A Coarse Guide to the Steam Locomotive for ‘N’ Gauge Modellers

[martyn]

After a little more research, hopefully the tail load for the Gresley long travel valves.

Long travel valves had in fact been fitted to the K3 (the first 3-cylinder GNR Moguls) class, designed in 1917, ie before the A1s. At 'normal' speed for a mixed traffic class, this was not a problem, but extended use on passenger trains meant that at higher speeds, due to various factors, the middle cylinder valve gear overtravelled, causing some internal damage and resulted in the middle cylinder doing more than its fair share of work. This was mitigated by reducing maximum cut off to 65% from 75%. Without getting technical, this was only a partial solution.

However, it did mean that when the A1s were designed, it was a deliberate policy to reduce the valve travel to avoid this problem, and hence they entered service with the short travel valves. The trials proved that the service running of the long travel valves were worth doing, as previously recorded.

Ultimately, the K3s had their valve gear altered to give longer lap, and this was successful, resulting in economies of coal and water, and making them freer running.

Hope this is of interest.

Martyn



 

[fisherman]

I'm another one really  enjoying this series and  learning a lot !

TY

[crewearpley40]

I'm another one really  enjoying this series and  learning a lot !

TY

and I'm enjoying the series too with martyn 's ( and others) input. Long may it continue!

[Southerngooner]

I've spent a week or so reading this series of posts from start to finish and only have one word for them - Spiffing!

Keep up the good work

Dave

[Train Waiting]

I've spent a week or so reading this series of posts from start to finish and only have one word for them - Spiffing!

Keep up the good work

Dave

Thank you very much, Dave.

The best bits of the ultra-brief mini-series have been written by others, who have so kindly contributed to the discussion.

I'm a tad indisposed at present, having been in hospital.  Not, I assure you, a wizard wheeze to avoid the Joy of writing about valve gears.

I hope to resume writing in a few days' time.

Thanks again for your kind remarks and all good wishes.

John

[martyn]

At least you haven't list your sense of humour, John! I take it there will be a straight link on your next posts.

Punning yet again....

Get well soon.

Martyn

[Train Waiting]

At least you haven't list your sense of humour, John! I take it there will be a straight link on your next posts.
[...]

Allan in good time! But you most certainly have the gift of the gab, Martyn.

Thank you for your good wishes.

All the very best

John

[Foxhound]

At least you haven't list your sense of humour, John! I take it there will be a straight link on your next posts.
[...]

Allan in good time! But you most certainly have the gift of the gab, Martyn.

Thank you for your good wishes.

All the very best

John

Wishing you a speedy recovery, John, and a swift return to an excellent series of posts!

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 61


Hello Chums

About a Crank

One of the delights about writing this ever-so-brief mini-series in an episodic format is setting out to write about some part or other of a steam locomotive and then realising something else needs to be discussed first.  A SuperSensible author would draft the complete series first and everything would be totally tickety-boo.  As you have no doubt noticed, at no stretch of the imagination or underwear elastic, could I be described as even SemiSensible.  Which means, before our discussion of the various mechanical contraptions that can be used to operate the valves on our locomotive, we'd better turn our attention to cranks.

*

You might recall the earliest steam locomotives had two outside cylinders and then, in 1830, following advice from Richard Trevithick, Robert Stephenson built his 2-2-0 Planet, with two inside cylinders.  Thereafter, inside cylinders became the norm in British locomotive practice for many years.  Some engineers continued to use outside cylinders but, as we have seen, these became less and less common until Mr Ivatt the Elder reintroduced them on his 'Atlantic' 4-4-2 engines of 1898 for the Great Northern Railway.

A useful feature of engines with two outside cylinders, whether of Mr Stephenson's Northumbrian 0-2-2 of 1830 or Mr Riddles' Evening Star 2-10-0 of 1960, is the connecting rods transmit the force of the piston to cranks on the outside face of the driving wheels. The length of the crank between the axle and crankpin centres is half the piston stroke.  That's why 'Churchwardian' two-cylinder locomotives with 30" piston stroke appear to have such big cranks. 

These cranks are part of the wheel casting, with the crankpins (on which the connecting rods exert force through the 'big end' bearing) shrunk in place and, being outside of the wheels, are get-at-able for maintenance.  They are also reasonably easy to manufacture and permit the use of a plain axle.  The first picturingham shows a trio of plain axles, in this instance from a Union Mills locomotive's wheel set. 1:1 scale plain axles are remarkably similar.  But heavier... much heavier.





Back to Planet.  Robert Stephenson decided to use inside cylinders which meant the cranks could not be on the outside of the wheels.  They had to be between the engine's frames and the only place that could be was on the axle.  Toodle-pip to the simple, plain axle and 'How do you do' to the 'crank axle'.

