differences between the Gresley A1 and A3?

[razourlight962]

What are the main differences between the Gresley A1 and A3? I've been wondering for a while.

 

[30907]

http://www.lner.info/locos/A/a1a3a10.shtml#

The A3 was a modification of the original A1 design, and all of the surviving A1s were eventually rebuilt as A3s. Thompson designated the remaining members of the A1 class awaiting rebuilding as the A10 Class....

...Locomotives with the boiler rebuild were given the designation of Class A3.

Result of 30 seconds on Google.

 

[Sunbird24]

http://www.lner.info/locos/A/a1a3a10.shtml

Result of 30 seconds on Google.

This article is sadly lacking in one aspect of information.
After conversion of Great Northern to class A1/1 Peppercorn further developed the A1/1 for new construction. The new class became A1 and a further 49 A1's were built.
See here: http://www.lner.info/locos/A/a1peppercorn.shtml for details of what became known as the Peppercorn A1's. This web page details the history of all the LNER Pacifics via its various links.

 

[30907]

This article is sadly lacking in one aspect of information.
After conversion of Great Northern to class A1/1 Peppercorn further developed the A1/1 for new construction. The new class became A1 and a further 49 A1's were built.
See here: http://www.lner.info/locos/A/a1peppercorn.shtml for details of what became known as the Peppercorn A1's. This web page details the history of all the LNER Pacifics via its various links.

True, but it answers the OP's question about Gresley Pacifics.

 

[edwin_m]

And there's an article elsewhere on the site about Peppercorn A1s.

 

[MarkyT]

For those interested in comparing the characteristics of LNER pacifics (rather than Meerkats say - I'll get my coat!) I have a set of relevant locomotive and boiler diagrams here :

http://www.townend.me/files/drawings - lner pacifics/

These appeared in my father's latest book, LNER Pacifics Remembered, published by Irwell Press and available here (shameless plug) :

http://www.irwellpress.com/acatalog/LONDON_NORTH_EASTERN_RAILWAY.html#a681

 

[Sunbird24]

And there's an article elsewhere on the site about Peppercorn A1s.

Indeed, I even put the link in my original post had you cared to read it all and take it in!
My point is, that there will be many youngsters around now, and some not so young, who do not realise that the LNER had 2 very different class A1 pacifics during its 25 year life even though one was the same locomotive, albeit very different from the new builds of the late 1940s.

To add a little more relevant info as a timeline:
1922-1924 - Gresley built 52 A1 locomotives.
1927/8 - Gresley rebuilt 5 A1s to A3.
1928 - Gresley started new build A3s. 27 had been built by 12/1935.
1939 - Rebuilding of remaining A1s to A3 standard commenced.
1941 - Thompson took over from Gresley.
1945 - Thompson rebuilt one A1 to A1/1
1945 - Thompson redesignated remaining unrebuilt A1s as A10.
1945-1948 - remaining A10s rebuilt to A3 standard. A3 total now 78.
1946 - Peppercorn took over design work for new build A-1s.
1948/9 - Peppercorn built 49 new A1 locomotives.

A big thank you to MarkyT for providing links to the drawings of the various locomotives.

 

[w0033944]

I'm rather embarrassed to say that, despite being an LNER enthusiast, I'd never come across the Great Northern rebuild being described as an A1/1 before - I'd only ever seen it treated as a one-off which didn't require a class identity!

 

[Taunton]

Just to round this up in one place, the main difference between A1 and A3 was the replacement of the 180 psi boiler with a 220 psi boiler. The locos already built were converted (over many years) while there were also new ones built after the start of the conversions.

As well as the new boiler there were a range of other modifications, one of which was the reduction of cylinder diameter by 1 inch. This seems contrary to the increase of power the new boiler provided, but I am guessing the old cylinder walls were insufficiently thick to handle the increased pressure. I don't know whether they just had liners inserted or whether fully new cylinders were cast.

