Rails of Sheffield have a bit of a special on O Gauge Dapol BR Terriers for £149 (40% off) for those of you who dabble in the big stuff.

Quote from: martyn on Yesterday at 10:28:01 AMJust one thing-in paragraph 3, shouldn't the locos be able to work at shorter cut off for economy?

Yes indeed.  An especially silly typo - now corrected.  Thank you very much.

With all good wishes.

John

Thanks again, John.

Just one thing-in paragraph 3, shouldn't the locos be able to work at shorter cut off for economy? Typically, the LNER Pacifics seemed to have run at 15-20%. Or is this something to do with higher speeds generally obtainable from these, and other passenger express, locos?

Martyn

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 59


Hello Chums

Some More About Valves - Part II - the Slow Adoption of Long Lap - Long Travel Valves

As mentioned in Part 58, we will now discuss valve travel.

In slide valve days, valve travel, which is the maximum amount the valve can move within the valve chest, was modest - somewhere between three and four inches was typical.

As piston valves began to be widely used, locomotive engineers started to grasp the importance of longer valve travel.  The valve will move a greater distance for any given angular movement of the crank from which it derives its motion.  This, in turn, accelerates the initial movement of the valve in either direction and, in conjunction with increased steam lap, enables the valve events to be better defined and the port opening to live steam increased.  Which allows the locomotive to work at shorter cut-offs, resulting in increased economy.

Trust Mr Churchward to Lead the Way

Much influenced by developments in the USA, Mr Churchward understood the importance of long-travel valves and, as early as 1902, had designed 10 inch diameter piston valves with valve travel of 6 inches.  Steam lap was 1 5/8 inches.  Typical contemporary practice was four inch travel and one inch (or less) steam lap.

These valves were used in locomotives from 1903, including 4-6-0 No. 98 and 2-8-0 No. 97.  These were the prototypes of the 'Saint' and '28xx' classes.  The long travel - long steam lap valve had been introduced successfully to Great Britain.

The valve travel was increased in the 'Saint' class to 6 1/4 inches.  Slowly but surely, the GWR refined the Churchwardian principles.  Mr Hawksworth's 'Modified Hall' class 4-6-0 had almost 7 inch maximum valve travel and a steam lap of 1 3/4 inches. GWR practice eventually reached 7 1/2 inch maximum valve travel with the 'County' class 4-6-0.

Unfortunately, Mr Churchward's views went largely unheeded for getting on for twenty years.

Mr Hughes' Near Miss

George Hughes on the L&Y came close to defining the modern locomotive with four 4-4-0s, built in 1908, with both high-degree superheating and piston valves with six inch travel and 1 1/2 steam lap. The locomotives had a remarkable performance and were diagrammed for duties normally performed by an 'Atlantic'.  Unfortunately, the old worry about valve lubrication caused them to be converted to short-travel valves.  A near miss.

Ashford Laps Up Churchwardian Ideas

Down at Ashford on the SECR, REL Maunsell built up a small technical team with Derby and Swindon influences, and longer steam lap and longer-travel valves were used on the 'N1' 2-6-0 and the 'E1' 4-4-0 rebuilds. Mr Maunsell carried on with these good practices after being appointed Chief Mechanical Engineer of the Southern Railway. As an example, his 'King Arthur' class 4-4-0 had 6 9/16 inch valve travel.

The LMS Dithers Over Its Direction of Travel

Matters on the LMS were not so positive - with even modern-looking locomotives like the 2-8-0s for the Somerset & Dorset Joint Railway having short travel valves - 3 3/4 inch in that particular instance.

The appointment of Mr Hughes as its first Chief Mechanical Engineer led to an important development in the sturdy form of his 'Horwich Mogul'.  Unfortunately, Mr Hughes was glad to retire to his garden before the class entered service and his successor, the thoroughly Midlandised Sir Henry Fowler, tinkered with some parts of the design.  But, fortunately, not the important ones.  The class had been designed at Horwich, where they had been reading a a couple of recently-published books, from the USA, on valves and valve gear.

The cylinder and valve design followed recent American practice with 11 inch diameter piston valves having 6 3/8 inch travel and 1 1/2 inch steam lap.  These are strikingly modern figures for a locomotive designed in 1924.




[A thoroughly competent design - the LMS 'Horwich Mogul'.  This example, featuring original livery and number, is a ProperlyPoole Graham Farish model.]
 

I might write a future post regarding the strange goings-on in Derby Drawing office - design work had moved from Horwich to Derby after Mr Hughes retired - but some new locomotives, principally the '2300' 2-6-4T passenger engines introduced in 1927, had excellent cylinder and valve arrangements, influenced by the 'Horwich' 2-6-0s. And other new designs didn't.

Mr Gresley Learns from the GWR

It is well-known that Mr (later, Sir Nigel) Gresley's 'A1' 4-6-2 design, for the Great Northern Railway and perpetuated enthusiastically by the LNER, was greatly influenced by the Pennsylvania Railroad's 'K4' 4-6-2, detailed drawings of which were published in the journal Engineering in 1916.

