Steam Loco building & design in the UK and Abroad.

[unclebobkt]

  if 'Less is more.' and 'Three cyl. good, four cyls. bad.', (with apologies.),  then why did Churchward set the GWR. on the 'Four cylinder.' path for most of its express & passenger engines?

  The only reason that comes to my mind is that perhaps four cyls. offer a smoother ride to the PAX. than three cyls.?  But looking at the cost and the weight implications, plus the additional & pre-journey maint'ce. req'd., ( the 'Castles.' &  the 'Kings.' each having more than one hundred lubrication points that needed att'n.), might outweigh what the PAX. thought.

  But then possibly the GWR. was being its idiosyncratic self and ploughing its own furrow?

 

        

[Arthur]

 

Two images of US made cast bedframes.

 

Frame for one of the 141R mikados supplied post WW2 to France

 

 

 

And a frame for a Pennsy K4 pacific.

 

 

 

I doubt that castings of such size and complexity are made anywhere today. Modern welding technology enables complex shapes to be made up from smaller components.

[jamie92208]

Those engine beds are indeed works of art and obviously the product of much development.  The actual pour must have been a fascinating process, I wonder if they used two or more ladles at the same time.   A few years ago I was involved in having cast iron wheels cast for a horse tram and the foundry was the one that cast the pieces for the half size iron Bridge replica that is at, IIRC, Blists Hill.  The main members were over 20' long and the foundry manager was telling me that they had problems with the iron flowing down the length of the mould, which was on the floor, and then the molten iron forming a wave and rebounding from the far end but solidifying part way back.   They scrapped that cast and did another using two ladles.  The size of those engine beds must have had similar problems, thought they would have been closed moulds rather than open ones.

 

Jamie

[jamie92208]

Just to add to the above, the whole process of getting the tram wheels, and many other parts such as axleboxes, made, gave me a much better understanding of the various crafts involved, from pattern making to moulding through to the actual casting.   When I look at the sheer complexity of those engine beds I am just awe struck.  The other thing that strikes me is how do you get the machining done.   It was difficult enough getting two parallel holes 12"  apart, drilled in an axlebox, weighing 25 kg, machined, let alone how you accurately machine those cylinders with all their associated fixings.

 

Jamie

[The Stationmaster]

  if 'Less is more.' and 'Three are better than four.' then why did Churchward set the GWR. on the 'Four cylinder.' path for most of its express & passenger engines?

  The only reason that comes to my mind is that perhaps four cyls. offer a smoother ride to the PAX. than three cyls.?  But looking at the cost and the weight implications, plus the additional & pre-journey maint'ce. req'd., ( the 'Castles.' &  the 'Kings.' each having more than one hundred lubrication points that needed att'n.), might outweigh what the PAX. thought.

  But then possibly the GWR. was being its idiosyncratic self and ploughing its own furrow?

 

        

 

There were some very logical reasons behind Churchward's decision to go for 4 cylinder engines for the heaviest work with some lessons learnt/observed from the French compounds.  The most important was obviously the use of more cylinder capacity to give more power but by dividing the drive over two axles that power was more smoothly delivered which gave not only a smoother riding engine but also delivered a  smoother drawbar pull to the train.

 

Whether or not Churchward considered using three cylinders is a moot point but logically two pairs of equally sized cylinders delivering power to two axles would produce a more balanced machine than using only a single additional cylinder.  And of course that layout was exactly what Stanier used for his most powerful designs on the LMS although the 3 cylinder designs also had divided drive.

 

While it is true that the oiling of GW 4 cylinder engines involved a lot of oiling points that was true of any miulti-cylindered engine unless it happened to have been designed by Bulleid - the preparation time for a 3 cylinder Bulleid pacific, much of which was time allowed for oiling, was shorter than that for many, if not all, 2 cylinder 0-6-0s.

