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

Quote from: lugworm on October 11, 2025, 12:14:06 PMDays of Future Passed, by the Moodies.
Very early psychadelic music.

To be followed by....

Bad for Good, by Jim Steinman.

 Originally written for Meatloaf, but throat problems put the recording back by quite some time, so Jim decided to do it himself. Well worth a listen.

Bad for good not my type of music I'm afraid @lugworm .
It's the first time I've heard it, or remember hearing it, so thank you for sharing.

Days of Future Passed, by the Moodies.
Very early psychadelic music.

To be followed by....

Bad for Good, by Jim Steinman.

 Originally written for Meatloaf, but throat problems put the recording back by quite some time, so Jim decided to do it himself. Well worth a listen.

Are you modeling a diorama?

Would love to see it.

Quite correct, Mick. Memories of boozy college nights return!

Always a good track for the last dance of the night. If you couldn't get a girl then, you stood no chance

Quote from: Moonglum on October 10, 2025, 07:53:19 PMI have just read about his passing on Facebook, always sad to hear. I have to say I never really got into the Moody Blues, I am afraid they lacked a bit of bite for me but I did like "Nights in White Satin"...

RIP John

Tim

I was a very big fan back in the 70s but, interestingly, I never really took to NIWS plus, of all the bands I saw live back in the day the Moodies somehow escaped me.

I have just read about his passing on Facebook, always sad to hear. I have to say I never really got into the Moody Blues, I am afraid they lacked a bit of bite for me but I did like "Nights in White Satin"...


RIP John

Tim

many thanks.
i was at Waddington in 1970-1971, and actually guarded, with my furry mate, XH558 plus others.
remember the TACEVAL  scrambles, not so much hear them as feel them
nothing can equate a Vulcan 4 x aircraft QRA scramble, nor ever will.

also, somewhere on the bomb bay of XH558, is a placque with the late SWMBO and my names, who could ask for more

my question answered, Vulcan 4 + 3 carrier loaded as a unit, so I assume the Valiant 3 + 2 would be loaded the same.
again, many thanks for the link.
regards
alan