A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 103


Hello Chums

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

'Multiple Jets - Kylchap'

"Undo four nuts and make a bigger hole in the top of the smokebox and you are there."

Arthur Taylor, Chargehand Fitter, King's Cross MPD 'Top Shed'.

Sir Nigel Gresley died in 1941 and was succeeded by Edward Thompson. We'll leap gazelle-like over the controversies of Mr Thomson's time and simply note that he fitted Kylchap exhausts to his 'Pacific' rebuilds, classes 'A1/1' 'A2/1' and 'A2/2'.

He also fitted his new 'Pacifics', class 'A2/3', with the Kylchap exhaust.

Mr Thomson retired in 1946 and was succeeded by Arthur Peppercorn. It's fair to say that many of the staff of the locomotive department, including in the Drawing Office, had an uneasy relationship with Mr Thompson and found Mr Peppercorn a much more agreeable chief. They were keen to put the Thompson years behind them and remove as many idiosyncratic Thompson features as they could from any further 'Pacifics' to be built.

Which sort of explains the story that went round that the Peppercorn 'A2' 'Pacific' class were fitted with single chimneys as a reaction against Mr Thompson's use of the Kylchap exhaust. Incidentally, 'P2' 2-8-2 No. 2005 Thane of Fife had a single blastpipe and chimney, but when Mr Thompson rebuilt her as an 'A2/2' she was given a Kylchap exhaust like the rest of the class.

There were 15 Peppercorn 'A2' 'Pacifics', entering traffic from December 1947 to August 1948. The last one, No. 60539 Bronzino (splendid name!), was fitted with a Kylchap double blastpipe and chimney. It had been noticed that the locomotives fitted with a single chimney were not quite as good as had been expected. Bronzino was a fine engine and it was arranged to fit five others with the Kylchap exhaust during 1949. Which gives an opportunity to have another list of engines. The five were:

60526 Sugar Palm
60529 Pearl Diver
60532 Blue Peter
60533 Happy Knight
60538 Velocity

Given that the double-chimney 'A2s' were better engines, I wonder why they were not all converted. Maybe someone will be able to enlighten us in the discussion.

Also, the double-chimney engines were dispersed across the E, NE and Sc regions, from Ferryhill (Aberdeen) to King's Cross. One would have thought it would have been good to concentrate them where they could be most effective; the difficult Edinburgh to Aberdeen line being an example.




['A2' 'Pacific' No. 525 AH Peppercorn new at Doncaster Works on 31 December, the last day of the LNER. Mr Peppercorn and some of his staff pose beside the locomotive.]


The lesson regarding the Kylchap exhaust had been well-learnt and all of the Peppercorn 'A1' class, entering traffic between August 1948 and December 1949 were fitted with it from new.

***

But what about the Gresley 'Pacifics'?

By the end of 1948, three out of the four Kylchap-equipped 'A4s' were allocated to 34A King's Cross 'Top Shed'. The fourth, No. 60005 Sir Charles Newton was at Gateshead. At Top Shed, the three Kylchap-equipped 'A4s' were recognised as being superior performers to the single-chimney locomotives. As efforts were made to gradually restore train services to something like pre-War standards, the limitations resulting from the conditions prevailing in the late 'forties and early' fifties became apparent. These were difficult years in Great Britain.

The steaming of the single-chimney 'A4s' was beginning to give cause for concern. The Kylchap-fitted engines would steam freely without the skill and attention of the enginemen required by the single-chimney locomotives. It was becoming difficult to recruit new staff of the calibre required and many of the most experienced enginemen and shed staff had retired or were about to do so.

Monopolies, especially state monopolies, are rarely conducive to customer choice and nationalisation of the coal industry meant that the railways were much less able to specify coal from particular collieries. There was also a massive export drive in progress to try to repair the country's finances, which led to much of the best coal going for a sail on a ship.

A combination of some less experienced enginemen and shed staff, and poorer coal did not agree with the single-chimney 'A4s', or 'A3s' for that matter.

A feature of BR, when under the centralised control of the Railway Executive, was movement of senior officers between regions. Which led to KJ Cook, a GWR then WR man, becoming Chief Mechanical Engineer of the ER and NER in 1951. He brought many good Swindon practices with him, such as optical alignment of the frames and axleboxes.

