Steam loco cylinders - more is better

[ciderglider]

When reading about steam locos, I have got the impression that 3 or 4 cylinders are better than 2, at least for express locos. The argument seems to be that the extra cylinders make things smoother. Also having more than 2 cylinders means the outside cylinders can be smaller, to fit the loading gauge. But this comes at the cost of complexity, which I suppose is why Riddles designed the Britannnias with just 2 cylinders. What I've never really understood is why some designers opted for 3 and others for 4. And why never more than 4?

[Flying Pig]

I once read the first few pages of Chapelon's La Locomotive a Vapeur (in English translation). He was clearly unconvinced that more than three cylinders were ever necessary and referred specifically to GWR and LMS practice.

[kevinlms]

1 hour ago, ciderglider said:

When reading about steam locos, I have got the impression that 3 or 4 cylinders are better than 2, at least for express locos. The argument seems to be that the extra cylinders make things smoother. Also having more than 2 cylinders means the outside cylinders can be smaller, to fit the loading gauge. But this comes at the cost of complexity, which I suppose is why Riddles designed the Britannnias with just 2 cylinders. What I've never really understood is why some designers opted for 3 and others for 4. And why never more than 4?

More cylinders means more to maintain.

 

But it is not true to say 'never more than 4'. Some Garratts had 6.

 

https://en.wikipedia.org/wiki/NZR_G_class_(1928)

 

https://en.wikipedia.org/wiki/LNER_Class_U1

 

Neither type were Garratts finest hour and actually built against advice from Beyer Peacock.

[LMS2968]

'Necessary' and 'Desirable' aren't always the same thing. Design of anything, including steam locomotives, is always a compromise, and each configuration, two, three and four cylinders has its own advantages - and disadvantages. Robin Riddles went for the simplicity and ease of servicing / preparation of two outside cylinders, but needed three to get the power for a Class 8 Pacific. This also gives more even torque, but four cylinders give better balancing and help eliminate weights and hammerblow (yes, I do know about Bulleid's system). It all depends . . .

Edited July 10, 2023 by LMS2968

[Andy Kirkham]

1 hour ago, Flying Pig said:

I once read the first few pages of Chapelon's La Locomotive a Vapeur (in English translation). He was clearly unconvinced that more than three cylinders were ever necessary and referred specifically to GWR and LMS practice.

Although Chapelon designed a six-cylinder machine https://fr.wikipedia.org/wiki/160_A_1

[Wickham Green too]

2 hours ago, ciderglider said:

... 4 cylinders ... make things smoother. ...

As stated by LMS2968 4 cylinders should reduce hammerblow but they won't make any difference to torque unless the cranks are arranged to give eight exhaust beats per revolution ...... yes even more complicated and only applied to one 'production' class of loco that I'm aware of.

[melmerby]

1 hour ago, kevinlms said:

 

But it is not true to say 'never more than 4'. Some Garratts had 6.

https://en.wikipedia.org/wiki/NZR_G_class_(1928)

https://en.wikipedia.org/wiki/LNER_Class_U1

 

Neither type were Garratts finest hour and actually built against advice from Beyer Peacock.

6 cylinders on the U1 because each engine had a standard Gresley 3-cyl 2-8-0 layout (O2)

Whether it actually needed 72000lbf+ TE for it's designated job is another matter.

2x O1 would still have given 65000lbf TE and two less cylinders to look after.

[melmerby]

24 minutes ago, Wickham Green too said:

As stated by LMS2968 4 cylinders should reduce hammerblow but they won't make any difference to torque unless the cranks are arranged to give eight exhaust beats per revolution ..

AFAIK you can't do away with two sets of valve gear and use rocker shafts if you do that.

GWR Inside gear with outside rocker driven valves and LMS Coronation outside gear with inside rocker driven valves.

[jim.snowdon]

18 minutes ago, melmerby said:

AFAIK you can't do away with two sets of valve gear and use rocker shafts if you do that.

GWR Inside gear with outside rocker driven valves and LMS Coronation outside gear with inside rocker driven valves.

And a certain Midland Railway 0-10-0, which had 4 cylinders but only two valve chests, each valve feeding two cylinders that worked 180 degrees apart via crossed steam passages. :)

[ciderglider]

1 hour ago, Andy Kirkham said:

Although Chapelon designed a six-cylinder machine https://fr.wikipedia.org/wiki/160_A_1

That is quite something, but the Wikipedia entry suggests it wasn't a great success. I wonder if Chapelon came up with his "three's enough" maxim after seeing this loco in action?

[34theletterbetweenB&D]

Chapelon's 'Steam Locomotive' (La Locomotive a vapeur) needs to be read very closely to understand him on this (and most other points). In brief, cylinders and valves, and the gear, rods and the rest of the driving mechanism are expensive components and heavy: so as few as possible consistent with sufficient power development, the need to stay within the moving gauge envelope, and to keep loads on rail and structure within the civil engineer's limits (on the latter subject most forceful in his regrets in Europe compared to North American practise). In this and all other matters he is the consumate engineer, recognising the necessary trade offs for an effective and economically viable machine.

 

More than three cylinders, compounding was typically his reason, for higher powers it is problematic to keep the cylinder count down while providing  sufficient LP volume.