However, Robert Stephenson wasn't alone in thinking about the use of a crank axle. Also in 1830, appeared Edward Bury's 0-4-0 Liverpool for the Liverpool & Manchester Railway and Timothy Hackworth's 0-4-0 Globe for the Stockton & Darlington Railway, both of which used crank axles.

I cannot say for certain because I wasn't in Northern England in 1830, but it appears Messrs Bury and Hackworth, if not exactly disgruntled with Robert Stephenson, were far from being gruntled.  It appears they thought he had pinched their idea for a crank axle. There followed a bit of a fraught discussion with the claims of Messrs Bury, Hackworth and Stephenson, as the originator of the crank axle, being made by their 'friends'.

Mr Stephenson, whom I regard highly as an engineer and a person, dealt with this in a brilliantly clever way. He pointed out that neither could claim credit for the crank axle as it was used in Braithwaite & Ericsson's Novelty, entered for the Rainhill Trials in 1829.*

As a brief aside, there emerged three 'schools' of locomotive design - Bury, Hackworth and Stephenson. The Hackworth school petered out first, but Bury locomotives were built for many years - Coppernob of the Furness Railway being the best-known. But, in the end, the Stephenson school was triumphant. In my view, it was better and capable of enlargement. 

Earlier on, in Reply 300, @Hiawatha mentioned Kropfachse, in German, or crank axle in English, and included an interesting picture of a crank axle from a BR 44 locomotive which I have reproduced here.  Thank you, Peter.

© Armin Schwarz, from https://hellertal.startbilder.de/bild/deutschland~bahnhoefe-in-rheinland-pfalz~betzdorfsieg/374667/treibachse-kropfachse-einer-schweren-gueterzug-dampflokomotive-der.html

Please don't bother about the details of the axle, which is from a three-cylinder 2-10-0 and, as such, has a single crank. It also looks like a one-piece forging to me. What matters is we have an appreciation of the fundamental difference between a plain axle and a crank axle.

In the next part, we'll have a quick look at a typical British crank axle for a two-cylinder locomotive (thanks, again, to our chums at the North Yorkshire Moors Railway) and then venture into the mechanical contraptions, various, that operate the valves. These had to be driven from somewhere and you have probably worked out where that 'somewhere' normally was, for many years.   


Thanks, again, to Peter.

* Proceedings of the Institution of Civil Engineers, Vol. 16.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John

[martyn]

It looks as if @Train Waiting will be covering the two cylinder crank axle in his next post, but just to lead a bit; these could be 'left hand leading' or 'right hand leading'.

The GER T26/LNER E4 2-4-0s were designed right hand leading, but due to an error by the forge making the first thirty axles, they went to Stratford as left hand leading, which meant that the valve gear on these thirty locos had to be altered to suit. IFAIK, it didn't affect performance, as twenty-nine went for scrap still retaining them.

Until next time, John!

Martyn

[port perran]

I always look forward to these episodes but I'm staggered that we are now up to 61.

If I were to have guessed  have said about 25.

Keep up the good work John.

[Train Waiting]

It looks as if @Train Waiting will be covering the two cylinder crank axle in his next post, but just to lead a bit; these could be 'left hand leading' or 'right hand leading'. [...]

Thank you, Martyn. 'Right hand leading' was the typical arrangement for British locomotives. I understand the main exception was the LNWR which preferred 'left hand leading'. I wasn't aware of that interesting GER fact - thank you for including it in the discussion.

***

I always look forward to these episodes but I'm staggered that we are now up to 61.

Thank you, Martin.  I'm staggered as well. I thought it would take a handful of parts. Which it probably would have with a more competent author than me, who stuck to the core facts and didn't wander down the branch lines of British locomotive development.

***

Valve gears coming up next, although we'll have a picturingham of an ex-NER locomotive first. Valve gears are interesting and we'll meet Robert Stephenson again (hurrah!)*, Mr Hackworth, a Belgian chappie and a fellow who came up with the wizard wheeze of drilling a hole in that highly-stressed locomotive component; the connecting rod. Why?  All will be revealed in due course. We might even wander over to the Talyllyn Railway and think about one of Dolgoch's peculiarities.

* Anyone reading this might have noticed the especially high regard in which I hold three locomotive engineers - Richard Trevithick, Robert Stephenson and George Jackson Churchward. Just imagine having them as dinner guests.

Please feel free to suggest alternatives as my selection is a personal view.

With all good wishes.

Pip-pip

John

[chrism]

Which it probably would have with a more competent author than me, who stuck to the core facts and didn't wander down the branch lines of British locomotive development.

But which wouldn't have made such entertaining reading - as far as I'm concerned you can carry on meandering as much as you like 

[Jim Easterbrook]

"It takes a crank to start a revolution"
(Cambridge University Engineering Society T-shirt, 1970s)

[Firstone18]

I agree with chrism, the 'wanderings' are what makes it such an enjoyable series to read - keep wandering as much as you like! I am now very intrigued to find out about left or right hand leading axles!
Cheers