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Steam Loco Power ratings


david130653
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Apologies for my ignorance but I wondered if someone can explain fully how the power ratings for a steam locomotive were worked out? By this I mean several things:

 

  1. What was the difference between the F (freight) Rating and P (passenger) Rating?
  2. What did the number, e.g. 0P or 9F actually mean, in terms of power?
  3. Some Mixed Traffic Locos were given an equal Passenger and Freight rating, e.g. 5MT, whereas others were rated 5P4F. Why?
  4. The 9F B.R. Standard freight loco was often used to haul passnger trains, what would its P rating have been?

 

Thanks in advance.

 

David

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Apologies for my ignorance but I wondered if someone can explain fully how the power ratings for a steam locomotive were worked out? By this I mean several things:

 

  1. What was the difference between the F (freight) Rating and P (passenger) Rating?
  2. What did the number, e.g. 0P or 9F actually mean, in terms of power?
  3. Some Mixed Traffic Locos were given an equal Passenger and Freight rating, e.g. 5MT, whereas others were rated 5P4F. Why?
  4. The 9F B.R. Standard freight loco was often used to haul passnger trains, what would its P rating have been?

 

Thanks in advance.

 

David

 

The system started on the MR about 1906. The LMS modified it based on some data derived by the L&YR and finally BR modified it again to give the final version so there are subtle differences in meaning depending on the era. The systems essentially tried to work out drawbar pull at either 25mph or 50mph

 

The LMS system was based on the mean effective pressure curve produced by the L&Y. It took the LOWER of two values:

 

a. The cylinder tractive effort based on the MEP curve at 50mph for passenger (P) or 25mph for freight (F) locos.

b. The boiler power based on 130lb of coal per sq foot of grate area per hour giving 6.15lb steam per pound of coal and steam rates of 25lb or 20lb per indicated horsepower for superheated and saturated locos respectively.

 

Initially the scale ran from 1P - 5P and 1F - 6F with each power class covering a bracket of performance.

 

Thus

 

Class TE at 50mph in tons Class TE at 25mph in tons

 

1p 1.5 - 2 1f 2.85 - 3.6

2p 2 - 2.5 2f 3.6 - 4.35

3p 2.5 - 3 3f 4.35 - 5.1

4p 3 - 3.5 4f 5.1 - 5.85

5p 3.5 - 4 5f 5.85 - 6.6

6f 6.6 - 7.35

 

 

They later extended to the higher powers based on the known performance of the new engines.

 

BR used a different set of formulae to get pretty much the same results but eliminated some of the anomalies. They used a factor which came out of a formula involving free gas area, grate area and starting TE and another diffreent set of tables.

 

This is described very fully in P Ransome Wallis's book "The last steam locomotives of Bristish Railways" pages 183-185. For freight locos like the 9F the BR classification was based on the LOWER of the nominal tractive effort or the adhesion weight divided by 4.5. (The two numbers are 39677 and 38577 for a 9F putting it well above the top end of the 8F range which was 34000).

 

If you use the passenger formula to get the passenger classification for a "9F" it comes out as a factor 878 which would put it in the 7P group (i.e. between 601 and 900). That's assuming that I've crunched the numbers correctly.

 

Andy May

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Thanks Andy. That will take me a while to think about, but I really appreciate the comprehensive reply.

 

I am surprised at the way the 9F comes out in terms of Passenger power, I would have expected it to be a lot higher, the first "9P". The most powerful British passenger locos were 8Ps - A4s, Princess Coronations, etc. Though in the case of the latter, and I may be getting very mixed up here, I understand that the maximum power output was never successfully measured as without a mechanical stoker, it was not possible to shovel coal into the firebox fast enough to keep up with the rate it was being used. So would I be correct in thinking the P & F ratings are just theoretical and could be exceeded or not reached in reality?

 

I would have expected the 9F to exceed an 8P - though please do not think I am disputing your maths! I am just basing this on a few very non-scientific observations:


  1.  
     