[roythebus]

Talking of machining, I used to know someone whose job it was was to check the "truth" of the generator armatures at Dungeness power station. they had to accurate to within something like 20thou, and the shaft was over 60' long. The main problem was the actual power station bed moved up and down as the tide went up and down. Remember a loco frame is constantly moving in all directions.

[34theletterbetweenB&D]

Right, so there's nothing inherently wrong with a four cylinder layout.

 

Three became common in the UK because it was able to provide sufficient 'power' in most cases. Yes, with four you add the extra costs of build and maintenance and the extra cylinder brings with it a set of frictional losses. And, as with the BR standards, you wouldn't use four if three would do, nor three if two would do. Neither would you adopt four smaller cylinders of the same total capacity as three larger ones.

 

However, if you need, within the constraints of the loading gauge, and presuming that the boiler can meet the demand, as much 'power' as possible then a fourth cylinder surely makes sense? Cheaper than double heading.

 

Comparing a Princess Coronation to an A1,

 

PC 4 cylinders, 16.5" x 28", volume of all cylinders 2900 cubic inches with a total piston area 103.6 square inches,

 

A1 3 cylinders, 19" x 26", volume of all cylinders 2328 cubic inches with a total piston area of 89.4 square inches.

 

That is a big difference in potential cylinder output, the extra frictional loses pale into insignificance. Could Peppercorn have fitted even larger cylinders to the A1 or had the outer two reached the loading gauge? Had he 'maxed' out the potential of a three, equal, cylinder layout within the loading gauge?

 

So I'm not seeing anything inherently wrong with a four cylinder layout if the extra complexity can be justified by the need for power, is that the case?

The three isn't nearly maxxed out, there's the option for increased stroke for a start to 28" or 30" both commonly used in UK practise, if more swept volume is required without any increase in the overall width to challenge the loading gauge. But of far greater significance is the steam admission. It's the energy of the steam admitted to the cylinder that sets the limit on power output. If the Duchess delivers the power required at 15% cut off, the smaller cylinder volume of the A1 will match it at 18%. The LMS/LMR found this out with their rebuilt Scots and 2A boilered 4-6-0s, all rated class 7P. Did the same work even though the Patriot and Jubilee origin 7Ps had smaller cylinder volume.

 

The rebuilt Scot with much smaller cylinder volume than the Duchess, could short term match its power output in service if you want an 'all the same design school' comparison between three and four. The cylinder volume didn't set the limit in output for normal service. Make the cylinder volume large, and you run into the trouble of excessive power development. Duchesses and Kings couldn't be driven in the most efficient fully open regulator style most of the time: the driver had to reduce the pressure supplied to limit the power. This because the valve gears didn't perform below about 12% cut off, and were typically optimised in the 15 - 25% range. Better to have a smaller cylinder volume for efficient running under modest power demand - which was most of the time by far - and run less efficiently short term at maximum power on banks.

 

  if 'Less is more.' and 'Three are better than four.' then why did Churchward set the GWR. on the 'Four cylinder.' path for most of its express & passenger engines?

 

 The short answer is because he was an early entrant in the multi-cylinder stakes. 'Doubling up' the well understood two cylinder engine was the obvious path to increasing cylinder capacity. It also simplifies the valve gear provision, as a pair of cylinders can run off one gear by a simple reversing lever. The problem of needing an extra set of valve gear for a three (expensive piece of kit, weight penalty) is what led to experiments by various folks in a derived drive, of which the Gresley conjugated gear is the best known example. And these devices needed some time for development before they were made reliable. So if you want to make progress now with multi-cylinder development, the proven path is simplest, double up twin cylinders.

[Sheffield]

Although frames for steam engines were cast in the US for UK builders, some of the engine blocks for the American  EMD locos were cast in Leicester, England. I wonder if any are still in use.

[Arthur]

 

 

 

 

Much of what you say above comparing locomotives brings in other parameters which makes a direct comparison impossible.

