BR steam Power classification (F)

[DCB]

 I was wondering about Midland / LMS / BR Power classifications, as there doesn't seem to be an awful lot of logic as I understand on the S&D the LMS 4F was stronger than the BR Std 4MT  4-6-0 and  the 7F 5F West Countries, and LNWR 0-8-0s Originally had their cylinders linered down to stop wheel slip yet later had them restored and were uprated to 7 F from 6F despite not being able to start trains which were heavier.

 

I FOUND THIS

 

On 15/04/2017 at 18:07, asmay2002 said:

 

The BR power classifications were defined by calculation introduced in 1949.  The P classification was calculated thus:

 

Factor = (Free gas area through tube bank x grate area x tractive effort) divided by 10000.

 

The factors were grouped as follow:

 

1P from 0 to 65

2P 66-100

3P 101-180

4P 181-300

5P 301-420

6P 421-600

7P 601-900

8P over 900.

 

The regions were allowed to alter the classification from that which the calculation gave.  In the case of the King the factor comes out as 744 (i.e notionally only 7P)  and for the Castle about 450 (i.e 6P) depending on which version of the No8 boiler it had.  The rebuilt Scot comes out at  501 (also 6P).  The power classes were all altered upwards by the regions for these engines based on their experience and needs. On the other hand a Britannia comes out at 917 (i.e it would just scrape into class 8) - much less than the larger pacifics but higher than a King. Some of the Pacifics were well over 900, for example the LMS Duchess comes in at 1378, BR’s Duke at 1290 and the A1 at 1178.  For interest, the LNER W1 was at 1286 and the P2 at 1351, the A3 came in at 843 and the A4 at 909.   These numbers might explain why the 4-6-0s have often been disapointing in preservation on the main line with the BR era power classifications exagerating their capabilities compared to the Pacifics which in normal service would have been limited by the capability of the firemen. 

 

A while ago I did a spreadsheet to work out the numbers of a lot of classes for personal interest as there are some discrepancies between the calculated power classes and the numbers painted on the side of the locos.  It is also possible to run the numbers for designs that were never built or foreign locos. 

 

The “F” calculation is different and is based on Tractive effort and adhesion weight.

 

SO MY QUESTION IS how was that “F” calculation based on Tractive effort and adhesion weight calculated, and did it have any value?.

[Hal Nail]

1 hour ago, DCB said:

SO MY QUESTION IS how was that “F” calculation based on Tractive effort and adhesion weight calculated, and did it have any value?.

 

[LMS2968]

Theoretical ability for steam locomotion was always at best a guide as there are so many other variables. Free gas area through tube bank and grate area are fixed values, but the actual tractive effort varies with speed, and isn't calculable anyway but must be measured, hence the need for a dynamometer car. Factors to be considered are the ability to raise steam, the cylinders' ability to use that steam at different speed rates, and the wheels' adhesion with the rails. Free gas area and grate area do indeed have an effect on the steaming ability but so too does the draughting, not included above, and the type and proportions of the chimney and blast pipe arrangements. Then there is the quality of the coal and the fireman's ability at feeding it through the firehole, not to mention the state of blockage of the grate, firebars and amount of smokebox char. Then there is the degree of superheat. The cylinders' abilities vary with the type of valve gear, the valve travel, the ability of the steam to enter and leave the cylinders without restriction and the driver's skill in choosing the optimal combination of regulator and cut off are all further factors.

 

As an example, a diagram for the Midland / LMS 2Ps was to assist the Pacifics on the heavy overnight trains out of Euston. The Pacifics' drivers hated this: however useful the 2P was when climbing Camden Bank, once the train was into its stride the 2Ps' contribution diminished as speed rose to the point where the Pacifics were not only pulling the train unaided but actually pushing the 2Ps as well. The very constricted steam passages past the cylinders to the steam chests below did not allow the steam a free passage into and out of the cylinders.

 

Generally, shed foremen knew what a class of engine, and often what an individual engine within that class, could do and allocated accordingly.

[Aire Head]

6 hours ago, DCB said:

LMS 4F was stronger than the BR Std 4MT  4-6-0

 

4MT being different to 4F. Mixed traffic locos are capable of doing the work of "F" or "P" but aren't necessarily as good as them at doing it.

[DCB]

11 hours ago, LMS2968 said:

As an example, a diagram for the Midland / LMS 2Ps was to assist the Pacifics on the heavy overnight trains out of Euston. The Pacifics' drivers hated this: however useful the 2P was when climbing Camden Bank, once the train was into its stride the 2Ps' contribution diminished as speed rose to the point where the Pacifics were not only pulling the train unaided but actually pushing the 2Ps as well. The very constricted steam passages past the cylinders to the steam chests below did not allow the steam a free passage into and out of the cylinders.

Generally, shed foremen knew what a class of engine, and often what an individual engine within that class, could do and allocated accordingly.

Interesting, I wonder if the fact 2Ps had not been used regularly on express work on the WCML affected this, I wonder as they had Stephensons  link motion and short lap short travel valves if the drivers pulled them up too far on the reverser when a long cut off and nearly closed regulator might have achieved better results.