  2. The Stanier Black 5 was rated 5MT or 5P5F, the 9F would outhaul the Black 5 on freight, according to the maths the 9F comes out at 7P9F, which seems a bit strange to my ignorant ears.
  3. The 9F would also outhaul an A4 or Princess Coronation when, in their later years, they were put onto freight workings (travesty!), so would their frieght rating be much lower than their passenger rating? e.g. 8P 6F?
  4. The "Britania" Class were rated 7P, with the same boiler, so rating the 9F at 7P just seems low.
     

Now I really do accept I have not got a scientific leg to stand on with my purely observational reasoning, so I am probably talking complete rubbish - please feel free to tell me so!

 

 

Regards,

 

David

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  1. The 9F would also outhaul an A4 or Princess Coronation when, in their later years, they were put onto freight workings (travesty!), so would their frieght rating be much lower than their passenger rating? e.g. 8P 6F?

 

Regards,

 

David

 

David,? 

 

 

On what do you base that observation? ? A 9F is considerably smaller, particularly the boiler, than a Princess Coronation, an A1 or a Merchant Navy. ? As the boiler is the main determinant of steam locomotive performance any of these Pacifics would leave a 9F gasping in their wake. ? The only 'advantage' a 9F might be considered to have is that it's smaller driving wheel diameter give it, in essence, a 'lower gearing' so enabling a smaller boilered locomotive to get a heavy freight train underway. ? As driving wheel diameter is a divisor in the tractive effort calculation a smaller wheel diameter gives a higher tractive effort all other things being equal.

 

In U.K. conditions no locomotives were ever expected, or able on our congested networks, to work flat out mile after mile as they did, say, in the U.S. Consequently the Princess Coronations never needed a mechanical stoker to meet U.K. operating conditions. ? Locomotives of their size would have needed them in the U.S.

 

Arthur

 

 

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? A 9F on passenger work designed for a Duchess would simply not work out in practice. The Duchess was designed to haul lengthy passenger trains with sustained power output at high speed over long distances.? 

 

To put things in a latter day perspective, a Class 31 could easily haul a 13-coach train with a 'dead' steam loco tagged on the end the 3 miles from Llandudno to Llandudno Junction, but a Class 31 was found unable to keep time on 5 coaches working a regular interval service between Manchester to Bangor.

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Well I never said I was right or scientific in my observations!

 

My questions around the 9F are based on its ability to run at sustained high speeds - 90MPH plus hauling passenger trains, which appears to put it into express passenger capabilities.

 

As for a mechanical stoker on a Duchess, it was a damn close thing. It was reckoned that the maximum size firebox that could be manually fired was 50sq. feet and the Duchess firebox was 50 sq. feet. Mechanical stoking was considered, but along with a decent sized tender, the LMS management chickened out. So the LMS London-Glasgow service was slowed down from a potential sub 6 hours to a less demanding 6 1/2 hours and staged a stop at Carlisle instead. On the LMS drawing board was a larger loco, a 4-6-4, this time mechanically fired, that would have been built, but the war intervened. So there was demand for higher power and a non-stop Anglo-Scottish service. Wonder what it's power rating would have been?

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I am wonderfully ignorant about what makes a steam locomotive go, so have no scientific input here. That said, express passenger locos have always had large driving wheels, while the 9F had, I think drivers of only 5 ft diameter. Even I can appreciate that that meant the 9F's wheels, and hence all the rest of the reciprocating mechanism, were revolving at much higher RPM for a given track speed than a purpose-designed passenger loco. The fact that they were good at it may say more about how well they were designed and built, in precision engineering terms, than about their suitability.

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Well I never said I was right or scientific in my observations!

 

My questions around the 9F are based on its ability to run at sustained high speeds - 90MPH plus hauling passenger trains, which appears to put it into express passenger capabilities.

 

As for a mechanical stoker on a Duchess, it was a damn close thing. It was reckoned that the maximum size firebox that could be manually fired was 50sq. feet and the Duchess firebox was 50 sq. feet. Mechanical stoking was considered, but along with a decent sized tender, the LMS management chickened out. So the LMS London-Glasgow service was slowed down from a potential sub 6 hours to a less demanding 6 1/2 hours and staged a stop at Carlisle instead. On the LMS drawing board was a larger loco,? ? a 4-6-4, this time mechanically fired, that would have been built, but the war intervened. So there was demand for higher power and a non-stop Anglo-Scottish service. Wonder what it's power rating would have been?