 

Cylinder stroke isn't limited by the loading gauge whereas diameter is. By maxed out I was referring to diameter so, sticking to the A1, were 19" diameter outside cylinders as big as the loading gauge would allow?, therefore 3 x19" was the max? I suspect that they were pretty damned close. With a 4 cylinder design is it the space between the frames that generally limits the diameter?, probably.

 

Surely diameter (or total piston surface area) is important in its own right, greater surface area exposed to the the steam?

 

 

You seem to be suggesting that the swept volume reaches some ideal beyond which it has no benefit? You run into 'excessive power development'?? So ignoring the 'problems' with the Kings and Princess Coronations having to be eased back surely the ability to develop high power might well be the designers goal?

 

 

 

What I was/am asking is simply this, all things being equal, other than complexity, what is the issue with 4 cylinders?

 

From your original post;

 

For general purposes, Stephenson got it right: two. Only advance to three if two cannot deliver enough power. Under no circumstances have four or more (simple) in a single engine frame, unnecessary expense for a start, four plays three.

I am looking for evidence to support the claim "under no circumstances have four..." Is this referenced anywhere?

[Horsetan]

....there was a real difficulty in getting a high output loco not only within the confines of the structural loading gauge, but also within the weight limits the UK infrastructure imposed. An advance to and acceptable 25 to 27 ton axleload instead of the 22 ton limit of the UK steam period would have made the design of pacifics - and potentially 4-6-4s and 4-8-4s - much simpler...

 

....Chapelon would so loved to have had his hands on some typical US superpower. He was pretty confident he could have doubled the typical power output. .....

Chapelon was a man undermined by circumstance and internal politics, a prophet without honour in his own country. Had the French authorities not imposed a ban on new steam development from 1951 and allowed him to really get going, then his plans for things like 144s and 152s might well have taken to French rails.

 

However, I do think that - had he come to work in Britain - he would have found our then loading gauge and axleload limits annoying, since these would have constrained his ideas. If you look at his 160A1, although it proved possible to squeeze a six-cylinder system into the French loading gauge, I'm not sure that would have been workable in Britain. He would also have had to recognise that most British steam crews were not exactly familiar with the art of compound driving.

 

Even today, we only have one working mainline compound, and that's in Northern Ireland. There seems to be no prospect of no.1000 returning to steam, and as the years roll by, it becomes ever more difficult for the NRM to accord it any sense of priority. What price a new-build Compound?

[Arthur]

 

I wonder if they used two or more ladles at the same time.  

Jamie

  

 

 

Multiple, simultaneous, pours for larger castings was very common. You want to get the molten metal in as quickly as possible and some castings, because of their shape, necessitated pouring at multiple points.

 

Very large castings also required the output of several furnaces. The specialist founders tended to have furnaces with outputs somewhat smaller than the general steelmakers because most of their work was in the medium weight range, tens of tons per heat rather than 100 tons plus.

 

In the 1950s, The English Steel Corp. works at River Don, Sheffield, had three 90t acid open hearths and very large castings required all three to have refined a steel of the required specification and to be tapped simultaneously into 90t ladles, then teemed into the mould. In a reverse to the trade discussed previously they supplied a number of near 300 ton castings to the U.S.

 

The Lancashire Steel Corp. at Irlam had an active foundry trade and very large castings there were done on the floor of the open hearth melting shop rather than in the separate foundry.

 

Iron castings, which tended to be smaller, could be cast direct from the blast furnace though iron quality control would be difficult. More usually they would be made from pig iron remelted and refined in smaller cupola furnaces, more than one if necessary, and again multiple pours were common. The furnace at Blists Hill is, or certainly was, a cupola furnace. I have seen it incorrectly described as a blast furnace.

 

These days all melting, pig iron or steel, would be in electric arc furnaces.

 

 

The other thing that strikes me is how do you get the machining done.   It was difficult enough getting two parallel holes 12"  apart, drilled in an axlebox, weighing 25 kg, machined, let alone how you accurately machine those cylinders with all their associated fixings.