A 180 psi boiler was rather low pressure for an express loco when the first was built in the early 1920s - the GWR had 225 psi boilers on their Star class some 15 years beforehand. Any ideas why Gresley didn't go for a higher pressure from the start?

 

[jonty14]

http://www.lner.info/locos/A/a1a3a10.shtml#


Result of 30 seconds on Google.

If we all used Google for our answers there would be no point in this forum. Plus Google does not provide discussion.

 

[MarkyT]

Just to round this up in one place, the main difference between A1 and A3 was the replacement of the 180 psi boiler with a 220 psi boiler. The locos already built were converted (over many years) while there were also new ones built after the start of the conversions.

As well as the new boiler there were a range of other modifications, one of which was the reduction of cylinder diameter by 1 inch. This seems contrary to the increase of power the new boiler provided, but I am guessing the old cylinder walls were insufficiently thick to handle the increased pressure. I don't know whether they just had liners inserted or whether fully new cylinders were cast.

A 180 psi boiler was rather low pressure for an express loco when the first was built in the early 1920s - the GWR had 225 psi boilers on their Star class some 15 years beforehand. Any ideas why Gresley didn't go for a higher pressure from the start?

The reasoning for sticking with the lower pressure for so long was, as is often the case, cost. Experience had shown maintenance costs rose significantly with higher pressure with more remedial work being required when each boiler was overhauled periodically at Doncaster works. I guess it was only when those costs had been controlled, by a better understanding of metallurgy, design tweaks and greater precision in manufacture perhaps, and other means such as improved water treatment at depots, that it became economical to raise the pressure for new boilers to 220 psi with the Boiler No.94 design. With the higher pressure, the cylinder size had to be reduced to keep the maximum power output of the engine within the capabilities of the remainder of the mechanical components which had not changed. It was only with the later development of the A4 that thicker frames and larger rods and bearings were introduced to allow an increase in power. Later, A4 boilers to the Boiler No. 107 design, with their identical overall dimensions but an even higher design pressure of 250 psi, were the only boilers built new for Gresley pacifics. They were fitted to many A3s at overhaul throughout the 1940s and 50s, although their safety valves and maximum gauge pressures were limited in that case to 220psi.

 

[70014IronDuke]

The reasoning for sticking with the lower pressure for so long was, as is often the case, cost. Experience had shown maintenance costs rose significantly with higher pressure with more remedial work being required when each boiler was overhauled periodically at Doncaster works. ..... .

Which then, if true, begs the question: why did the GWR not reduce the BP of Stars and Castles - at least until the maintenance issues you bring up were sorted out?

I'm sure you are correct, but the higher BP will surely mean higher thermal efficiency - in other words, you will get more energy transferred to the train per pound of coal burned - other things being equal.

So you may have higher maintenance costs, but you will have lower coal consumption, and/or heavier trains hauled and/or faster haulage, even if your boiler needs more work on overhaul. (or shorter periods between overhauls).

The trick must have been to get the best combination, I suppose.

Interesting discussion though. Thanks for raising the questions.

 

[MarkyT]

Which then, if true, begs the question: why did the GWR not reduce the BP of Stars and Castles - at least until the maintenance issues you bring up were sorted out?

I'm sure you are correct, but the higher BP will surely mean higher thermal efficiency - in other words, you will get more energy transferred to the train per pound of coal burned - other things being equal.

So you may have higher maintenance costs, but you will have lower coal consumption, and/or heavier trains hauled and/or faster haulage, even if your boiler needs more work on overhaul. (or shorter periods between overhauls).

The trick must have been to get the best combination, I suppose.

Interesting discussion though. Thanks for raising the questions.

Perhaps at the time Swindon simply had more talented boilersmiths! Maybe the GWR water was better for boilers, and their generally excellent Welsh coal might also have made a difference to boiler life and repair costs.

