Fireboxes and wheel arrangements

[rockershovel]

There are some long-running questions on here which never seem to come to any useful conclusion... then you encounter some key detail which seems to break the logjam.

 

”why was the 9F designed as a 2-10-0, not a 2-8-2” seems to be a favourite. There’s a realer one about why a 4-6-4, or 2-8-4 is superior to a 4-6-2 or 2-8-2

 

there was a comment recently, that on a Royal Scot, the Crown sheet generated 70% of the steam raised, with the tube bank only raising around 10%. NOW we’re getting somewhere, because that means that given a sufficient quality of fuel, the volume of the firebox, and the presence of a combustion chamber, are more important than the grate area (given that the grate is not artificially constrained, relative to the firebox overall dimensions). It would also imply that a 2-8-2 has no real advantage over a 2-10-0 - provided that the driving wheels are small enough to fit under the firebox, and that the permanent way is if a sufficient standard. 

 

So American conditions favour the 2-8-2, because fuel quality is often variable to low, and the superior stability of the trailing truck is valuable; but the 2-10-0 provides better adhesion in British conditions.

 

it also demonstrates the old saw about the maximum useful length of a boiler being about 21ft, but fireboxes can usefully be made much bigger. 

 

 

 

[LMS2968]

Grate area becomes a factor at high outputs: you can get only so much heat per square foot. The argument that the wide firebox was fine provided it fits over the coupled wheels works well enough at the start of a trip but after several hours on the road, steam begins to deteriorate as the necessarily shallow ashpan becomes full and restricts the admission of primary air. In the book 'Steam Locomotive Casualty Reports'* Stephen Mourton instances several failures of 9Fs on arrival at Gloucester; all that was needed was to empty the ashpan.

 

The 9F was originally to be a 2-8-2 until Robert Riddles shoved his oar in. Whether or not it would have been a better loco we will never know. Although there are sometimes suggestions of building one, even if it materialised it will not be used on the sort of traffic where any advantage or disadvantage would become apparent.

 

*Runpast Publishing (2005) ISBN 1 870754 62 X

[rockershovel]

..... more instructive detail.

 

but, we CAN say that LNER experience showed that 2-8-2 types, heavier than the 9F 2-10-0 and capable of handling traffic loads in excess of the available traffic, were possible (but not necessarily desirable)... which taken in conjunction with the above comments about the ash pan capacity, suggests that either would have been a viable option, and we cannot know at this stage, why the decision was taken to concentrate on the 2-10-0 type. 

[rogerzilla]

There are practical considerations of heat affecting the rear wheel bearings which may dictate one layout over another.  A 9F has a smaller diameter boiler and shallow firebox compared to one of Gresley's finest, and the wheels are smaller, so the rear drivers don't have their oil smoked out by the hot firebox.

[The Stationmaster]

On 22/02/2020 at 12:04, rockershovel said:

..... more instructive detail.

 

but, we CAN say that LNER experience showed that 2-8-2 types, heavier than the 9F 2-10-0 and capable of handling traffic loads in excess of the available traffic, were possible (but not necessarily desirable)... which taken in conjunction with the above comments about the ash pan capacity, suggests that either would have been a viable option, and we cannot know at this stage, why the decision was taken to concentrate on the 2-10-0 type. 

There are two good reasons for avoiding a trailing carrying wheel if possible -

1. It can suffer unduly from ash etc coming from the firebox (e.g the GWR's Great Bear).

2.  Unless carefully countered with arrangements to shift the wheel loading it reduces the engine's adhesive weight as the back end of the engine 'sits down' on starting.

3,  It introduces increased complexity to the engine although that is not really a problem in engineering terms but don't forget a design aim with BR Standards was maximum simplicity.

 

There is one very good reason for using carrying wheels on a tender engine - it can help the design to incorporate a larger and wider firebox which in turn increases the engine's steam raising capacity (until the ashpan starts to choke the primary airflow).  US designs of very large locos using trailing trucks generally only ran, particularly on the largest designs, from one division point to the next (usually 100 miles)  before stopping for water and coaling and in some cases clearing ash below the firebox.

 

With any design capable of moving larger than normal loads, such as Gresley P1s (or the equally capable BR 9Fs),which could manage loads in excess of 1600 tons there is always a pay off between load, availability of traffic to make up that  maximum load, the speed at which said locomotive can move the maximum load it is capable of moving, and the ability of the infrastructure to accommodate such trains in the first place, and accommodate them on a mixed traffic railway.   In other words are very heavy loads are realistic operational prospect?  