Jamie

 

As regards machining. My Dad and brother worked at Metropolitan Vickers/AEI/GEC in Trafford Park, Manchester. For the very large workpieces they were bolted firmly to the machine bed and the various cutting stands and arms moved around it in a calibrated motion. One of the largest they had was a ram borer in the steam turbine division, installed when I was a kid, which had concrete foundations thirty feet deep. When my brother later worked there I saw it in operation.

 

They were regular recipients of large steel forgings from English Steel, turbine rotor shafts worth a few hundred thousand pounds back then, before they were turned and had the blades fitted.

 

 

Talking of machining, I used to know someone whose job it was was to check the "truth" of the generator armatures at Dungeness power station. they had to accurate to within something like 20thou, and the shaft was over 60' long.

 

Some years earlier a turbine shaft had become unbalanced whilst on high speed rotational test in the test house at MV. It broke up and lumps of steel, some weighing a ton or so, were hurled across Trafford Park fortunately without injuring anyone. The test house walls bore the shrapnel scars until it was demolished in the 80's.

[jjb1970]

Large industrial machine tools of the scale used in environments like ship yards, power plant machinery manufacture and such like are on a different scale to what most would recognise. Alignment is a real skill and it is one of those skills that despite modern management theory does rely to a significant extent on experience as there is a lot of judgement to make calculated values work on the shop floor. You can do a lot with in-line boring but it does not work for everything and it gets more difficult when you need to factor in offset. This is a field where you can see the effects of a changed industrial landscape, European companies (it is not just the UK, none of our neighbours fare any better) really struggle to get anywhere near the standards of speed, efficiency and accuracy which is taken for granted in Korea, Japan and increasingly China. And that is simply because what is a routine job in Asia is something done infrequently in Europe.

 

On steam locomotives, by the late 1930's it should have been apparent that the technology was rapidly approaching obsolescence and that electrification and dieselisation could provide far superior performance in just about every way. Which then raises the question of how much effort is worth applying to a technology which is nearing the end of its useful life. One of the reasons I find Oliver Bulleid so fascinating is that he was far too intelligent and capable an engineer not to be aware of the inherent limitations of steam along with the potential of diesel and electric power (and when he turned his hand to it, he was quite capable of producing good diesel and electric trains) yet he threw himself into efforts to keep steam viable.

[Allegheny1600]

I'm assuming that a large cast steel frame of the sort illustrated above, would be much stiffer and stronger than a built up 'plate frame'. Surely, for very high power locomotives, this has got to be a good thing?

[jamie92208]

I'm assuming that a large cast steel frame of the sort illustrated above, would be much stiffer and stronger than a built up 'plate frame'. Surely, for very high power locomotives, this has got to be a good thing?

 

They were a lot stiffer than a plate frame.  However a few years ago I watched a video of UP 844 which had some footage taken by a camera mounted on or near the slide bars on one side.  Even with all that stiffness you could see the whole frame and wheels move a little with the piston strokes.  I'm not sure of the HP but I think that they developed over 5000 on 2 cylinders.

 

Jamie

[John_Miles]

They were a lot stiffer than a plate frame.  However a few years ago I watched a video of UP 844 which had some footage taken by a camera mounted on or near the slide bars on one side.  Even with all that stiffness you could see the whole frame and wheels move a little with the piston strokes.  I'm not sure of the HP but I think that they developed over 5000 on 2 cylinders.

 

Jamie

All structures deflect when subjected to a load. If you lean against the Empire State Building, it will deflect, the amount would be too small to measure but it would happen. Truly rigid structures don't exist. At one extreme you get aircraft which have easily detectable and relatively large deflections. At the other end you get civil engineering structures which are designed so as not to scare the users and are quite stiff - also trying to walk on a floor which deflects by more than a fraction of a mm is quite difficult.

[Arthur]

 

I always thought that one of the reasons cast frames were popular on large locomotives abroad was that they gave a bit of flex on less than perfect track (not saying all foreign track was less good than ours, just some) and being cast there were no riveted joints to loosen as the frame flexed. Unlike iron, steel will withstand a good degree of flexing.