However, he was resistant to requests to fit the single-chimney 'A4s' with Kylchap exhausts, firmly believing that the Swindon proportions, perfected by Sam Ell and his team, was all that was required. From 1953, something of a tug-of-war commenced. The CME experimented with variations of the Swindon proportions whilst Top Shed illicitly tampered with the blastpipes in an effort to improve matters.

Meanwhile, senior ER locomotive men such as LP Parker, Motive Power Superintendent, Eastern Region,¹  CN Morris, Divisional Maintenance Engineer at King's Cross and PN Townend, Shedmaster at King's Cross, were pressing the CME to simply fit Kylchap exhausts. The pressure seems to have further entrenched Mr Cook's position and he maintained a, for me, impossible to understand opposition to the Kylchap system. There was even a suggestion that the Klychap exhausts might be removed from engines fitted with it!

By 1957, the single-chimney 'A4s' blastpipes had been reduced to 5 1/8 in. diameter. This resulted in a lot more noise and less efficiency. Efficiency can be seen in coal consumption and the 'A4s' were the only engines which worked the 'Non-Stop' 'Capitals Limited' - the 'Elizabethan' from 1953. Having sufficient coal to complete the journey was essential and coal consumption was a critical factor.

Interestingly, the solution came from Sir Winston Churchill's Conservative Government and its Transport Act, 1953. This disbanded the Railway Executive and devolved a lot of responsibility to the Regions, which now reported direct to the British Transport Commission. The Regional General Managers were given significantly more power, including an organisational line to the motive power depots.

King's Cross did a series of tests and calculated the saving in coal per mile of the Kylchap engines was 6-7 lbs which would quickly pay for the conversion to Klychap exhausts.

The CME maintained that the conversion would be expensive. Before the War, Kylchap apparatus had cost £400-£500. The patent had expired in 1941 and it would now cost around £200 for an 'A4' and £153 for an 'A3'. Regarding the difficulties posed by the installation, it had been suggested a new inside cylinder casting would be required. To test if this was true, Mr Townend instructed Arthur Taylor to measure up everything inside the smokeboxes of a Kylchap and single-chimney 'A4' and report what would be required to change a single blastpipe locomotive to a Kylchap.

Mr Taylor's conclusion was priceless and made a splendid introduction to this part.

The CME had been outmanoeuvred and the General Manager was keen to see his cost savings.  No. 60017 Siver Fox emerged from Doncaster in May 1957 with a Kylchap exhaust. She had been a very good engine but had lately developed a reputation of being a shy steamer. She was transformed and was now a superb locomotive. All of the class were converted by November 1958. As far as I can ascertain, the last to be converted was No. 60032 Gannet, which emerged from Doncaster Works on 27 November 1958.

As we saw, the 'Swindon' dimensions used on single-chimney engines by 1957 resulted in a single 5 1/8 in. diameter blastpipe. Lots 'N' lots of noise, high back pressure and, unfortunately, potentially dodgy steaming on post-War coal. The Kylchap exhaust fitted to the 'A4s'had two blastpipe tops of 5 in. diameter - much better. 




[Sir Nigel Gresley, as converted with a Kylchap exhaust in December 1957. The Minitrix model depicts her in preserved condition as, of course, she didn't have a double chimney in LNER days.] 


After authority had been given to convert the 'A4s', Mr Townend and his colleagues conducted coal saving tests on 'A3s'. This was a little less than for 'A4s', at 6 lbs per mile, but still made the Kylchap conversion viable. Commencing with No. 60055 Woolwinder in June 1958, the conversion of the 'A3s' was complete by the end of 1959. The transformation of the 'A3s' was remarkable and was proof, if any were really needed, of the excellence of the Kylchap exhaust.

But the SuperSmelly diesels were coming. This led to an interesting development. The 'V2' 2-6-2s, like all Gresley engines, were good steamers but the fitting of spark arrestors in their smokeboxes under BR had caused steaming and performance to decline. The diesels were entering service and failing. Which meant the Peterborough standing pilot was kept busy. And Peterborough's turntable couldn't take a 'Pacific'; the biggest engine it could manage was a 'V2'.

After a straightforward double chimney was fitted to No. 60817, to no special advantage, common sense took over and six 'V2s' were fitted with Kylchap exhausts. They were exceedingly good engines - a couple were at Peterborough for standing pilot duty and 'Top Shed' made good use of the others, especially on fast freights to York. They saw some passenger work as well and an Inspector riding on No. 60881 had to instruct the driver to close the regulator due to the speed at which the train was travelling. 95 mph!