 

 

12 hours ago, Hal Nail said:

 

Thanks.  My Forum search didn't show this  one.

[The Johnster]

19 hours ago, LMS2968 said:

19 hours ago, LMS2968 said:

Generally, shed foremen knew what a class of engine, and often what an individual engine within that class, could do and allocated accordingly.

 

 

Exactly, and I suspect that the Western, Southern, and such parts of the other regions that had not previously been part of the LMS, largely ignored these nee-fangled ratings and carried on in time-honoured fasion anyway.  Actually, I don’t suspect, I know because I remember them doing it, the WR used it’s Alphabetic power class and coloured spot RA system despite the locos being given BR classifications.  A loco diagram would require, say, a blue C loco and the shed foreman allocated one that he knew had sufficient coal bunkerage and tankage to do the run, enough TE to start the load, and wheels big enough to time it.  The WTT gave amended timings and loads for engines with smaller wheels if and when needed (the principle being that any of the locos could haul any of the trains if they had to, which they did sometimes, hence the provision of vacuum brakes on all GW-designed locomotives except 67xx and 6750), which is why you found 28xx or 42xx adding to the delays on summer weekend reliefs to Devon and Cornwall, and 56xx thrashing along from Cardiff to Pontypool Road with Manchester  or Liverpool expresses, or 94xx on the up Cheltenham Flyer as far as Gloucester. The BR classifications were regarded as ‘Midland practice’, just as the BR Standards were regarded as ‘Midland engines’, rightly or wrongly.  
 

To a younger trainspotting Johnster, it made little sense that a 56xx equated to a Hall or a Black 5 (both were 5MT according to BR, and even according to the GW the 56xx and Hall were both Red D), and insane that a small prairie was the same (4MT) as a large one, or more to the point a 3-cylinder LMS 2-6-4T, and ‘twice as powerful’ as an Ivatt/Riddles 2MT small prairie or mogul.  Clearly there were differences in wheel and cylinder size that affected the classifications, and I was aware, because the driver of the Swansea Harbour Trust Peckett who gave me a cab ride and let me ring the bell told me, that it’s tractive effort was the same as a King’s, but it wasn’t anything I could get my head properly around, something I understood a bit but couldn’t answer questions about.  
 

Obviously, a 56xx couldn’t do Hall work, but a Hall could do 56xx work, passenger work anyway.   I’d seen LMS and BR Standard 2-6-4Ts hauling 10-coach trains to Glasgow at Largs and Ardrossan, and knew that a large prairie would have been completely out of it’s depth with them, never mind a small one, 4MT my *rse

 

Similarly, in steam days WR men ignored the BR power classes when referring to BR standard locos.  Britannias were ‘70 thousands’, never 7MTs, 5MTs were ‘73 thousands’ and so on.  Of course this followed on very naturally from the way they’ referred to GW classes, as did the TOPS classes.  BR Standards on the WR were given GW RA spots and alphabetic power classes, and WR diesels were given WR RA spots at least until the application of 1966 blue livery. 
 

I imagine similar continuations of previous practice occurred in other places that had not been on the LMS as well. 
 

21 hours ago, DCB said:

these numbers might explain why the 4-6-0s have often been disapointing in preservation on the main line with the BR era power classifications exagerating their capabilities compared to the Pacifics which in normal service would have been

I think we are back to the old 4-6-0 

=narrow firebox/pacific=wide issue counterbalanced by the ‘pacifics=light-footed’ one.  A wide firebox is a very useful thing to have with you if you need to raise and maintain steam pressure quickly enough to haul heavy 14-coach expresses at 90mph or so on a daily basis, but the pacific you need to carry it may not be the best tool for getting that train under way from rest. 
 

My childhood memories include watching Britannias setting off from Cardiff General with the up Red Dragon most Saturdays; 14 bogies unassisted from the bottom of the Severn Tunnel to Badninton.  There is a slight rise over the Canal Wharf bridge out of the General, then the SWML drops steeply to ground level beneath the CEJ (valley lines) bridge.  The Brit looked magnificent, obviously more powerful than a Castle because, well, look at the size of the beast, and the fireworks were very impressive!  Wheelslip, the fireman’s best efforts Vesuviused out the chimney, sand flying all over the place, set back and try to jerk them into action; it would take about 5 minutes, nearly a third of the booked running time to Newport, to get half the train over the bridge and on the downgrade, at which point the last coach was just clearing the platform.  A similar performance ensued at Newport, and if the load exceeded 14 there was assistance to be attached at STJ and removed at Stoke Gifford or Badminton.  
 

