Inside valve gear

242A1's posting on the Gresley V4 thread, http://www.national-preservation.com/threads/gresley-v4.802580/page-4 post #80, highlights the large number of choices to be made in designing a steam locomotive. One of them is whether to put the valve gear inside or outside the frames.

Outside valve gear has some obvious advantages: notably that return cranks are easier than eccentrics to assemble and disassemble, and better accessibility for oiling up. So why did the GWR persist with inside valve gear? Did they use it on the 2-cylinder engines only because they thought outside Stephenson's wouldn't fit (disproved by LMS 4767), and on the 4-cylinder engines only as an obvious development from the original scissors gear? Or does it have some other advantage?

 

I don't think it was only the GWR who persisted with inside valve gear - even the rest of the 'Big Four' made many locomotives with inside valve gear, particularly with the smaller engines - look at the many 0-6-0s, both tender and tank engines that were built right through to nationalisation with inside gear. As to why, I don't know with certainty if it was only a case of "That's the way they've always been built." or if there were other more practical reasons - for example with inside valve gear did it shorten the distance steam had to travel from regulator/valves/cylinders/valves/exhaust?

It seems that it was only with the coming of the BR standard loco range that outside valve gear was to form the norm - albeit for a limited time!

 

Don Townsley in "The Hunslet Engine Works" states that inside cylinder engines were cheaper to make than comparable outside cylinder ones (see page 87). The same probably applied to main line locos.

 

I have read that inside valve gear was preferred for shunting engines as outside was thought to be a risk to trackside staff such as shunters.

Having said that most of the rest of the world didn't seem to share that concern

 

Simple inside cylinder engines make a lot of sense in some contexts, you can often get a very compact arrangement because the cylinders don't need to clear the wheels, only the axles - see Adams changing from outside cylinder 4-4-2T classes to inside cylinder 0-4-4T classes when he needed to get more power from the same size. The actual power unit of an O2 (cylinders, drivers, valve gear) is extraordinarily compact. The cylinder block also provides a handy bit of frame bracing, although perhaps the need to leave room for the connecting rods and motion then taketh away...

I've always seen the GWR adherence to inside valve gear on outside cylinder engines as the result of a very strong culture of standardisation, coupled with Churchward laying out the templates for all future classes before the general ascendancy of outside valve gear had really taken hold; the progenitors for the major GWR lines of development (2-cyl and 4-cyl 4-6-0, 2-6-0, 2-8-0, large and small 2-6-2T, 2-8-0T) were all in service by 1910. A lot of engines entering service on the other lines around this time had outside cylinders and inside valve gear: various Atlantics, a lot of GCR and LBSCR classes and plenty more, but they were nearly all developmental dead ends in the post-Grouping world. I think at the time there was still a hangover from the Victorian desire to keep the working parts covered up as much as possible, and a tendency to not consider labour cost and ease of servicing as significant factors.

After 1910, but before 1920, Gresley (H2/K1), Urie (H15) and Maunsell (N) had between them put into service the progenitors of the modern outside valve gear 2-6-0 and 4-6-0, but they were all starting from a base of essentially Victorian motive power. Strikingly, none of their railways subsequently produced a new class with outside cylinders worked by inside valve gear (edit to add: I have just realised that this statement is proved wrong by a mere 140 locomotives on the Southern, built to the designs of a certain O.V.S. Bulleid). The LMS was a bit of a mess until Stanier was appointed and promptly adopted outside gear for outside cylinders across the board, despite his GWR roots.

Although the GWR gears generally gave good valve events, I don't think there's any reason they couldn't have been reproduced with outside gear; outside Stephenson's gear was certainly found in French practice long before 4767 saw the light of day.

 

If you are using a link gear, such as Stephensons, it is quite difficult to put it on the outside and keep it within the British loading gauge because it has two eccentrics to accommodate. It can be done, as was proved with 44767 but outside link valve gears were never common beasts, especially in the larger sized locos. Why the GWR went for inside Walschaerts for the Castles & Kings, though, I never did understand. Perhaps it was also related to loading gauge although I can't see it.

 

I should have made clear that I was enquiring about inside valve gear with outside cylinders. If you choose inside cylinders (for whatever reasons) it would be odd to use outside valve gear, though we have seen one instance of that here recently, at http://www.national-preservation.com/attachments/_1000283-jpg.22851/ briefly discussed at http://www.national-preservation.com/threads/adriatic-steam-express-9th-sept.789993/

 

re GWR designs, Churchward had a strongly held aversion to outside valve gear or inclined cylinders. This is often quoted in primary souce stuff.

Only with Hawksworth's pointless 15xx class was this tradition changed nearly 25 years after Churchward retired, except for the example of some steam Railmotors and the narrow gauge Vale of Rheidol locos.

Cheers,
Julian

 

Many Victorians disliked outside valve gear for purely aesthetic reasons. I feel sure I recall a quote from a Victorian CME that outside valve gear looked like " a boy running with his trousers round his ankles" As to the Castles and Kings, fitting two eccentrics per side plus two crank pins may have been seen as too tight a squeeze. Walschaerts only requires one eccentric per side.