For details on the conversion of the Gresley locomotives to Kylchap exhausts, I have relied heavily on the writings of the late PN Townend, without whose tenacity I doubt whether it would have been achieved. I have included two valuable sources in the footnotes at ² and ³.

**

So ended steam locomotive development for main line railways in Great Britain. As I mentioned before, the air-gas-steam-exhaust circuit was, I believe, the last piece of unfinished business. We have seen various, and sometimes contradictory, developments in the BR era, right up to 1962. Several locomotive engineers furth of Great Britain continued development, but that is beyond the scope of this mini-series.

Let's return to the Kylchap exhaust. As I mentioned earlier, the 'chap' part of the name came from M. André Chapelon, who developed an earlier system, primarily by adding a third stage nozzle or cowl. We noted the second stage is the Kylälä spreader, which was a vital component of the earlier system. Hence the 'Kyl' part of the name.

The earlier system was the creation of a Finnish engineer, Kyösti Kylälä.

I told you we'd Finnish with a Finn!

FINIS


¹ LP Parker was a remarkable railwayman. The late Mr Hardy has written of him with great respect and affection. He retired in 1955 and died a year later, so didn't see the transformation of the Gresley 'Pacifics' by the fitting of the Kylchap exhaust that he had worked hard to bring about.

² PN Townend, Top Shed, Ian Allan, Shepperton, 1975. Mr Taylor's quote is on page 148.

³ PN Townend, East Coast Pacifics at Work, Ian Allan, Shepperton, 1982.

**

As we've reached the end of this staggeringly brief mini-series, I'd like to conclude with acknowledgements and thanks. I wrote it primarily for entertainment, thank you to those kind people who mentioned they found it informative.

@Bealman , @Nbodger and @port perran kindly provided photographs - thank you.

@martyn , @Hailstone and Ted were of enormous help in commenting on drafts and suggesting improvements. Without their kind and patient assistance, the mini-series would have been much less accurate - my profound thanks to all three.

Any remaining errors, omissions and embarrassments are entirely my responsibility.

@Tank must spend lots 'N' lots of time and money on our FabulousForum which gave me a welcoming place to write about steam locomotives from a modeller's perspective. Thank you.

Thank you to everyone who contributed to the discussion or left encouraging 'reactions'.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-bye

John

Going just slightly  but it is related to P2 2001's trip to France for testing.

By coincidence, my local historical society has published a letter this month concerning the outward trip of the loco. Naturally enough, the loco arrived at Parkeston shed, the nearest one to the ferry (about a mile away, you could see it from the ship) chimney first. However, for whatever reason, the ship required the loco tender first on the ship, which meant turning the loco before loading. However, the Parkeston shed turntable was too small.....

No problem, the Harwich branch had, and still has, north and south facing junctions with the main line.

So the letter tells how the loco was reversed along the branch to Manningtree, about ten miles, turned on the triangle, and then worked tender first back to Parkeston shed and then finally to the ship.

The loco took with it a wagon full of spares, and three 40T bogie coal wagons filled with coal, plus brake van. It worked to Parkeston via the Cambridge main line to north London, and then back down the Colchester line to the Harwich branch, as it was too heavy to go via Bury St Edmunds and Ipswich. A similar route was taken when 10000 was exhibited at Ipswich.

Hope the short trip working has been of use.

Back on topic, as part of the trials in the UK, a number of different arrangements of the Kylchap exhaust were tried out, involving changes to the blastpipe top, taper blocks and cowls before an acceptable solution was found. Chapelon thought that this was rather different from his findings in France, but on testing in France, after once again using  a variety of settings and sizes, the UK solution, with some small adjustments, was found to be probably best overall, and that's how the engine was set when it returned to the UK. Before leaving France it was exhibited in Paris alongside a Nord 'Super Pacific' and a brand new Maybach diesel electric streamlined train.

Martyn

 

Quote from: Bazza on October 30, 2025, 08:47:27 PM

Quote from: Roy L S on October 04, 2025, 06:33:36 PMQuite a significant difference in the roof vent layout

Although presumably not beyond a little modelling effort to correct. And, no doubt, someone can produce appropriate correct 3D printed vents to glue in place.