All railways incrementally increased BP as they replaced and modernised their fleets because it was very desirable for the reasons you describe. The precise relative timings particular pressures were achieved by the different companies were probably subject to a lot of variables. 180 psi does seem particularly low for the time though. Perhaps there was always a conscious intention to uprate the locos later right from the beginning but only after exhaustive service proving at the lower risk lower pressure.

 

[edwin_m]

Maybe something to do with the GWR having 4-6-0s instead of Pacifics so needing to get a bit more out of them?

 

[Taunton]

Maybe something to do with the GWR having 4-6-0s instead of Pacifics so needing to get a bit more out of them?

or less ...

The GWR's lone Pacific showed that a key advantage of the 4-6-0, which after all has the same powered wheels and thus tractive effort, all other things being equal, is the absence of the rear trailing wheel. This means that when the loco pulls under load, given the relative position of the drawbar, there is a weight transfer to the rear of the loco, which is hence on a powered wheel, aiding adhesion, and not on a trailing one.

Anyone wanting to see a side by side comparison had only to go to Exeter St Davids in the early 1960s, to see departing from adjacent down platforms a Castle 4-6-0 with 12 on, no slip, and then a West Country 4-6-2 with about five on from Ilfracombe, WITH BANKER at the back for the climb up to Central, slipping on getting going, before it even crossed the Down Main to start on the hill.

In April 1925 the GWR lent 4079 Pendennis Castle to the LNER, who gave it 480 tons out of Kings Cross (must have been several coaches off the platform). Cecil J Allen, staunch LNER man, wrote that LNER management were "sniggering behind their hands" at what they contemplated on the climb to Finsbury Park. In fact the Castle, with Allen timing it, beat any known time by an LNER Pacific with such a load up the bank. I suspect the outcome was an uncomfortable meeting for Gresley with the LNER directors, and may have contributed to the A3 modifications that followed soon afterwards.

 

[edwin_m]

Following on from Taunton's logic suggests a 4-6-0 can make better use of its tractive effort due to having better adhesion, so there is probably more reason to give it a higher boiler pressure and/or larger cylinders.

However the Pacific can have a larger firebox because there is no need to fit a driving wheel under it, so other things being equal should be better producing large volumes of steam over a long period of time.

 

[70014IronDuke]

Following on from Taunton's logic suggests a 4-6-0 can make better use of its tractive effort due to having better adhesion, so there is probably more reason to give it a higher boiler pressure and/or larger cylinders.

However the Pacific can have a larger firebox because there is no need to fit a driving wheel under it, so other things being equal should be better producing large volumes of steam over a long period of time.

The 4-6-0 vs 4-6-2 argument here is a red herring when it comes to the issue of boiler pressure - why and why not the A1s originally had 180 psi.

The LMS and LNER needed the wider firebox because of longer journeys and, crucially, the quality of coal available meant that the grate became clinkered up towards the end of long trips.

The GWR used Welsh steam coal, and did not need the wide firebox. It's got nothing to do with boiler pressure.

EDIT "However the Pacific can have a larger firebox because there is no need to fit a driving wheel under it, ...."

Er, this is a*+e about face, if you'll forgive the expression. The designer would have loved to have put a driving axle under it (ie making it a 4-8-0). But he couldn't because he needed a wide firebox, and that necessitated the use of a trailing truck.

As someone else has pointed out, making it a 4-8-0 with a long, narrow firebox, was beyond the coal flinging skills of most able-bodied young firemen, at least for hours at a time.

THe SR concentrated the Lord Nelsons at Eastleigh-Bournemouth later on for this very reason, the were difficult to fire unless you got used to them.


xxxx

 

[MarkyT]

Following on from Taunton's logic suggests a 4-6-0 can make better use of its tractive effort due to having better adhesion, so there is probably more reason to give it a higher boiler pressure and/or larger cylinders.

However the Pacific can have a larger firebox because there is no need to fit a driving wheel under it, so other things being equal should be better producing large volumes of steam over a long period of time.