 

Simple answer is 'often not'.  For example in a paper I presented to a symposium at the IMechE back in the early 1990s I illustrated the difference in loads which ever increasingly powerful locos had achieved on Mendip stone trains compared with the impact those increases had produced on running times and the sheer ability to find a path for increasingly heavier and slower trains.  You can simply add more power to reach a state where you cannot path the weight of load you are capable of moving.  Once the Class 59s had arrived we ran 5,000 ton (not tonne) trailing loads out of the Mendips with no problems but they were restricted to being run at certain times of day due to their slow speed.  But trains exceeding 4,000 tons are much less common nowadays because the traffic demand isn't there.

[Grovenor]

Quote

and we cannot know at this stage, why the decision was taken to concentrate on the 2-10-0 type. 

Well E.S.Cox explained it in considerable detail in his book on the BR Standards. And, as mentioned above it came down to Riddles' preference based on his experience with the WD 2-10-0s.

Rgds

[Miss Prism]

Good for continuous hill-climbing:

 

 

[Ohmisterporter]

IIRC whilst on a visit to South Africa Nigel Gresley said the Class 19D was one of the world's best locomotive designs. 

[rockershovel]

2 hours ago, Grovenor said:

Well E.S.Cox explained it in considerable detail in his book on the BR Standards. And, as mentioned above it came down to Riddles' preference based on his experience with the WD 2-10-0s.

Rgds

 

.... which brings it all together, really. LNER demonstrated that it was possible, but not particularly useful, to build a 100-ton loco capable of pulling more traffic than the network could usefully handle. LMS and GWR had demonstrated that the maximum useful size for a 2-8-0 was in the 72-75 ton range, and the 78 ton WD 2-10-0 supported that, also demonstrating that a ten-coupled loco was feasible under British conditions. 

 

The weight transfer issues relating to locos with a trailing axle were well established. 

 

So, the 90 ton 2-10-0 gives higher adhesive weight, maximises the useful size of the loco and leaves the possible disadvantage of restricted ashpan capacity, which would appear in service occasionally 

[LMS2968]

42 minutes ago, rockershovel said:

 

So, the 90 ton 2-10-0 gives higher adhesive weight, maximises the useful size of the loco and leaves the possible disadvantage of restricted ashpan capacity, which would appear in service occasionally 

'Occasionally' might be a bit optimistic, really. The latest engines, in this case the 9Fs, would be first choice for fast fitteds and long distance work, just the sort of jobs where the ashpan's capacity might be most tested.

[EddieB]

2 hours ago, Miss Prism said:

Good for continuous hill-climbing:

 

 

Built by Krupp, redesigned by Wardale, destroyed by metal thieves...

[Pandora]

I think it was Dr Tuplin who had an adverse opinion on the design of the 9F 2-10-0 firebox  and the rearmost driving wheelset

[DCB]

The discussion is interesting,  Big firebox, short barrel, combustion chamber, that's what Churchward tried around 1902 with the Kruegers.  That went well! most out of service after 2 years.   He then came up with the Great Bear.   That originally should have had a combustion chamber, but ended up with 23ft boiler barrel.  It was un successful, well it hauled over 1000 tons from Stoke Gifford to Acton at a good lick, sort of turn 9Fs could have done, it had 4 cylinders, a low tractive effort for its size around 27,000 lbs and a wide firebox, 40 sq ft, like a 9F ( or Brit)   No record of it ever falling apart in service, or shedding its tender.     The GW did work on boilers for express locos. See Power of the Castles and Kings,  Basically they found as boiler pressure was raised it made sense to shorten the barrel and increase the superheat.   The proposed short Castle boiler emerged in 1945 on the Counties but after 30 X 280 lbs Counties they reverted to 225 psi Castles. In theory that high pressure Castle would have out performed a King.

 

Ash pan capacity is interesting.  The GWR worked out if you use rubbish coal you need to burn more of it, and when you had to drag it from south wales to Lunnon or Penzance it made sense to use the god stuff.   That meant it burned cleaner and produced less ash. They used to run Penzance to Paddington 290 miles(?)  with one loco so the ashpans were ample for the usual 200 miles max daily duties.    If you want to use crap coal you need big ashpans, ( or just leave the ashpan off and use concrete sleepers)

 

The 9F was supposed to be a eight coupled Brittannia with a leading truck instead of a bogie.   With hindsight a 5ft 8" wheeled 2-8-2 with a Britannia boiler would have been  arguably a more useful beast, as would have been a 3 cylinder Britannia with Caprotti valves a la Duke of Gloucester with a Britannia and of course a 6MT Pacific with a Britannia boiler running at 225psi to reduce wear and propensity to slip.  I am pretty sure Robinson, Gresley or Churchward would have managed to do all 4 with one boiler, but hey LMS ruled and they couldn't even make one boiler to fit all the Black Fives.

