Valve gear settings

[Hatfield Shed]

So there I was recently, explaining to a young lady how the valve gear of a steam loco effected the necessary steam distribution to the cylinder, to ensure that the engine started in the desired direction; and then how the gear could be linked up to procure more economical expansive working. This went quite well, with the aid of a little model of Mr Walschaert's gear I knocked up some years ago.

But then came the problem when I reached for some photographic examples. I have a fair selection of pictures to choose from, in common with many of us. But for all that, other than a couple of heavy mineral types starting on grades, which had pretty much full gear applied by the evidence of the valve rod in the expansion link - fortuitously one going forward, the other in reverse - the pacifics starting away, as in still a good way from reaching the ends of the KX platforms, are already well linked up; the valve rod position little further down the expansion link than on the same class running fast in short cut off.

Now the only heavy steam locos I have footplated, are since BR operated steam ceased. These were locos being worked here and there around the world, mostly near all out due to gradients and loading: started in full gear and worked in indicated 40 -50~% cut offs most of the time, the valve rod could be seen to be well down the expansion link. (Not too surprising with a couple of thousand tons to haul up a 1 in 40.)

But what cut off did the driver typically employ to get a Doncaster pacific away with a regular express out of KX? Was it just as far down as required to supply steam to start, and then quickly linked up to a pretty short cut off as soon as the wheels were turning? Because that is rather what the photos suggest.

[greenglade]

There are some table's in 'LNER STEAM' by OS. Nock that may help answer your question ...here's one table for A1 Royal Lancer on a journey from Grantham to Darlington. with a full load of 515 tons.



Here the driver is making full use of the regulator but in other table's it's interesting to note how different driver's control their trains, for example some use full regulator for the entire journey, it's either wide open or shut relying purely on the reverser for controlling the loco.

regards

Pete

[JASd17]

HS, one has to consider the 1 in 107 start out of King's Cross. No real room for expansive cut-off working. Gresley Pacific locos were limited to 65%, if I recall correctly, due to the derived 2 to 1 valve gear over-travel in the middle cylinder. Something which Mr Thompson corrected at the expense of a third set between the frames, which Mr Peppercorn continued.

Still, I am sure you were able to explain better than some modern picture books showing steam locos.

I have seen many photos claiming to show an express starting from 'x platform', when the loco is still clearly in reverse gear.

I apologise in advance if my understanding of valve-gear above is somewhat compromised.

John

[JASd17]

Sorry Greenglade, I fail to see how you are helping with the original post. Your post shows a locomotive in full-cry for the most part, although interesting that the regulator is only fully-open on the fast stretches.

The gear would be just below the mid-point of the expansion link in the latter case.

John

[greenglade]

err.. no it's not... it shows the journey from start to finish , time, speed, regulator position, cutoff position and some pressure details...I would have thought that this is what was asked for...if not then my mistake...

Pete

[JASd17]

err.. no it's not... it shows the journey from start to finish , time, speed, regulator position, cutoff position and some pressure details...I would have thought that this is what was asked for...if not then my mistake...

Fair enough, the beginning does show Full regulator and 65% cut-off.

John

[Seagull]

But what cut off did the driver typically employ to get a Doncaster pacific away with a regular express out of KX?

It just so happens that your question has been answered by a MoT inspectors report;- Accident at Kings Cross on 4th February 1945.
Go to the bottom of the page and click on the small orange coloured pdf symbol - this will download the report.

Out of interest one of the two passengers killed was Cecil Kimber - he of MG Cars fame.

The report is 14 pages long and contains quite a lot of details about Kings Cross station and operations with the heavy wartime trains.
The bit you are looking for is 'Trials' on pages 8 -10, paragraphs 21 to 25.

Alan

[Hatfield Shed]

Alan,

That's a real find, thanks for the link. And anybody else - it's well worth the reading. It's like 'For want of a nail'; the frozen sand from the pits, a sand kiln often not serviceable at KX, no time for the fitter to definitely get the engine sanders to work before coming off shed, a bad rail in the tunnels , a driver who didn't appreciate that near continuous slipping might bring the train to a halt and it then starting to roll backwards, and so on.