 

Plate frames being very rigid, certainly in the vertical plane, and having riveted cross members, were best suited to use with top quality track work?

 

Could be wrong.

[34theletterbetweenB&D]

...I am looking for evidence to support the claim "under no circumstances have four..." Is this referenced anywhere?

 You need to have studied value engineering under a dreadful humorist. This was always the challenge: accepted custom and practise insists on 'n' of this component. Under no circumstances have 'n'; I should have gone on to complete the tenet: (n-1) is a pretty weak target too.

 

Much of what you say above comparing locomotives brings in other parameters which makes a direct comparison impossible.

 

Cylinder stroke isn't limited by the loading gauge whereas diameter is. By maxed out I was referring to diameter so, sticking to the A1, were 19" diameter outside cylinders as big as the loading gauge would allow?, therefore 3 x19" was the max? I suspect that they were pretty damned close. With a 4 cylinder design is it the space between the frames that generally limits the diameter?, probably.

 

Surely diameter (or total piston surface area) is important in its own right, greater surface area exposed to the the steam?...

 

 Diameter is only one of two necessary variables that go to define the power potential of a cylinder in combination with the varying pressure during that stroke. It is volume - and specifically the effective volume swept, (swept volume less clearance) - that limits available power per stroke.  Consider a cylinder of any diameter you like, but no stroke = no power. Likewise a cylinder of no diameter, but infinite stroke = no power. The product of these variables - volume - is what is required for power production.

 

At least 21" diameter outside cylinders were possible for the LNER, in the form of the P2, which shall hopefully once again be seen in action. Where the limit lies on outside cylinder diameter for a UK railway loco is unexplored territory. I should think anything up to circa 30" diameter straight across might be possible, with some clever work with framing; probably a cast one piece frame would be the way to accomplish that.

 

The piston surface area with the applied pressure only defines static force. This is mightily confused in many minds with power, but the two are not equivalents in any way. Force x distance (piston area x stroke in the case of a piston in a cylinder) is power, with the missing term being the effective pressure during that stroke; thus the reason why it is volume of the cylinder that matters.

[runs as required]

 ...Where the limit lies on outside cylinder diameter for a UK railway loco is unexplored territory. I should think anything up to circa 30" diameter straight across might be possible, with some clever work with framing...

Interesting point (as ever with your posts)

 

Which puts me in mind of the Crab again. I understood its cylinders were raised to comply with the CCE's requirement to clear platform edges - but by the time Stanier's version was on the drawing board, this was deemed unecessary 

Were cylinders to be raised, would greater diameters be possible within the loading gauge, accommodated alongside the lower half of the smoke box?  Could one achieve a feasible inlet/exhaust circuit with such an arrangement  - say If piston valves were underneath?

 

About all this new re-creation of long lost loves - including the P2, a Patriot, even a Standard 4-6-0, I do find it a shame that no new locomotives are being constructed embodying fresh thinking about 'unexplored territory.'

The Porta project died; does anyone know anything about this link ?

 

dh

[Arthur]

You need to have studied value engineering under a dreadful humorist. This was always the challenge: accepted custom and practise.....

 

 

Thanks, and yes, I fully understand that a piston without stroke does nothing though diameter and stroke each contribiute some unique properties to the equation.

 

However, none of this answers my simple initial query seeking clarification on why "under no circumstances have four...."? Or is that the product of the dreadful humorist?

[cheesysmith]

When you start talking about multi cylindered steam loco's in the uk, you have to start to consider the restrictions imposed by bridges, and then consider the hammer blows on the track from the masses at work in the balance weights, rod, thrust from the pistons themselves. All these forces are reduced with multi piston loco's, as the same power is spread over more cylinders, thus allowing a higher static axle load. The highest axle load on the LMS express loco's was the turbo motive, because it had very minor reciprocating masses. But before you start going on about more cylinders are better, you run into other problems, like making the frame strong enough to take the forces and loads involved but allowing enough physical room for the extra cylinders (again, certain multi cylindered LMS loco's had to have the front of their frames replaced during works overhaul).