There was no requirement for a 5ft wheel 2-10-0.  The GW toyed with a King Boilered 4ft 8" wheel 2-10-0 for the Ebbw Vale iron ore trains, the same ones the first 7 or so 9Fs were initially allocated to haul, traffic which they struggled with until someone bodged on Std class 4 regulator valves so they couldn't actually operate with more than about 60% regulator, not that it made any difference to anything.   The need was for fast heavy freight locos, the best of which were probably the GW 47XX with 4ft 7 ish driving wheels and a 65 mph top speed which stayed on fast freight duties from introduction in 1923 till withdrawal in 1964.

They had an unusually low tractive effort for such a large loco which made them very sure fitted.    With sensible weight distribution, 20 tons per driving axle and little on the trailing truck a 5ft 8" Britannia boilered  2-8-2 could have been a very useful tool.   Especially in Scotland, working the heavier passengers on the Highland main line in place of pairs of Black 5s and taking the heavy but easily timed sleeping car trains from Perth to Crewe  over Shap and Beattock in place of Stanier Pacifics, which could have been redeployed to the Midland main line. They would probably have run greater mileages than the 9Fs did between overhauls, as the 9Fs taste for speed and excessive piston, (or was it valve) ring wear which resulted from their use on fast , 60 mph plus trains.  

 

 

[Siberian Snooper]

5 hours ago, DavidCBroad said:

They used to run Penzance to Paddington 290 miles(?)  with one loco so the ashpans were ample for the usual 200 miles max daily duties

 

I think you will find that most trains changed locos at Plymouth, as trains were shortened heading into Cornwall and extended heading to Bristol or London. Other trains were split at Newton Abbot.

 

 

[DCB]

5 hours ago, Siberian Snooper said:

 

I think you will find that most trains changed locos at Plymouth, as trains were shortened heading into Cornwall and extended heading to Bristol or London. Other trains were split at Newton Abbot.

 

 

I know, but they ran an Exeter Saint to Penzance on day 1, Penzance to Paddington on the Up West of England Postal on day 2 and back to Exeter on day 3.  It changed crews at Exeter but it was done to claim the record for the longest through run. Obviously it was a bit pointless after the LMS ran to Edinburgh and Glasgow non stop as a stunt and the LNER ran London Edinburgh non stop daily in summer. 

I think it was done partly to give Exeter shed and crews some work as more trains split at Newton Abbott and Exeter's importance declined. 

 It did prove Saints could do 200 mile plus runs on fast heavy trains with no problems, and as an aside proved Stars could not.  When Stars went on to the they ran out of lubricating oil in the small end reservoir of the outside con rods as they approached London.   At least one broke a con rod at the small end as a result, which was no big deal with GWR slide bars, but would have been an almighty smash with BR/LNER type...

Collett immediately ordered an investigation and they revised the oil boxes on all the 4 cyl locos as a direct result. KJ Cook wrote about it in Swindon Steam.

I believe the trouble came from the short con rod moving through a greater angle than the longer 2 cyl rods as the 2 cyl locos didn't have the same issue.

Edited February 26, 2020 by DavidCBroad

[Reorte]

11 hours ago, DavidCBroad said:

( or just leave the ashpan off and use concrete sleepers)

 

That answers a bit I've been wondering all along about in this discussion - why not just let the ash fall out? Obvious really when you think about it that dropping hot ash on wooden sleepers impregnated with creosote isn't a great idea.

[LMS2968]

7 minutes ago, Reorte said:

 

That answers a bit I've been wondering all along about in this discussion - why not just let the ash fall out? Obvious really when you think about it that dropping hot ash on wooden sleepers impregnated with creosote isn't a great idea.

Although how you regulate the flow of primary air at times of low steam requirement then becomes an issue.

 

11 hours ago, DavidCBroad said:

I am pretty sure Robinson, Gresley or Churchward would have managed to do all 4 with one boiler, but hey LMS ruled and they couldn't even make one boiler to fit all the Black Fives.

No, the LMS came up with the strange idea that the boiler should fit the loco and not the other way around; and  when development showed that there was a better alternative to an existing design it should be adopted.

[The Stationmaster]

2 hours ago, DavidCBroad said:

I know, but they ran an Exeter Saint to Penzance on day 1, Penzance to Paddington on the Up West of England Postal on day 2 and back to Exeter on day 3.  It changed crews at Exeter but it was done to claim the record for the longest through run. Obviously it was a bit pointless after the LMS ran to Edinburgh and Glasgow non stop as a stunt and the LNER ran London Edinburgh non stop daily in summer. 

I think it was done partly to give Exeter shed and crews some work as more trains split at Newton Abbott and Exeter's importance declined. 