Yes even Stanier, a graduate of Swindon, used the longer frame and small trailing wheels of the Pacific form in his largest engines to provide a large wide firebox, and that form was also adopted by Bullied and the larger BR standards. Trailing truck designs with large fireboxes were also very common in Europe and the US, for instance: Prairie, Atlantic, Baltic, Mikado, Mountain. Smaller wheeled freight Decapods and similar could accommodate a wide firebox above the driving wheels. The GWR had better coal traditionally than other railways, so perhaps they could get more energy out of a smaller grate. You can create larger grate area by lengthening a firebox as an alternative to widening it but then you run into the difficulty of how far a human stoker can throw the coal into the front corners. Mechanical stokers became common in the later years of US steam, but it's interesting the designs almost all used a wide firebox form to gain the required large grate area for the largest boilers. I'm not criticising GW designs at all, but a King was probably at the limit of what could be achieved with a narrow firebox design, and was probably as big as the GW needed. Now think about what a modern exhaust system like a Kylchap or Lempor could have done for a King or a Duchess!

 

[Taunton]

Unfortunately for these propositions, and especially with apologies to 70014IronDuke (above), the use of WR-allocated Britannia 4-6-2s on the 1 in 36 South Devon banks was a nightmare, and eventually they were banned beyond Newton Abbot, some time after it was laid down that they MUST have an assisting loco between there and Plymouth, all due to slipping. They were put on the Cornish Riviera for a short while, to appease Riddles and his acolytes who sauntered over from 222 Marylebone Road to Paddington to see the "Rivvy" off at 1030 behind one, not knowing what the foreman at 83A had arranged. Doubtless an inspector strode forward to stand diplomatically between the long-suffering crew and "Mr Riddles, sir", especially on Tuesdays and Thursdays when it was a Laira turn.

Same experienced crews, same coal, same 4-hour-plus nonstop journey (with the big banks right at the end), and that Big Grate. Meanwhile, the Kings and Castles just carried on.

There was another 4-6-2 use on these banks for a (very) short while. Little known, but relevant today with discussions about the sustainability at Dawlish, is that there was a longstanding arrangement, going back way before WW2, that the GWR and the SR provided the loco and crews for one train a day on each others' routes between Exeter and Plymouth, to maintain route knowledge for crews in the event of a blockage of one another's lines. The Western normally provided a 43xx 2-6-0 via Okehampton, but the Southern started infiltrating West Country 4-6-2s once they had enough, and despite being on a short local train, these started coming to grief on the banks, until the Western told Exmouth Junction not to send them any longer, but to use an N class 2-6-0 instead.

 

[MarkyT]

Unfortunately for these propositions, and especially with apologies to 70014IronDuke (above), the use of WR-allocated Britannia 4-6-2s on the 1 in 36 South Devon banks was a nightmare,

This one didn't seem to be having too much of a problem on ten coaches climbing out of Paignton a few weeks ago (admittedly not quite as steep as Dainton)

https://youtu.be/pcbMcbAWpb8

 

[Taunton]

Nice sunny day, dry rail. Not always like that.

 

[70014IronDuke]

Unfortunately for these propositions, and especially with apologies to 70014IronDuke (above), the use of WR-allocated Britannia 4-6-2s on the 1 in 36 South Devon banks was a nightmare, and eventually they were banned beyond Newton Abbot, some time after it was laid down that they MUST have an assisting loco between there and Plymouth, all due to slipping. They were put on the Cornish Riviera for a short while, to appease Riddles and his acolytes who sauntered over from 222 Marylebone Road to Paddington to see the "Rivvy" off at 1030 behind one, not knowing what the foreman at 83A had arranged. Doubtless an inspector strode forward to stand diplomatically between the long-suffering crew and "Mr Riddles, sir", especially on Tuesdays and Thursdays when it was a Laira turn.

Same experienced crews, same coal, same 4-hour-plus nonstop journey (with the big banks right at the end), and that Big Grate. Meanwhile, the Kings and Castles just carried on.
...........

