Thanks again, John.

I'll add  a few comments after your next post, as I think they will be more appropriate then.

Martyn

Quote from: Bealman on October 11, 2025, 11:58:34 PMTo answer your question about the Peco Jubilee, it is my belief, yes.

Fantastic series, John.  

It's amazing how good it still looks, despite the complete absence of the parts of the motion that control the valve travel lead - i.e the drop link, union link and combination lever.

To answer your question about the Peco Jubilee, it is my belief, yes.

Fantastic series, John.  

Quote from: Trainfish on October 11, 2025, 09:26:42 PMI don't have a glass which says cider house.

Maybe Rosie has one

I don't have a glass which says cider house.

Quote from: Trainfish on October 11, 2025, 09:03:42 PMErm, that's cider in that glass 

Your fault. You put it in a glass stating 'Ale House'

Erm, that's cider in that glass 

At last! An ale you can see there's no pondlife in

Who says I have all the Peco Ford vans? Oh, Mick @Newportnobby did. Well he was wrong as these arrived this week to bring the total up to 45 



As did this:

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 94


Hello Chums

The Final, Exhausting Section of Our Gloriously Brief Mini-Series

'Blastpipes - Some Theory-Type Stuff, but with Stories'

The conical blastpipe, pioneered by Timothy Hackworth and taken up by Robert Stephenson was essential to provide sufficient draught to enable a multi-tube boiler to steam well. As the engine worked harder, the exhaust sharpened and increased the draught. Magic!

But, there's a but. Why is there so often a but? Restricting the surface area of the blastpipe will help steaming, at the risk of pulling the fire to bits - we'll have a Saintly little story about this in, probably, the next part - but it causes increased back pressure in the cylinders. Put simply, the constricted blast pipe means exhaust steam will be tempted to linger longer in the cylinders rather than making a sharp exit through the valves and away out to the sky. Increased back pressure causes increased coal consumption. Which meant locomotive engineers had to think carefully about how much to constrict the blastpipe.

Robert Stephenson recognised this and mentioned it in correspondence. His point was sadly misrepresented in the BackTrack article mentioned in Part 93. Let's turn to the invaluable Dr Tuplin for a succinct explanation:

'The ideal was the largest [blastpipe] nozzle that would enable the engine to steam at full power in conditions somewhat inferior to normal ones. If average conditions deteriorated over the years, what was originally satisfactory might cease to be so and should be changed.'¹

Very nicely put, Dr T.

However, in practice, things could be a bit more complicated and the enginemen might end up with a locomotive that was steaming badly. Their traditional answer was to restrict the blastpipe nozzle by means of a home-made (or shed blacksmith-made) device. These had several names - 'Jimmy' and 'razor' being familiar to me. Please feel free to add any other in the discussion. This improved the engine's steaming but it was important not to get caught using one. Authority would not be happy.

But here's a nice little story. When Mr Stanier, later, Sir William, introduced his '5XP' three-cylinder 4-6-0s on the LMS in 1935, they were poor steamers. Possibly even terrible steamers. As a Great Western man, Mr Stanier had no experience of three-cylinder engines. Amongst a series of modifications, guess what they did. Yes, reduced the area of the blastpipe's nozzle. Of course, they used a nice new cap rather than a home-made 'razor' but the effect was the same.




[An LMS '5XP' or 'Jubilee' 4-6-0, made by Rivarossi for Peco. Is this the most influential British 'N' gauge locomotive of all time?]


Then, nearly 20 years later, BR had a steaming problem with its brand new 'Standard' '5MT' 4-6-0s. Whoops! The LMS 'Black Fives, on which the BR design was based, on tended to be good steamers as, of course, were the GWR 'Halls'. Whatever could they do? Yes, they reduced the blastpipe cap from 5 1/8in. to 4 7/8in. Evaporation of water increased from 19,000 lb./hr to 24,000 lb./hr. ES Cox, who had responsibility for the design of the BR 'Standards', helpfully included details of this in an interesting book.² Mr Cox's description is worth reading if you have an interest in such things. He discusses smokebox vacuum and blastpipe pressures which are, I think, beyond the scope of our Coarse Guide. Important stuff, though, and please feel free to mention them in the discussion if you wish.




[A BR 'Standard '5MT', No. 73072, with high-sided tender of 9 tons coal and 4725 gallons water capacity.  Built at Derby for the LMR as part of the 1953 Building Programme. Entered service on 11 December 1954, allocated to Chester. Transferred to Polmadie on 22 November 1958 and withdrawn from there on 27 October 1966. Not even a dozen years' service - what a waste!  My late Father-in Law was an engineman at inverness and thought highly of these locomotives. He preferred them to 'Black Fives'. Photograph from my non-collection. I think it's an official BR one.]


But, there we were, in the era of the BR 'Standard' locomotives and we were still working out important design features by trial and error. In the BR example, a 26% increase in evaporation rate (a good metric for 'steaming') was achieved by reducing the blastpipe diameter by 1/4 in. after the class had entered service. By the way, before they went down to 4 7/8 in., they tried 5 in. which gave a water evaporation of 22,000 lb./hr.

This rather supports my contention, made earlier, that this exhausting matter was the last major area of unfinished business at the end of steam locomotive development in Great Britain. A policy decision, made at the start, was that the new BR 'Standards' would have conventional single blastpipes and chimneys. So, why did some locomotives of Class 9 and 4 have double chimneys?³ More of this later.

One last point, a very sharp blast could cause damage to railway infrastructure such as footbridges (Poppingham's now has smoke plates - thank you @icairns) and station canopies.

¹ WA Tuplin, British Steam Since 1900, David & Charles, Newton Abbot, 1969, Page 44

² ES Cox, British Railways Standard Steam Locomotives, Ian Allan. London, 1966, Page 132.

³ As did the '8P' 4-6-2 No 71000, Duke of Gloucester. This engine was not in the original plans for the range of 'Standards'.

Special thanks, once again, to @martyn for reviewing the draft and making helpful comments thereon.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Tickety-tonk.

John