 It did prove Saints could do 200 mile plus runs on fast heavy trains with no problems, and as an aside proved Stars could not.  When Stars went on to the they ran out of lubricating oil in the small end reservoir of the outside con rods as they approached London.   At least one broke a con rod at the small end as a result, which was no big deal with GWR slide bars, but would have been an almighty smash with BR/LNER type...

Collett immediately ordered an investigation and they revised the oil boxes on all the 4 cyl locos as a direct result. KJ Cook wrote about it in Swindon Steam.

I believe the trouble came from the short con rod moving through a greater angle than the longer 2 cyl rods as the 2 cyl locos didn't have the same issue.

A number of people well familiar with Reading a long while back spoke often of The Great Bear suffering a hot box on the trailing carrying wheels on its return working from Bristol to Paddington (which was usually a fast goods at one time).

[jim.snowdon]

The only reason that Churchward had The Great Bear built was to gain experience with wide fireboxes, not to build an engine with even larger cylinders, and in that, he succeeded. The boiler, by all accounts, steamed quite well once the different firing technique had been mastered, and who knows what it might have led to had the First World War not intervened. As it was, Swindon's narrow firebox boilers were performing quite well. They didn't get improved until after the Second World War, with the work done by S O Ell that resulted in the changes to higher superheating.

 

Riddles took a quite conscious decision to avoid inside cylinders and all that went with them, and I don't think that there is any doubt that the Class 7s did all that was expected of them. Like all unequalised Pacifics, they could slip, and a 2-8-2 would have suffered similar as a result of weight transfer effects. It can't be said that hindsight proved him wrong in adopting the 2-10-0. And as for high speed running, it can't be said that the 9Fs were designed for it, only that it turned out that they were capable of it, and for the class as a whole, it didn't happen that often. The exploits of a few are better remembered than the more mundane activities of the rest.

 

Jim

[Happy Hippo]

4 hours ago, Reorte said:

 

That answers a bit I've been wondering all along about in this discussion - why not just let the ash fall out? Obvious really when you think about it that dropping hot ash on wooden sleepers impregnated with creosote isn't a great idea.

The ash pan floor also has an effect on the amount of air being drawn through the fire bars.  

 

With a 'sealed' unit you can control the air admission with the front and rear damper controls (dampers are simple flap like devices)

 

If you remove the ashpan then you cannot control the airflow through the fire and it would get very hot very quickly once working.  then the firebars would melt and your fire would be dumped all over the track.

 

(Just seen LMS 2968's reply.  apologies for duplication.)

[DCB]

1 hour ago, Happy Hippo said:

The ash pan floor also has an effect on the amount of air being drawn through the fire bars.  

 

With a 'sealed' unit you can control the air admission with the front and rear damper controls (dampers are simple flap like devices)

 

If you remove the ashpan then you cannot control the airflow through the fire and it would get very hot very quickly once working.  then the firebars would melt and your fire would be dumped all over the track.

 

(Just seen LMS 2968's reply.  apologies for duplication.)

The usual UK problem was insufficient air space through the dampers and fire grate.   Duke of Gloucester was a recent example but the dramatic one was the GWR Atlantics which would not steam. Churchward had Stanier compare the Arlantcs with the 4-6-0 and reported the only difference was the Ashpan.   The Atlantic had one set of dampers less.  Churchward ordered the Atlantics fitted with 4-6-0 ashpans.  

[LMS2968]

2 hours ago, Happy Hippo said:

(Just seen LMS 2968's reply.  apologies for duplication.)

No worries, a bit of confirmation is always welcome!

[Reorte]

15 hours ago, Happy Hippo said:

The ash pan floor also has an effect on the amount of air being drawn through the fire bars.  

 

With a 'sealed' unit you can control the air admission with the front and rear damper controls (dampers are simple flap like devices)

 

If you remove the ashpan then you cannot control the airflow through the fire and it would get very hot very quickly once working.  then the firebars would melt and your fire would be dumped all over the track.

 

(Just seen LMS 2968's reply.  apologies for duplication.)

I suppose I thought that it would build up if the dampers were shut but fall out into the ashpan if they were open, but it's also pretty obvious that it would still completely change the airflow.

[Trog]

On ‎26‎/‎02‎/‎2020 at 14:15, Reorte said:

 

That answers a bit I've been wondering all along about in this discussion - why not just let the ash fall out? Obvious really when you think about it that dropping hot ash on wooden sleepers impregnated with creosote isn't a great idea.

 

Fouling the ballast with ash is not all that clever either. Even back in the days when the Civil Engineer had an army of men available to shovel the ballast out and fork it back a bed at a time.

[LMS2968]

It should also be remembered that what drops hot out of the ashpan. even more so than what is ejected from the chimney, is likely to find its way into adjacent fields.