David,

 

That 9F ability to run at 90 mph with a passenger train is just the type of operation where, over several miles, a big pacific would start to show it a clean pair of heels and it's steam raising capacity would tell.

 

Yes, elsewhere, as I said, a 50 square foot firebox would have demanded a mechanical stoker but under U.K. operating conditions it was possible for a fireman to cope, there was not a continuous demand for maximum steam output.

Again, you're quite correct the proposed Stanier 4-6-4's and 4-8-4's would have been so fitted but it's a moot point whether such powerful locomotives could have been utilised to their maximum capacity under the railway conditions of the 1940's and 1950's. ? The drawing office may have considered them, whether the operating department wanted them is another thing.?  Gresleys P1 2-8-2's never fulfilled their potential because of the the railway conditions prevailing at the time (lots of slow freights, short passing loops, conflicting traffic movements).

Pity, they'd have been awesome.

 

Arthur

 

Also, fitting mechanical stokers demanded the provision of special coal and coaling facilities, at some cost. ? When B.R. fitted three 9Fs with them the firemen had terrible problems as they were soon being coaled with whatever was available. ? I think it was in one of Terry Essery's books where he describes a trip over the S&C. ? He spent a lot of the trip in the bunker breaking up the giant lumps of coal that were jamming the screw feed. Harder work than firing he reckoned!!

 

 

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Well I never said I was right or scientific in my observations!

 

My questions around the 9F are based on its ability to run at sustained high speeds - 90MPH plus hauling passenger trains, which appears to put it into express passenger capabilities.

 

As for a mechanical stoker on a Duchess, it was a damn close thing. It was reckoned that the maximum size firebox that could be manually fired was 50sq. feet and the Duchess firebox was 50 sq. feet. Mechanical stoking was considered, but along with a decent sized tender, the LMS management chickened out. So the LMS London-Glasgow service was slowed down from a potential sub 6 hours to a less demanding 6 1/2 hours and staged a stop at Carlisle instead. On the LMS drawing board was a larger loco, a 4-6-4, this time mechanically fired, that would have been built, but the war intervened. So there was demand for higher power and a non-stop Anglo-Scottish service. Wonder what it's power rating would have been?

 

 

And you also have to look at further practicalities as the capacity of the ashpan could be an influencing factor as well on the mileage possible without taking the loco off for servicing. In fact one advantage of a larger trailing truck, as in a 4-6-4 or 4-8-4, was the space it would create for not just a larger firebox but also a larger ashpan - the ash had to go somewhere!

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First, I Just want to say thanks for all the well-informed replies and conversation.

 

Much appreciated.

 

Instead of a mechanical stoker, should we have looked at oil-firing more seriously? It would certainly have solved the ash problem and much of the other detritus from a coal-burning engine. Though it would not have been a suitable alternative for coal during WW2 as it would have had be imported. Certainly a mechanical stoker would have worked in the mid to late 1950's when BR were persuaded by the Coal Board to take a very poor, powdery coal. Probably too late then to justify the cost of conversion, especially as diesels were on the way.

 

I understand the point Arthur raises about the LNER P1, yes, it could haul trains longer than a single signalling block. But, the LNER then went and bought Garrets to haul the Toton coal trains. Why they never used the P1s is something I have never been able to ascertain. In a similar vein, in the war years when passenger trains were 20+ coaches, the hauling power of the existing locos was challenged and though there are tales of extra-ordinary feats of performance, greater haulage power would have made life much easier. Indeed, I have never found an explanation why the Gresley P2s (one loco I would like to see being brought back from the dead) were not brought down to haul the long Kings Cross trains, prior to them being immolated by Thompson.

 

Back to the original question, did/does a table exist for measuring steam loco output against diesels and electrics? I have read that the original LMS 10000 and 10001 were individually felt to be equal to a 5P, and that the two were to be coupled together to give the equivalent of 8P. It also took a 3,000+ h.p. Deltic to equal an A4. Was there any science behind this, or just test runs?

 

Regards,

 

David

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Hi David,

 

It was the LMS who introduced Garretts on the Toton-London coal trains where they essentially replaced pairs of 4F 0-6-0's so the P1s were not an option. The sole LNER Garrett was for use banking up Worsborough bank.

