Ex LMS 2P 4-4-0 and Compound 4-4-0

[Roger Sunderland]

Hi there

Can anybody please tell me what the differences in boilers and fireboxes were for the above 2 locos. I’m thinking particularly of the length of the boilers and fireboxes. Many thanks.

[PenrithBeacon]

Boilers were very different. The 2P was the same as the 4F (although I'm pretty certain they weren't interchangable) but the 4P Compound was a lot larger.

The RCTS book on LMS boilers will give chapter and verse  

[LMS2968]

The 2P (and 4F) used the same G7S boiler. The 7 was the firebox length and the S meant superheated. Barrel diameter outside front ring was 4' 8" and length between tubeplates was 10' 10 1/2". The Compounds (and first S&DJR 2-8-0s) used the G9AS boiler, firebox length 8' 0", diameter 4' 8" and 12' 3 5/8" between tubeplates. Neither was regarded as a good steamer.

[Compound2632]

7 hours ago, LMS2968 said:

Neither was regarded as a good steamer.

 

Yet the G7S was fitted to a very large number of locomotives so it can't have been so very poor. The 2Ps were highly-regarded engines where there wasn't prejudice against them, for example, on the G&SW section.

[LMS2968]

The two classes with that boiler were the 4F, which had reasonable steam passages whereby the cylinders could use all the steam the boiler could produce. Generally, they weren't too bad for the first few hours but tended to go down the nick thereafter. The 2Ps' steam circuit was very restricted so the boiler could produce more steam than the cylinders could receive. At low speeds, this wasn't an issue but became so as speed rose. It is brought into focus when the drivers of Stanier Pacifics complained about having 2Ps as pilots on the heavy overnights as far as Rugby. They helped on the climb to Tring but after that, as speed rose, the Pacific was not only pulling the train but pushing the 2P. They'd have been much happier without the 'assistance'.

[Compound2632]

@LMS2968, I'm confused. In your first post you say the boiler was a poor steamer, then in your second you say it produced more steam than the engine could use.

[pH]

11 hours ago, LMS2968 said:

The 2P (and 4F) used the same G7S boiler. The 7 was the firebox length and the S meant superheated. Barrel diameter outside front ring was 4' 8" and length between tubeplates was 10' 10 1/2". The Compounds (and first S&DJR 2-8-0s) used the G9AS boiler, firebox length 8' 0", diameter 4' 8" and 12' 3 5/8" between tubeplates. Neither was regarded as a good steamer.

 

4 hours ago, Compound2632 said:

… The 2Ps were highly-regarded engines where there wasn't prejudice against them, for example, on the G&SW section.

As, according to DL Smith, were Compounds, even after the introduction of 4-6-0s. He specifically describes one occasion where a “run down Compound” was working a train south of Girvan on significantly less coal than a 5 or a Jubilee would have been using.

[LMS2968]

9 hours ago, Compound2632 said:

@LMS2968, I'm confused. In your first post you say the boiler was a poor steamer, then in your second you say it produced more steam than the engine could use.

More steam than a 2P could use, because its valve chests were below the cylinders requiring very tight passages for the live steam and exhaust steam to and from them. This restricted the amount of steam which could reach the cylinders to below what the boiler could generate, so the boiler was never really pushed.

 

The 4F was different. I probably overstated the case here. The 4Fs were reasonable steamers and generally coped well enough; they did a lot of good work over many years, but it has become fashionable to denigrate the. I didn't intend to join the anti-4F Club!

[LMS2968]

To move this on a bit and also to justify my comments, I'd like to look in more detail about the two boilers.

 

G7S: This was a superheated development of the saturated G7 boiler as fitted to the 3Fs and was regarded as a prolific steam raiser. All that was done to make the G7S was to add the superheater: it used the same firebox and grate area so both had the same fire producing the same amount of heat. In the G7, all this heat was used to generate steam, but in the G7S some was diverted to raise the temperature of steam already generated, so less heat was available to produce steam in the first place. The steam raising capacity therefor fell, but the superheating made the 4F a stronger engine than the 3F, justifying the higher power class.

 

G9AS: This boiler's problems go back to the design stage, where an emphasis on free water and steam circulation was a priority. Hot water and steam bubbles rise, and if blocked by an excess of tubes, steam generation is compromised. In this boiler the tubes were widely spaced to allow free circulation, but this reduced the number which could be fitted within the tubeplates, decreasing the tube surface area in contact with the water and so the ability to generate steam. This was less of a problem with the Compounds which, as designed, ran with full regulator opening and short cut-offs, but in any case used the steam twice, once in the high pressure cylinder then again the low pressure cylinders. The S&DJR 7Fs were a different story. Their short-travel gear demanded long cut-offs, especially when climbing that line's steep banks with heavy trains. When five new examples were built in 1925, they were given bigger boilers to aid steaming. Admittedly, when these boilers wore out no new ones were build but the engines converted to the G9AS boiler like their sisters.

 

A lot is revealed in 'Raising Steam on the LMS' by Arthur Cook (1999) RCTS Huntingdon ISBN 0 901115 85 1

[Compound2632]

Thank you, that's very illuminating.

 

2 minutes ago, LMS2968 said:

In the G7, all this heat was used to generate steam, but in the G7S some was diverted to raise the temperature of steam already generated, so less heat was available to produce steam in the first place.