I know - or have read - that BR(W) * were not happy with the 7MTs, but I have never heard it reached such difficulties. What years are we talking about? (presumably 1954 or so?)

My only quibble would be - was this a revolt from the ground staff, as it were? I had a trip to Plymouth behind Tornado a few years back, and in all honesty I expected to have some slip on the banks. In fact, there was not one whiff of slip on the entire two-leg trip that I could detect (Bristol-Plymouth and back). Yes, it was a sunny, summer day.

* Canton seems to have been the exception. I gather they were used on Marches line trains successfully.

As to the Bulleids, well, I agree, they seemed to slip as standard procedure, at least in their original form. But again, I had never heard that the WR had banned them from this daily route knowledge turn.

xxxx

 

[Bevan Price]

Perhaps at the time Swindon simply had more talented boilersmiths! Maybe the GWR water was better for boilers, and their generally excellent Welsh coal might also have made a difference to boiler life and repair costs.

All railways incrementally increased BP as they replaced and modernised their fleets because it was very desirable for the reasons you describe. The precise relative timings particular pressures were achieved by the different companies were probably subject to a lot of variables. 180 psi does seem particularly low for the time though. Perhaps there was always a conscious intention to uprate the locos later right from the beginning but only after exhaustive service proving at the lower risk lower pressure.

For locos built in the 1910s up to the early 1920s, boiler pressures of around 175 to 180 psi were common on all UK railways. Only the GWR used 225 psi; the Midland Railway used 200 psi on some 4-4-0s.

Commenting on another point - although 4-6-0s had better adhesion characteristics than 4-6-2s, the extra wheel allowed longer fireboxes, and gave smoother running conditions. The LMS Royal Scots had a reputation for giving a very rough ride, especially at high speed - far worse than the Pacifics.

 

[30907]

As to the Bulleids, well, I agree, they seemed to slip as standard procedure, at least in their original form. But again, I had never heard that the WR had banned them from this daily route knowledge turn.

I think this may be the railway equivalent of urban myth.

The SR loco workings as late as 1957 (quoted in the Irwell Press volume on the Okehampton Line) list it as a WC diagram, and the unmodified ones didn't at first work West of Exeter. All the photos I've seen show one, except for a prewar shot of an N, and a reasonable load of 7 or 8. The WR workings via Okehampton were Moguls because nothing bigger was allowed across Meldon Viaduct.

 

[Taunton]

I really don't want to hijack what started off as an A3 thread, and I'll just mention in passing that I used to have a smudgy and juvenile box camera photo of Pegler's 4472, coming off an Ian Allan special at Taunton, no less, in 1963 http://www.sixbellsjunction.co.uk/60s/631019ia.html which might have been the first A3 through there since 4474 Victor Wild came through in 1925, returning the visit of Pendennis Castle to Kings Cross mentioned above. Goodness, more than 50 years ago.

Aside from the slipping, a further problem on Dainton bank, between Newton Abbot and Totnes, which you don't get elsewhere on the Lickey, up from Glasgow Queen Street, or going up to Exeter Central, is that at the top you go very abruptly from 1 in 36 up to the same going down. The longer boiler of the 4-6-2 exacerbated what even the crews of the shorter and more compact Western 4-6-0s had to watch carefully, that you needed to come over the summit still with a good level of water in the boiler, notwithstanding the huge effort going up, because otherwise the water level would tip forward too much and you risked exposing and dropping a fusible plug in the firebox.

Regarding the Bulleid's slipping, I can only record my first ever trip behind one, must have been about 1961, just before they were swept away from Dover boat trains by electrification, en route to a family holiday in Ostend, delayed by the loco slipping to a stand climbing out of Victoria to Grosvenor Bridge, not really that steep, where we sat until the tank that had brought the ECS in was able to come up behind and give a shove.