As I said in post #33 above, a bit of plasticard works wonders, but you are correct, that's not a perfect solution. I appended the mods that could be done on that post also, to do a proper job.

Oh and did I say that the roofs were probably subtly different on each conversion 

It's a minefield. But it can be done to whatever degree you want to. You just need a friend willing to design a replacement roof.

Bob

Quote from: Roy L S on October 04, 2025, 06:33:36 PMQuite a significant difference in the roof vent layout

Although presumably not beyond a little modelling effort to correct. And, no doubt, someone can produce appropriate correct 3D printed vents to glue in place.

Quote from: Roy L S on October 30, 2025, 07:43:41 PM

Quote from: GlenEglise on October 30, 2025, 07:11:28 PMsadly this thread has gone "OFF TOPIC"

It has to an extent true, but the relevance is what was happening in the era the last examples were in mainline traffic which was quite late. Who would have thought that the last Gresley buffets would still be in traffic during the formative years of Punk Rock!

Thank you for saying that so eloquently.
As the Stranglers said in 1977

"I can think of a lot worse places to be [than this forum]
Like down in the streets or down in the sewer
Or even on the end of a skewer"

Bob 

Quote from: GlenEglise on October 30, 2025, 07:11:28 PM

sadly this thread has gone "OFF TOPIC"

It has to an extent true, but the relevance is what was happening in the era the last examples were in mainline traffic which was quite late. Who would have thought that the last Gresley buffets would still be in traffic during the formative years of Punk Rock!

I suppose many a conversation goes "off-piste" at times, and let's face it, if we were collectively having this one as a group face to face in the pub, it would likely deviate from the core topic many times - curly BR sandwich anyone?

Roy

 

sadly this thread has gone "OFF TOPIC"

A reproduction of a poster in the November 1972 Railway Magazine, Vol. 118 No. 859. The original was in colour but the Railway Magazine then only had colour on the front cover. Sometimes there was a separate loose colour picturingham inside.

Still, it was only 20 New Pence. The Bank of England states that's £2.38 in to-day's money.

With all good wishes.

John

What a brilliant series, many congrats John!
I've often tried to understand the Kylchap exhaust system, and never really got to grips with it - now I think I have, thanks to your series.
Looking forward to the next parts.
Cheers! 

Thanks once again, John @Train Waiting , for the short postingham in this brief mini-series.

For those who may want to find out a little more about exhaust design, there are a number of search results in Google, but this link has a short summary of those generally referred to by John, and some more recent ones which won't be covered in this series;

http://www.trainweb.org/tusp/ex_dwgs.html

One problem with fitting smokebox devices was that they often rendered the cleaning of the boiler tubes difficult, as they were 'swept' with a brush on a very long rod, rather like a drain cleaning rod; sometimes, it was necessary to remove part of the exhausts to get to some tubes. The Giesl exhaust was good in this respect, as the thin shape (viewed end on) gave easy access to just about all the boiler tubes. They sometimes also precluded the ability to fit 'self cleaning' smokeboxes, as there wasn't enough space for the cleaning grids. I'll let you do your own research on these, but it was one reason why the V2s had steaming problems, as these grids interrupted the flow of the hot gases through the smokebox and had an effect on the draft on the fire. I'll add a bit more when John has written up about the V2s.

Referring to the P2s, the Aberdeen 'road' was a tough one due to its sinuous nature for such a long wheelbase loco. This meant wear on the crank axle was magnified with the high piston loads, and there were failures of the axles in traffic. These failures prompted Mr. Thompson to rebuild the locos as Pacifics; enthusiasts of the time, and also since, have questioned that, as this was during WW2, why the locos weren't just transferred to the easier, straighter, lines of the ECML between King's Cross and Newcastle. Wartime loads were frequently very heavy, and the extra power would presumably have been much appreciated by the loco crews. (Incidentally, a D16/3 'Claud', the former Royal engine 8787, once took an hour to do the 29 miles between Peterborough and Grantham, up Stoke bank; there was 'plenty of steam, it just wouldn't go faster' The load was 17 bogie coaches, a 'normal' wartime load. Twenty plus was not unknown).

If a P2 failed, or after they were transferred, Shedmasters had the sometimes difficult task of finding two replacement locos (to double head) and a second crew. Pacifics were not permitted to be double headed on the Aberdeen run.

Until the next one, John.

Martyn