But for all that, it doesn't satisfactorily explain the photographic evidence of the gear settings some drivers employed! The full gear setting is what I was expecting to see, as religiously reported in the outpourings of OS Nock and others. Their 'cabbings' always report use of full gear to get started, and notching up only occurring after some distance travelled and some speed attained. But in photo after photo where the expansion link is clearly on view, and the engine has just started - still on the platform, vertical column of exhaust so no forward progress - the loco is far from in full gear.

A really clear example some may have to look at may be found in 'Eastern steam in colour' by High Ballantyne, p14, as A1 60121 'Silurian' gets away, in a photo credited to G Rixon; the loco is in nothing like full gear. What I am wondering is if some drivers realised that provided an admission port was open on one cylinder, they could get started on much less than full gear, and thus reduce the risk of a slip.

[Seagull]

If you look at paragraph 23 again, line 3 (the test without using sanding) - 'He adjusted the reversing gear to 50% cut-off'.

On a lighter pre-war train I would guess many of the drivers would do this.
The lesser blast would not pull holes in the fire so much and would also be less likely to throw cinders etc. out of the chimney in a busy station.

'Not good for customer relations Old Chap...'

Alan

[65447]

When I was studying Engineering at Peterborough Tech in the late 1960s, there was in the workshops a miniature set of valve gear, Walschaert's as I recall, mounted on a wooden base and hung on the wall. I can only recall one but there may have been another of a different type. Probably around 18" high and 48" long, each component could be adjusted to demonstrate it's function and effect relative to the others. It was labelled LNER so I presume was an educational item supplied to those colleges associated with the Company.

[JASd17]

Where does the 1 in 107 start exactly? I note the platforms are level on the diagram I have.

Therefore at the Cross could one get away with just a few yards of less cut-off with a light train, hence less chance of slipping?

Certainly not with the wartime exploits!

Just a thought.

John

[Seagull]

Where does the 1 in 107 start exactly?

If you download the MoT report I linked to above it will show you exactly.

But if you cannot, just after the signal box there is 1:100 down gradient to 51 yards inside Gasworks Tunnel to clear the underside of the Regents Canal conduit and the 1:105 up gradient starts there.

Alan

[JASd17]

Seagull,

Once again I should have looked at your link before my last comment.

If my interpretation is correct there was a chance of departing a 'normal weight' train, without slipping, using less than the full 65% cut-off. As stated by Hatfield Shed in the original post.

I know there have been doubts cast on the cut-off settings noted by footplate observers in the past, simply because the indicator was not too accurate, the driver would know by experience and feel, not a number on the scale. I wonder how footplate observers did measure cut-off, via the indicator or noting turns of the reversing gear?

John

[Seagull]

I wonder how footplate observers did measure cut-off, via the indicator or noting turns of the reversing gear?

I would think that nearly all would look at the graduations on the reverser scale, though the drivers would probably rely more on the number of turns and /or what the blast from the chimney sounded like and may well have given their opinion of the 'actual' cutoff.

When new I am sure the graduations were probably fairly accurate, my guess would be within 2-3%. As wear set in this would vary.
Post war all the engines had frame and hornblock repairs. Reversing rods had been cut in two and probably several of the major valve gear components replaced.

There is a classic comment about a worn reversing shaft on Mallard in the late 1950s early 1960s in the book LNER Pacifics Remembered -
P.N. Townend.

Page 102 - The section by F. Knight:-

'When the left hand side was in mid-gear the right side was at approximately 15% cut off and with a shunting pole for leverage the quadrant could be lifted into 15% in back gear.'

Anyone care to guess what the cut off really was?

Alan

[Hatfield Shed]

'When the left hand side was in mid-gear the right side was at approximately 15% cut off and with a shunting pole for leverage the quadrant could be lifted into 15% in back gear.'

Anyone care to guess what the cut off really was?

On average over the three engines , somewhere near 0%, which is mid gear! Better make sure that regulator is closed when on shed. No small wonder that locos sometimes 'walked' once the fire had been made up ready for the next turn.

No doubt about it, UK steam engineering practise was exceedingly rough and ready when it came to both original design and maintenance standards for the high wear out components. Steam locos would still run - well enough to keep schedule - in a condition the equivalent of which would see an IC engine 'eat itself' in moments, had it succeeded in starting. It all rather goes to emphasise that the steam locomotive was at bottom a 'cheap and dirty' traction solution. Practise in North America was the most advanced in this respect, driven by the necessity of keeping going far, far, from maintenance facilities, and it is a pity that more of their advances didn't continue to come to Doncaster after the K4 study.