 

There was a short lived oil burning programme after the war but the problem with oil was that it was imported. Post war this country was bankrupt and we had a massive export drive, imports were to be avoided at all costs, domestic coal was king.

 

Arthur

 

 

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Hi Arthur,

 

Yes, sorry, I got my Garretts mixed up, the Toton-Brent ones were the ones the Midland / Derby designers tried to tell Garrett how to design and instead ruined an excellent locomotive.

 

The coal / oil issue was a political football kicked around just after Nationalisation. I am just reading E.S. Cox's "Locomotive Panorama" at the moment and he tells of how they were told to go oil, then coal, then oil. I have read several accounts of footplate crews in the 50's describing the powder they were made to use as BR got it at a discount from the NCB, top quality coal being exported! It would have really suited mechanical stokers, though I suppose it would have gone straight through the boiler and out the chimney, as it did when manually fired!

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I am surprised at the way the 9F comes out in terms of Passenger power, I would have expected it to be a lot higher, the first "9P". The most powerful British passenger locos were 8Ps - A4s, Princess Coronations, etc.

 

The passenger classification is essentially a measure of boiler power. You would expect a loco with a 50 sq ft grate (Duchess, A1) to be better than a 9F on this basis but a Britannia - 42 sqft grate or A3 - 41.25sqft grate (both 7P6F) to be similar in terms of boiler power. Again if you crunch the numbers for the larger pacifics they would come out above where you might expect the top end of "8P" to be but the real limit there was the fireman so there were no locos classified 9P or 10P. The 9F's could and did time East coast expresses and also the WR "Red Dragon" without too much bother. The smaller wheels meant more wear and tear on the cylinders though which was not such a good idea. All things being equal a small wheeled steam loco will out accelerate a larger wheeled one but will only sustain high speed at the expense of maintenance costs. At very high speeds the problem of getting steam in and out the of the cylinders quickly enough tends to limit the smaller wheeled engine (but that speed was above 90mph for a 9F which had excellent valve design). For most steam era expresses a 90MPH top speed was more than enough.

 

[*]The Stanier Black 5 was rated 5MT or 5P5F, the 9F would outhaul the Black 5 on freight, according to the maths the 9F comes out at 7P9F, which seems a bit strange to my ignorant ears.

[*]The 9F would also outhaul an A4 or Princess Coronation when, in their later years, they were put onto freight workings (travesty!), so would their frieght rating be much lower than their passenger rating? e.g. 8P 6F?

[*]The "Britania" Class were rated 7P, with the same boiler, so rating the 9F at 7P just seems low.

 

A 9F would outhaul a 5MT on both passenger and freight but the larger wheels of the class 5 would reduce maintenance costs on passenger services where speeds were high. On something slow like the "Pines Express" the 9Fs won hands down.

 

Typically the larger passenger engines had a lower F rating e.g an A4 was 8P7F because their lower adhesion weight compared to a 9F limited their brute pulling power at low speed (25MPH). Once up to a decent speed the extra boiler power of the 8P engines would start to tell. The Britannia only got a 6F rating because of the limited adhesion weight compared to a 9F. The boilers were similar but not the same. The Britannia had a larger grate and a larger boiler diameter at the firebox end.

 

Andy May

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Just to add my bit in to the conversation there is a good video

about Evening star and the 9F's.

 

Also if you where on a gradient from a stand and 9F or anything with smaller driving wheels will accelerate quicker than something with larger ones (Bulleid's,Brits,Coronations,A1,s etc) Peter Smith has a good book about the Somerset and Dorset and firing and driving on it called Mendips engineman he also explains about how the diffrent locomotives performed over the line and their steaming qualities.

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Wear and tear on the mechanical parts has been mentioned. Coal, water and lub oil have to be considered also, not to mention ash in the ashpan and smokebox. These considerations stack up against small wheeled locos on long high-speed turns. The 1-in-50 up hill & down dale S&DJR suited the 9F's because speed was not a first consideration. This is why the S&D 7F's lasted so long despite having the same inadequate main brearings as the younger 7F 0-8-0's. The 2-8-0 suited the job in hand on the S&D. The 0-8-0 was intended to be an all-line LMS machine and failed the acid test.

 

LG

 

 

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