Sir Nigel Gresley - The L.N.E.R.’s First C.M.E.

It's really fascinating to see all the different variations, and the only thing I can observe is that the W1 remains the first - maybe only? - of the Yarrow type boilers fitted to a railway locomotive in this country (there were a few prior American examples).

 

Below is a cross section of a typical Sentinel boiler.

Edit: It seems my previous picture didn't work, even though it showed on my screen. Try this:

 

Try this link https://steamautomobile.com:8443/ForuM/file.php?1,file=2738

 

I don't think Gresley makes any claim to streamlining in his paper on the loco to the IMechE in 1931. The comments that he makes about the wind tunnel testing (to study smoke lifting) are included in the attached extract. I am not sure by that omission [?] one can say the thought had not occurred to Gresley but it was perhaps not important to him in the context of the paper he was giving and/or he may also have been reluctant to make such claims bearing in mind that the lowering of air resistance does not seem to have been an objective of the experiment or design. The loco certainly had some novel features which Gresley wanted to talk about including of course the boiler and also the unusual valve gear whereby he devised a way of altering the cut-off on the inside hp cylinders independently of the lp even though there were only two sets of valve gear and the hp cylinders were driven through a rocker.

The streamlining claim of course appears in Locomotives of the LNER, and interestingly is also made by Windle in a lengthy contribution to Holcroft's paper on smoke deflectors in 1941 (extract attached).

Windle in his contribution also noted the hp saving of streamlining (which I think was referred to upthread) and noted that this data was from Gresley's presidential address to the IMechE (the paper says 1934 but it was 1936) - also attached. Gresley described the experiments (on a model of Silver Jubilee and an "ordinary" Pacific) as being "to determine comparative head-on wind resistance and to calculate the hp required at various speeds to overcome air resistance".

 

Another interesting thing - I had always (wrongly) assumed as a four cylinder locomotive that Gresley had provided four sets of valve gears, but in reality the W1 is a sort of four cylinder conjugated locomotive, if that makes sense?

 

Its a bit of stretch to describe a 4 cylinder layout with rockers as conjugated I think. The point of conjugated gear was that it mechanically added motion from two sets of gear to provide the correct movement for the rest. A four cylinder layout with a rocker between one outside and one inside cylinder each side didn't have the mechanical addition that justified the word conjugated. I don't think there was ever a standard gauge 4 cylinder conjugated gear, although Holcroft proposed one to permit 135 degree crank intervals. AIUI the problem was that the 4 cylinder implementation was very little simpler in terms of components and especially bearings than having 4 separate sets of gear.

 

That's fair Jim, I am still getting my head around the concept. So is this closer to GWR practice in some respects, like on the King's?

 

And numerous others. I don't suppose the GWR were the first to use rockers, it was an obvious enough solution. But what the GWR did do differently was to introduce some very trick and subtle geometry to make the valve events more even.

 

The Holcroft valve gear was mentioned on the Advanced Steam Technology page on Facebook (screenshot attachment). I
believe the only application of it was to the 2.5" gauge loco Tugboat Annie built by LBSC.

Sent from my SM-A105FN using Tapatalk

 

I believe that rocking shafts were used on Manson's one-off 1897 design of 4-cylinder 4-4-0 for the G&SWR, also on the Webb LNWR 4-cylinder compounds built in the 1897-1903 period.

De Glehn 4-cylimder compounds had 4 sets of valve gear, but some of the other Continental European types of 4-cylinder compound made do with two valve gears plus rockers, including most of the French PLM types built from the late 1880s.

 

As Jim says, I don't think you would generally call this conjugation. In the case of 10000, the rocker acts in a vertical plane (like the GWR (outside) 2 cylinder gear rocker). In the attached elevation drawing from the paper, just in front of the slidebar support in the lower diagram (of the outside motion), you can just make out the dotted outline of the inside expansion link, with the rocker transmitting the movement from the outside radius rod. Quite how this drive worked is not clear to me - did the inside expansion link pivot at the top on the basis it did not need to have upper and lower quadrants, and was just effectively an extension of the rocker, as the reversing (as distinct from cut-off variation) was done in the outside gear? The plan view in the other drawing shows the long bearing (like a GWR two cylinder loco) taking the drive inside. The inside gear had its own combination lever.

The King arrangement took the drive from the valve crosshead at the rear of the inside valve chest direct to the front of the adjacent outside valve chest. The King's rocking lever is a bit of a mystery as it is cranked and of unequal length each side of the central bearing. It would be interesting to get an explanation of quite what this arrangement did in terms of the motion. Martin Evans simply says that this was because of the conflicting angularities of the inside and outside connecting rods, which may be correct but is not very helpful. In simple terms, I suspect that cranking the lever will mean that the two resultant fore and aft motions are not equal, and the unequal lengths also have to be taken into account (although that seems to imply that the desired motion could not be achieved simply through making the distance each side of the bearing unequal - unless perhaps the cranking was necessary because of the relative positions of the desired connection with the valve rods?). The LMS apparently thought this too complicated and use a straight equal lever on the Duchess and decided that if you averaged the valve events in adjacent cylinders they were pretty good, even if individually the front and rear cut-offs were rather unequal.