 

The steam loco in this country was always a balancing act between the masses involved, the loading gauge, and especially the limits set by the bridges.

 

I agree in that the use of a non condensing turbine loco should have been explored further. I also remember reading that one of the problems with the hush hush was the pulses from the pistons caused problems with the boiler, as the boiler had been designed to be used with turbines. How would the hush hush have been if fitted with a non condensing turbine drive, just like the turbo motive?

[Sheffield]

There is an interesting book about LNER "Hush Hush" loco which suggests the problems with the loco while on test arose because of a simple mistake with the steam supply to the injectors and other auxiliary items. It was insufficient and the loco could not maintain water levels when working. By the time that was resolved the loco had already acquired its bad reputation. The other thing was that it was specifically designed to the equal of an A1 Pacific. By the time it was in service things had moved on and it was not equal to an A3.

Nigel Gresley seems to have had a liking for new things but then lost interest. For a first try the loco seems to have been a success; of course the boiler lasted into the 1960s, and was scrapped only because it was redundant.

It has been said that if George Stephenson had risen from his grave and been able to inspect a 9F the only thing that would have surprised him would have been its size, and he would have easily understood how it all worked. What more do we need to say about steam loco development?

[asmay2002]

To quote Professor Tuplin

 

"within British restrictions, the virtues of 3 cylinders and four cylinders were about evenly matched.. Four valves could be served by 2 valve gears and rocking levers, Three cylinders needed either 3 gears or 2 plus a conjugating mechanism that needed more careful maintenance than sufficed for rocking levers. "

 

"Station platforms limited outside cylinders to 22" in diameter". 

 

"With axleboxes in mind the largest desirable diameter for (a pair of) inside cylinders was 20".

 

"the greatest total volume of 4 equal cylinders was about 10% more than for 3 equal cylinders.  Four cylinders need not be equal but British design rarely took advantage of this fact."

[Grovenor]

Which puts me in mind of the Crab again. I understood its cylinders were raised to comply with the CCE's requirement to clear platform edges - but by the time Stanier's version was on the drawing board, this was deemed unecessary

Hughes kept to a low boiler pressure and hence needed large cylinders,(180psi, 21"dia) the change made by Stanier was to increase boiler pressure and thus reduce cylinder diameter (225psi, 18"dia) for the same tractive effort. The smaller cylinders could be set lower. No-one moved the platform edges.

Regards

[Arthur]

To quote Professor Tuplin

 

"within British restrictions, the virtues of 3 cylinders and four cylinders were about evenly matched.. Four valves could be served by 2 valve gears and rocking levers, Three cylinders needed either 3 gears or 2 plus a conjugating mechanism that needed more careful maintenance than sufficed for rocking levers. "

 

"Station platforms limited outside cylinders to 22" in diameter". 

 

"With axleboxes in mind the largest desirable diameter for (a pair of) inside cylinders was 20".

 

"the greatest total volume of 4 equal cylinders was about 10% more than for 3 equal cylinders.  Four cylinders need not be equal but British design rarely took advantage of this fact."

Thank you very much for that Andy. It would seem then, that there might well be advantages to adopting four cylinder in some circumstances. That was really all I wanted to clarify.

[bike2steam]

I was always led to believe that 4 cylinders was best for balance at prolonged high speeds. Given Staniers 'upbringing' at Swindon, I'm surprised he didn't use rocking-shafts on the Princess-Royals especially with out-side valve gear, and not waiting until the Coronation class. The Bulleid original pacifics, in theory, were supposed to be near enough perfectly balanced and hammer-blow free BUT when the locos became well worn the theory was 'blown out of the water', as was proved by 34105 at Swanage during it's visit in 1988. The same could be said about Gresleys conjugated valve gear, that could quite often be troublesome and deliver an odd 'out of tune' exhaust beat.