 

As a physicist, I have to quibble a bit here. You are assuming 100% efficiency in transferring the heat to the water in the G7 boiler. That seems to me unlikely - it would mean the gases coming out of the tubes into the smokebox to were back down to ambient temperature. By inserting superheater elements in the tubes, some of that heat that would otherwise go out the chimney is transferred to the steam. Now, because larger tubes were needed to accommodate the superheater elements, the surface area for heating the water is reduced a bit, which would reduce the heat transfer to the water but I presume this was more than compensated for by the heat transfer to the steam. The test would be to measure the temperature of the smokebox gases for G7 and G7S boilers either being fired at identical rates, or producing the same amount of work at the (identical) cylinders. (I'm not sure which, perhaps both.) I shouldn't think such an experiment was ever done; I doubt a 3F or 4F ever darkened the doors of the Rugby test plant!

[Aire Head]

2 hours ago, LMS2968 said:

The 4Fs were reasonable steamers and generally coped well enough; they did a lot of good work over many years, but it has become fashionable to denigrate the. I didn't intend to join the anti-4F Club!

 

Someone should write a bloody book called "in defence of the 4F" 😂

[LMS2968]

I certainly agree with the last bit!

 

The gas temperature at the smokebox could vary a lot depending on the A/S ratio (cross-sectional Area  of the tubes / Surface area of tubes in contact with the water), easily worked out for the small tubes but less so with the flues as the A/S of the elements has to be calculated and subtracted from that of the flues. It was rare and undesirable to get ambient temperature at the smokebox; it was usually high as witnessed by the burnt and crinkled paint. Realistically, you didn't want it lower than the water temperature as this would mean the last few feet of tubes would be extracting heat from the water and therefore reducing the steaming. But the gas exiting the flues was sometime less than the superheated steam temperature, the Stanier Pacifics were a case in point. Attempts to lag these last few feet came undone when the tubes needed rodding out.

[Flying Pig]

1 hour ago, Aire Head said:

 

Someone should write a bloody book called "in defence of the 4F" 😂

 

That would never happen and its conclusions would not be summarised here 

 

https://www.steamindex.com/library/stack/tester.htm

[Compound2632]

2 minutes ago, Flying Pig said:

 

That would never happen and its conclusions would not be summarised here 

 

https://www.steamindex.com/library/stack/tester.htm

 

And the author is on RMWeb from time to time.

[Wickham Green too]

1 hour ago, LMS2968 said:

... the last few feet of tubes would be extracting heat from the water ...

Only possible if the ambient temperature smokebox air was going INTO the tubes .............. which it certainly shouldn't be !

[Compound2632]

3 minutes ago, Wickham Green too said:

Only possible if the ambient temperature smokebox air was going INTO the tubes .............. which it certainly shouldn't be !

 Put the blower on!

[LMS2968]

No, the gases had given up their heat to the elements en-route from the firebox end and were then below the temperature of the elements further back, but at or above the temperature of the water in the boiler.

 

I believe this was substantiated on the Rugby Test Plant.

[Wickham Green too]

So the gases are 'at or above the temperature of the water in the boiler' yet 'lower than the water temperature' at the same time ......................... hmm - doesn't tally with wot they taut me in fizziks A Level !

[Flying Pig]

15 minutes ago, LMS2968 said:

No, the gases had given up their heat to the elements en-route from the firebox end and were then below the temperature of the elements further back, but at or above the temperature of the water in the boiler.

 

I believe this was substantiated on the Rugby Test Plant.

 

 

Superheaters are a bit weird as heat exchangers go, as the steam being heated flows counter to the exhaust gas on the way out and then returns in the same direction as the gas.  It could well be that maintaining steam temperature below that of the exhaust throughout is only possible with less than optimum heat transfer overall.  It would need careful analysis to elicit the ideal temperature gradients.

 

[LMS2968]

. . . as per G.J. Churchward's theories about low degree superheat.

[Compound2632]

But were all G7 boilers, or all G7S boilers, the same in the number, diameter, and layout of tubes? they were built in large numbers over a long period and, as types, were in service for over half a century. 

Edited March 18, 2023 by Compound2632

[LMS2968]

Not in tubes, no. They were the same boiler and firebox shell but with different tubeplates. Some of the G7's small tubes were sacrificed to make room for the flues of the G7S. The G7S had 21 flues 5 1/8" diameter and 146 small tubes 1 3/4" diameter, the elements being 1 1/2". Unfortunately, Mr Cook does not give the information for the G7 but there would have been more small tubes with no flues.

[Compound2632]

2 minutes ago, LMS2968 said:

Not in tubes, no. They were the same boiler and firebox shell but with different tubeplates. Some of the G7's small tubes were sacrificed to make room for the flues of the G7S. The G7S had 21 flues 5 1/8" diameter and 146 small tubes 1 3/4" diameter, the elements being 1 1/2". Unfortunately, Mr Cook does not give the information for the G7 but there would have been more small tubes with no flues.

 

I intended two distinct questions:

• did all G7 boilers have the same tube layout?
• did all G7S boilers have the same tube layout?

In other words, does the data you give apply to all, or only some?

[LMS2968]

Ah, sorry. My mistake. As far as I know - and I don't claim any expertise - they were all the same. They're the figures Arthur Cook gives for the G7S and I've never read of any changes in the layouts. I doubt there would be many changes to the G7 as it was already a successful type. But the art of correct ratios wasn't known, even into the mid-1930s (witness the Stanier 5XP debacle) so there might have been some experimentation. The G7 was fitted to several different classes over a long period so who knows what went on previously.

[Roger Sunderland]

Wow. Pardon me for starting this discussion. I only wanted to know if there was a difference in length of the boilers!