Could Meldon Viaduct really take a West Country but nothing bigger than a 43xx from the Western? I had always thought that the reason for such a small loco being used was that sometimes the crews came down from Tavistock on the GW Launceston branch, by the connection put in during WW2, entering Plymouth from the east; this had been a further precaution against the Southern line into Plymouth passing the Devonport navy base being bombed.

 

[Bevan Price]

Another reason for GWR locos not being allowed on the SR Exeter - Plymouth route could be that their width was "out of guage".

Those GWR routes built as broad guage could always accept wider locos / loads than many non-GWR lines built as standard guage -- recall the problems encountered by the "Grange" on its way to Huddersfield, as has been discussed elsewhere.

The samr reason prevented the use of GWR Kings on ex-LMSR and ex-SR routes during the 1948 locomotive exchanges, and the Modified Hall could only be used on the GC main line.

 

[MarkyT]

Another reason for GWR locos not being allowed on the SR Exeter - Plymouth route could be that their width was "out of guage".

The larger GWR engines were very broad in the beam around the cylinders and front buffer-beam area, which could be particularly problematic with overhang on sharper curves through platforms on other railways, passing closely mounted lineside equipment such as ground signals, and for some types of bridge girders.

That suggests GWR platforms must have had greater stepping distance to the carriage traditionally than other railways to accomodate this. Any truth in this?

There was also a height issue with a King many years ago on its first preservation visit to Paddington. This was before remodelling and the ballast had been built up progressively over the years, such that whilst all modern rolling stock could pass through, the taller King lost its safety valve and cover to one of the massive road overbridges on the approach to the terminus!

 

[Taunton]

the taller King lost its safety valve and cover to one of the massive road overbridges on the approach to the terminus!

Good thing it was before the electrification then!

The larger GWR engines were very broad in the beam around the cylinders and front buffer-beam area, which could be particularly problematic with overhang on sharper curves through platforms on other railways, passing closely mounted lineside equipment such as ground signals, and for some types of bridge girders.

I can recall 4932 Hatherton Hall, a good old 83B Taunton stalwart, on Taunton shed with scrape marks down the left hand cylinder cover. They were apparently a regular feature up at Old Oak Common on locos which worked down the West London Line and were, in theory, passed for certain Southern lines. Meanwhile, back at Taunton, there was a special engineering spec for the Barnstaple-Ilfracombe line to accommodate the 43xx which regularly worked over a Southern-maintained line.

About 1/2 mile west of Taunton station there was a wonderful footbridge over the line (only very recently replaced), where, it must have been 1961-2, last year of the Kings, you could stand right on top as they blasted out full regulator and well linked up getting a good run at Wellington bank. I tell you, from the vibrations I still recall, the chimney must have passed just a few inches underneath the footway, and it's a wonder they never blew the paving slabs up into the air. I wonder what the blast was like when they were still single chimney.

 

[Clarence Yard]

The King lost it's safety valve at Royal Oak because of the Paddington remodelling. The track was raised during the day and when it came back the safety valve bonnet was ripped off and the safety valve sheared. The resultant escape of steam so alarmed one of the well heeled nearby residents that the bomb squad was called out, which complicated the situation somewhat.

As well as the King, two HST power cars had their exhaust shields taken right off and several others had scores or dents. The following day I arrived for work at OOC and the Factory had the King in ready for examination.

The civils, naturally, had to pay for the lot.

 

[MarkyT]

The King lost it's safety valve at Royal Oak because of the Paddington remodelling. The track was raised during the day and when it came back the safety valve bonnet was ripped off and the safety valve sheared. The resultant escape of steam so alarmed one of the well heeled nearby residents that the bomb squad was called out, which complicated the situation somewhat.

As well as the King, two HST power cars had their exhaust shields taken right off and several others had scores or dents. The following day I arrived for work at OOC and the Factory had the King in ready for examination.

The civils, naturally, had to pay for the lot.

Thanks for the clarification. Was that preliminary track work getting ready for the remodelling because I don't recall any of the new signalling being in use at the time.