With the benefit of hindsight, it seems strange that the 'A1' had 8 in diameter piston valves with 4 9/16 inch travel and a steam lap of 1 1/4 inch.  This valve design was too restrictive to take advantage of the excellent capability of the boiler to produce steam.  But, Bert Spencer, Technical Assistant for Locomotive Design, realised this in 1924 and produced a design for longer lap and travel valves.  Mr Gresley decided not to implement it, although the 'A1' class was proving to have a higher coal consumption than expected.

After the well-known interchange trial between 'A1' and GWR 'Castle' locomotives in 1925, in which the 'Castle' had proved superior, especially in coal consumption, Mr Spencer's improvements to the 'A1' design were put in hand. Valve travel was increased from 4 9/16 inches to 5 3/4 inches with steam lap increased from 1 1/4 inch to 1 5/8 inch.  Lead was 1/8 inch.  Incidentally, the inside cylinder's valve had an additional 1/16 inch lap. This, and the increase in boiler pressure¹mentioned in an earlier part, gave rise to the 'A3' 'Super Pacific'.

The cost of the valve modifications was modest - £150 - £190 per locomotive - and performance was greatly improved.  Coal consumption reduced from about 50 lb of coal per mile to 40 lb. Evidence of one benefit of this is the introduction of non-stop working from King's Cross to Newcastle from the summer of 1927 and to Edinburgh from 1 May 1928.

From 1927, three of the 'Big Four' companies had adopted long travel valves with long steam lap.  The LMS hadn't made up its mind.  Fortunately, the 'Royal Scot' 4-6-0 class of 1927, designed in collaboration with the North British Locomotive Company, paid heed to the valve design of the 2-6-4T with 9 inch piston valves having 6 5/16 inch travel and 1 1/2 inch lap.  Lead was 3/16.




[Evidence of the long travel valves fitted to this LMS Fairburn 2-6-4T can be seen in the extended front cover for the piston valve chests, located directly above the cylinder.  This allows for the movement of the front piston valve head at maximum travel. The rear cover is similarly extended.  Thanks are due, once again, to the lovely people at the Lakeside & Haverthwaite Railway where both of the preserved examples of this class can be found².]


The next part will conclude our discussion of valves and summarise the importance of Mr Churchward's contribution to British locomotive practice. Then we will move on to other things.

¹ From 180 psi to 220 psi.

² The final LMS development of the 2-6-4T locomotive which began with the '2300' class mentioned ante.  Charles Fairburn was appointed Chief Mechanical & Electrical Engineer (CM&EE) of the LMS when Sir William Stanier formally resigned in 1944. He had been seconded full time to the Ministry of Production as Scientific Adviser since 1942. Mr Fairburn was a distinguished electrical engineer and Mr Ivatt the Younger looked after the steam locomotive side of things.

Mr Fairburn died in late 1945 and Mr Ivatt was appointed as CM&EE with effect from 1 February 1946, having undertaken the role in an acting capacity since Mr Fairburn died.

Whilst clearly Ivatt engines, the convention is that the head of the department takes the credit (or blame) for locomotives introduced, even if they had little to do with the design.


'N' Gauge is Such Fun

Many thanks for looking and all best wishes.

Pip-pip

John

Amazing. You have a talent for explaining this stuff, John.

Quote from: Newportnobby on January 23, 2025, 07:51:05 PM

Quote from: port perran on January 23, 2025, 07:19:21 PMI'll reserve judgement until I hear a bit more tomorrow.

Try the first 3 tracks on 'God's great banana skin', Martin (2 of which I posted above)

Yes, very nice but just hovering below the surface for me.
It just all seems just a bit laboured and never rises above the pleasant mediocre.
As I say, perfectly listenable but not absolutely my cup of tea.

I'd consider nick' s solution or look at dapol @Foxhound Rob

I'm pretty sure the Stone faiveley is the one sought as the cross arms were only on a selected few 86s back in the day.

Good luck fitting one if find one

Quote from: crewearpley40 on January 23, 2025, 02:37:00 PMRob [ As I was posting so was nick , probably that's the route to aim for ( dapol )

https://railsofsheffield.com/products/stone-faiveley-pantograph-pair


Stone faiveley prior to c. 1984
https://www.rmweb.co.uk/forums/topic/68282-when-did-class-86-pantographs-change/

http://www.flickr.com/photos/robinidle/4937029450/
86420
https://www.westernthunder.co.uk/threads/25kv-stuff-old-and-new-and-other-electrics.11682/page-2

Thanks lads, much appreciated.

Quote from: Browning 9mm on January 24, 2025, 08:35:29 AMI pray that none of us get leaves or snow, nor floods, on our rails today

I'm very grateful I don't line in North Cornwall, a tornado touched down at Quintrell Downs yesterday and the area around Newquay did suffer some damage. There's trees on the line on the Bodmin & Wenford.

I did have a tree down on the layout this morning, due to my own hamfistedness. Luckily, it wasn't on a running line.

A wonderful description again, John, of a complex operation.

Many thanks.

Martyn