 

That quote is alleged to have been made by Patrick Stirling regarding express locos with coupled wheels.

 

Why do you think the 15xxs were pointless? I have extensive experience of firing and driving 1501 on the SVR, the latest being last Sunday. It is relatively comfortable, easy to prepare and dispose, steams like a witch, runs surprisingly smoothly for such a short wheelbase engine, and is very powerful.

What's the problem?

 

As regards the original question, I have always thought, with the GWR, that they placed the gear inside for aesthetic reasons, although, I stress, I do not know that.

 

Hi jtx,

My comment on the 15XX class was that they were pointless because there were many other locos in abundance at the time that could have pulled carriages from Old Oak Common to Paddington and vice versa quite easily. The 57XX springs to mind and fitted the bill.

The 15xx remains an enigma. I do not doubt it was a good design for what was intended, or that 1501 performs very well on the SVR. Whether the expense was justified is quite another matter! And why do you need a loco with non standard outside cylinders with piston valves and no superheaters?

Cheers,
Julian

 

Not being a GW aficionado, I've no idea of the ins and outs of that railway. However, the 57XX's and their lot were a design well over fifty years old. There comes a time when you have to look afresh and bring things up to date, no matter how tried and tested the earlier designs were. That, I suggest, is what Hawksworth was doing. It wasn't a big class because you rarely do that with a prototype design. If things had been really different and internal combustion wasn't a mass option, I would suggest that, today, we would have hundreds of 15XX tanks and no 57XX tanks. We would also be looking for a replacement of the 15XX by now. The fact that internal combustion came to the fore, both on rail and road, changed all that. Crystal balls are very handy things but very, very few people have them.

 

There is more to the inside valve gear than just the aesthetics.

When Churchward developed the new generation of locomotives he was very thorough and studied both American and French locomotive practise in detail and copied what he found good. Part of this was the purchase of the French locomotives, maybe he would have bought US locomotives as well if they would have fit the profile?

The interesting thing is that US and French locomotive practices were as far apart as anything could be. French sewing machines versus American “tractors”.
But all the new GWR locomotives were firmly based on this study.

The two cylinder locomotives all followed the general American practice at the time: inside Stephenson valve gear and the cylinder block in two halves combined with smoke box saddle and outside cylinders and valve chests. At the time these features were universal on US locomotives. (Although the valve gear was to change quickly with the advent of the superheater.)

For the four cylinder locomotives Churchward followed the French practise (although he skipped the compound). It was intended to use the Churchward scissors gear (which has to be inside), but it was so complicated to adjust that it was quickly replaced by a conventional Walschaerts in the same position.


Could recommend Gibson’s book "GWR Locomotive Design".

 

Having spent many, many, really, many hours since 1982, "in between" oiling up Stephenson link motion, although, to be fair, my firemen usually do this nowadays, as I did for my drivers for all those years, I feel well qualified to comment on inside motion. It is relatively easy to oil up, although occasionally difficult and messy to do. On Panniers, you can do a lot from the footplate framing, with some contortions; on Manors and 28xxs, you can slide under the boiler and do the lot, indeed, you can do it without a pit; in fact it is easier. You just stand on the track and it is like pouring tea out. And, you can't do that on the bigger boiler enines like Halls, Castles and Kings.

Contrast this with a picture in one of Oliver Winston Link's magnificent pictorials of the last couple of years on the Norfolk and Western Railroad. It is a night shot of a fitter at Shaffer's Crossing depot. He is walking alongside one of their stunning Y6B Mallets, with a grease gun on an overhead wander lead. The caption said he could grease one of these enormous double engines in 20 minutes!

You would have to be Billy Whizz to manage that on an inside motion engine, and on most outside Walschaerts's engines too. 1501 is easy to prep, but it takes longer than 20 minutes, inless you miss stuff.

Regards,

jtx

 

With the 4 cylinder locos if you go with the "Princess" set up you have both inside and outside gear, so more work. The position of the outside cylinders make the outside gear driving the inside inaccurate, as the expansion of the ouside valve spindle as its temperature rises will make the inside valve timing change. The "Duchess" layout works because the outside cylinders are further forward so the rocker arm works on the "cold" end of the outside valve spindle.

Rob

 

Exactly so. Outside valve gear driving the inside valves couldn't be fitted to the GWR 4 cylinder locomotives without either a very major redesign or accepting inaccurate events on the inside cylinders with expansion of the rods. Mechanically the inside gear was in many ways a more elegant solution. With the two cylinder locomotives its argued that there are advantages too, for example easy access to the rods without valve gear in the way.

Gibson... what he has to say is always interesting, but some of his conclusions, especially his ideas about what ought to have been built, simply don't add up.

However I suspect one reason for not changing was that with the GWR working practices of the time there was very little in the way of savings to be made.

 

Elegant in aesthetic terms perhaps, elegant in engineering terms - depends if you think ease of maintenance is part of the engineering design

 

I believe the 15xx hawksworth panniers were inspired at least by the WW2 USA dock tanks, like a GWR version

https://en.wikipedia.org/wiki/United_States_Army_Transportation_Corps_class_S100