 

Don Ashton had a bit to say on the subject here:-
http://www.donashton.co.uk/html/more_cylinders.html
Unfortunately I think you (or at least me) really need to play with one of the valve gear simulations and have a better understanding of how it all works in order to understand what he had to say.
If I've grasped thing correctly the fundamental issue is that at 50% piston travel the wheel is not quite at 25% rotation. The valve gear may be set up to cope with this 'error', but if it is then a 180 degree rocker doubles the error on the opposite valve. If you don't have equal length rods then that adds a further complication. The GWR seems to have had an especial preoccupation with really even valve events, whereas the LMS was more "**** it that'll do". That might just reflect that the GWR had an engineer, W.H.Pearce, who could actually handle the highly complicated geometry and calculations involved before computer assistance. But steam engines are like computer networks, they still work when they are a long way from right, so maybe the GWR was being over fussy. The Stars and Castles also had a cranked rocker lever, but apparently the layout was improved on the King. Personally I'm not mentally equipped to judge!

 

Thanks. I did have a play with the basic Walschaerts programme before but it produced nonsensical results at which point I gave up. You do need an awful lot of dimensions if you are modelling a gear from scratch. I have not come across Dockstader's programme for the King before. Ashton's comments about the A1 gear are interesting. I wonder if this was corrected on Tornado?

 

I think the best way to get the valve gear simulation to work is to put in the dimensions in from an existing full size or miniature loco design, then you can alter dimensions and see what the effect is.

Sent from my SM-A105FN using Tapatalk

 

This is fascinating, thanks for posting those drawings!

I think what this system allows is cut-off biasing rather than full independent variation, and may in fact have a bit to do with some of the early issues of the W1.

So the inner expansion link is driven via the rocker off the front of the outside radius rod. The rocker provides the 180 degree phasing necessary for a conventional four-cylinder loco, at least in conjunction with the inside combination lever. It could just be a rocker and it would still work. But because you also have the expansion link, the inside cut-off can be reduced relative to the outside by effectively reducing the lever length. So significantly more sophisticated than the GWR rocker levers, not that a 4-cylinder simple needs that.

Crucially, though, significant increase in inside cut-off is harder to achieve; this system delivers HP cut off as a proportion of LP cut-off, with the proportion set by the die block position in that inside expansion link. I never understood why the W1 was later modified to give 90% HP cut off, you'd simply never need that even for starting. But now I think I get it; this inside expansion link was extended to amplify the outside radius rod movement, so then they could run with say 60% HP and 45% LP cut offs. If you look at some of the details of French compound working, that wouldn't be an outrageous operating point. If your LP cut off is too long relative to the HP, the receiver pressure drops, work is poorly split and the engine is neither as efficient or as powerful as it could be. I suspect as built that combination of cut-offs simply wouldn't have been available.

 

As far as I am aware the valve gear used on 10000 was unique and never repeated. As the previous post has said there was a half expansion link to work the inside valves driven off the outside radius rod. Thus reversing the engine was through the outside expansion link and the inside half link enabled the inside cut off to be varied to be longer or shorter than that outside, hence maximum inside cutoff 90% and outside 75%. A very neat arrangement for varying the two cutoffs independently without incorporating a complete inside gear, but one oddity is that it is not possible to give a direct indication of the inside cutoff as it is that of the outside cylinders magnified or reduced by the effect of the inside half expansion link.

 

In that arrangement, the inside cylinders have most of their own valve gear, only lacking their own radius rods. That's very different from conjugated gear or GWR (etc) rockers, where everything up to the drive to the valve spindles is shared.

Edit: but a clever arrangement to allow different cutoffs, as explained in post #1215.

 

Good contribution. Gresley refers to the rocking link having a "slot and die-block", and (in response to a question) that the cut-off in the HP could be from 30% to 85% when the LP was set at 60%. So as I think you are saying, this implies that the slot part was longer than the upper part of the link above the bearing to enable it also to multiply the outside radius rod movement. Gresley's views on appropriate cut-offs seem to be slightly controversial but I guess generally compounds did not have such a high pressure.

 

I may misunderstand your point, but the inside gear has a radius rod which is driven by the "half" expansion link / rocker slot. They lack their own eccentric drive through the return crank/eccentric rod. And yes, it is different from a King.

 

Don't disagree with that but unless you are using model engineering drawings to review LBSC's etc designs (which may be the most common use - incidentally I see that Trevor Shortland's 7 1/4" gauge King has a straight rocking lever, albeit the ends are offset in the vertical plane - which the originals may be), it is difficult to get all the dimensions you need from the (available) original drawings. You can interpolate of course but that could mean building in inaccuracies in what are quite sensitive dimensions. The loco I chose to model was a bit challenging as it is a Chinese loco. I had most of the dimensions but not all (strangely, finding out technical info on Chinese locos is in some cases easier than for British locos as there are published lists of valve gear dimensions for most classes whereas trying to find out even basic stuff like piston valve diameter and lap and lead for many British locos is not easy.)