A Castle with a similar load also needed assistance, but when right away was given at Cardiff, the driver popped the whistle, put her into forward gear, and opened the regulator.  And that was it; the engine proceeded to pull the train over the bridge with no fuss or bother whatever the state of the rail, accelerating steadily.  So, the Brit lost time all the way to Badminton and had to thrash up to about 90, the high 80s at least, on the run in to London to make it up to arrive right time Paddington.  The fireman was kept hard at it all the way and needed the extra ton of coal his tender had over the Castle’s.   The Castle could time the train to Badminton (the timings were fairly generous), and not have to be thrashed to make it up on the rest of the journey,  but the fireman was extended to the limit on that long climb with the narrow firebox feeding four cylinders, and it was just as well that he had some respite after Badminton.  The Castle's bigger driving wheels lowered coal consumption so the extra ton wasn’t needed. 

A well-regarded 4-6-0 and a pacific with as good a boiler as any, ever, steam on a candle, each with strengths and weaknesses, both capable of running the train and arriving right time, but requiring different styles of driving and very different styles of firing to do so.   But the Castle was better at keeping to it’s booked times and path, which made life easier for Control and the signalmen.   The Brit had to play catchup, but it could…

 

 

 

Edited December 23, 2022 by The Johnster

[rogerzilla]

Don't forget that the old LMS 5X classification was changed to 6 by BR, meaning everything from 6 upwards had 1 added.  This means a 9F would possibly have been an 8F in LMS days, had it existed.  The Stanier 8F was a 7F initially.

Edited December 26, 2022 by rogerzilla

[LMS2968]

Where to classify an individual class could be problematic if simple formulae were followed. The Horwich Crab started life as 4 but this was soon changed to 5P4F as they could handle heavier trains than the Compounds, although still classed as only equal to the Derby 'Big Goods'. In 1938 the classification was again changed to 5P5F, although wartime brought them back to a simple 5F, no P classification. In BR days they were 5MT or just 5, but later reclassed for political purposes as 6P5F, thereby allowing them to work the heavier weekend excursion trains which otherwise required a Baby Scot or 5X Jubilee.

 

No theoretical bases involved, either tractive effort or boiler ratios, but the results of experience in traffic.

[AMJ]

From recolection the Crosti fitted BR 2-10-0 were classed as 8F rather than 9F

 

At the other end of the power range many shunting locos were classed as 0F such as the L&Y Pug

 

Theoretically the LMS & LNER Beyer-Garratt's should have been double digit power rating.

[Right Away]

Regarding freight power classifications, BR(SR) utilised an A or B suffix on certain locomotives denoting whether the braking performance was lower or higher respectively than that of a nominal F rating for that power.

For example a Q1 0-6-0 could pull a town away, however if that “town” was unfitted or with a limited fitted head, stopping it could be another thing entirely; hence a classification of 5FA. On the other hand, a Brighton K class Mogul was rated as 4P5FB denoting it having a braking ability superior to that of an engine of generic 5F power.

 

Bullied “Light Pacifics” with their 7P5FA classification were completely unsuited to unfitted work. Indeed it was reported that when on lightly loaded passenger workings weighing little more than the engine and tender, there could be considerable sparking throwing from the engines’ brake blocks, Hollywood fashion.

 

Edited December 26, 2022 by Right Away
correction

[asmay2002]

On 22/12/2022 at 04:56, DCB said:

 I was wondering about Midland / LMS / BR Power classifications, as there doesn't seem to be an awful lot of logic as I understand on the S&D the LMS 4F was stronger than the BR Std 4MT  4-6-0 and  the 7F 5F West Countries, and LNWR 0-8-0s Originally had their cylinders linered down to stop wheel slip yet later had them restored and were uprated to 7 F from 6F despite not being able to start trains which were heavier.

 

SO MY QUESTION IS how was that “F” calculation based on Tractive effort and adhesion weight calculated

As you were quoting my original post I better answer this.  The answer is very simply. The BR "F" classification took the lower of two figures, EITHER the tractive effort OR the adhesion weight in pounds divided by 4.5 and then fitted them into this table.

Class  

1     up to 15500

2    15500-19000

3    19000-23000

4    22500-26000

5    25500-28000

6    27500-30000

7    29500-32000

8    31500-35000

9    34500 and above

 

In some case poor brakes led to locos being put in a lower class than the numbers suggest.  The LMS used a different calculation.  (RCTS BR standard steam locos vol 5).

 

 

Edited December 26, 2022 by asmay2002

[The Johnster]

‘0F’ was called ‘unclassified’ on the WR, so therefore equivalent to the LMS Beyer-Garratts (or perhaps I’m missing the point…).

[LMS2968]

14 hours ago, The Johnster said:

‘0F’ was called ‘unclassified’ on the WR, so therefore equivalent to the LMS Beyer-Garratts (or perhaps I’m missing the point…).

The Garratts weren't exactly poplar with crews, but what they'd have thought at getting a 1361 Class 0-6-0ST in exchange on a 1,500 tons train is probably not repeatable!

[kevinlms]

26 minutes ago, LMS2968 said:

The Garratts weren't exactly poplar with crews, but what they'd have thought at getting a 1361 Class 0-6-0ST in exchange on a 1,500 tons train is probably not repeatable!

An LMS Garratt shunting at the docks, would also look rather silly! Not to mention the former curves now straightened somewhat.