[The Johnster]

It's cheating to cite Garratts as having more than four cylinders, as they are two engines fed by a common boiler; none had more than four on any one of the engines ('engine' in this sense means the cylinders, pistons, inlet and outlet valves, crosshead, conrods, and small & big end bearings.  This engine is a component of the complete locomotive, in conjuntion with the firebox/boiler/smokebox assembly, frames, running plate, and wheels).  A conventional Stephensonian locomotive needs at least two cylinders driving cranks offset at ninety degrees to avoid 'dead centre' starting problems the ends of the piston travel, but it means that, at some points on the driving wheel revolution, the hard work of starting the loco falls on one cylinder until the wheel turns a bit.  3- or 4-cylinder formats avoid this, and make starting much easier, as well as having advantages around the issues of hammer-blow, ride, and increasing the total capacity of the cylinders within the loading gauge, an issue particularly pertinent to UK railways.  Running heavy trains at high speeds needs a lot of power, and as this is determined by cylinder capacity amongst other things, more than two cylinders can be an advantage for heavy express work and heavy mineral haulage. 

 

Compounding, popular in the late grouping era, also lends itself to multi-cylinder formats.  But the more cylinders you have, the more carefully you must set the loco up to give maximum efficiency, shown by even exhaust beats, and the less room you have to get in under the frames to service the inside cylinders, which are squeezed in to achieve maximum size.  It becomes a cost-effective analysis issue, as the purpose of a railway locomotive is to haul the load to time as cheaply as possible in the interests of overall profitability, so there now becomes a case for the increased availability and decreased preparation time of 2-cylinder engines.  

 

It is interesting to note that no new 4-cylinder design was introduced in the UK after the Stanier Coronation class, which was justified by being used on high-profile services with a large amount of first-class accommodation, and only one new 3-cylinder design introduced after WW2, and that an opportunist replacement for an 8P destroyed in a collision.  Plenty of new builds and rebuilds of older designs, but DoG was the only new design produced after the Bullied pacifics with more than two cylinders, as the cost-efficiency analysis was then supportive of engines that could be easily maintained and quickly prepared by a poorly staffed and ill-maintained post-war railway.

 

The WR was still building enlarged Churchward 4-cylinder engines, Castles, in 1950, but these can be regarded as an anomaly, shortly to be replaced by 2-cylinder Britannias.  There had been a 2-cylinder intended replacement for the Castles, the Hawkworth Counties, but these had been disappointing in service.

 

'More is better' is simplistic, and in reality 'better' depends on circumstances, what you want the loco to do and how much profit you want it to make for you; passenger demand, fuel costs, overall profitability, ease of maintenance/preparation, axle load, and ride.  Ride is more than a consideration of crew comfort, as a badly-riding locomotive will need more maintenance, as will the tracks it runs on, and has a safety implication in regard to crew fatigue.  Like most things about big express locos, it's a matter of balancing all these factors, and while he can design out as many problems as he can, there will often be something that arises in traffic experience that defeats the best intentions of a CME.

Edited July 11, 2023 by The Johnster

[ciderglider]

Peppercorn's Pacific's came after Bulleid's, and had 3 cylinders, but one might not consider them entirely new designs.

[Wickham Green too]

3 hours ago, The Johnster said:

... A conventional Stephensonian locomotive needs at least two cylinders driving cranks offset at ninety degrees to avoid 'dead centre' starting problems the ends of the piston travel, but it means that, at some points on the driving wheel revolution, the hard work of starting the loco falls on one cylinder until the wheel turns a bit.  3- or 4-cylinder formats avoid this, ...

Unless it's set up for eight beats to the bar - the Lord Nelsons - a four cylinder loco is just as prone to 'dead centring' as a two cylinder one.

[LMS2968]

Some LNWR Claughtons got 135 degree cranks too.

[The Johnster]

36 minutes ago, Wickham Green too said:

Unless it's set up for eight beats to the bar - the Lord Nelsons - a four cylinder loco is just as prone to 'dead centring' as a two cylinder one.

 

Yes, for each individual cylinder, but the two offset-cranked cylinders' conrods will be both pushing and pulling the loco forward simultaneously at starting, exerting a more evenly balanced force.  The Lord Nelson solution is better, but there is a down side; there is an awful lot of exhaust steam and gasses to get rid of on a more continuous basis at a relatively low exhaust velocity, resulting in the very large diameter blast pipes and Lemaitre chimney, and a need for smoke-lifting (mind you, this was a common feature on a lot of 20th century big engines where the smokebox diameter only allowed a very short chimney and smoke and hence the problem of smoke and steam hanging down on the boiler and obscuring the driver's forward view, already compromised by the size and length of the boilers).

[jim.snowdon]

3 hours ago, The Johnster said:

The Lord Nelson solution is better, but there is a down side; there is an awful lot of exhaust steam and gasses to get rid of on a more continuous basis at a relatively low exhaust velocity, resulting in the very large diameter blast pipes and Lemaitre chimney, and a need for smoke-lifting (mind you, this was a common feature on a lot of 20th century big engines where the smokebox diameter only allowed a very short chimney and smoke and hence the problem of smoke and steam hanging down on the boiler and obscuring the driver's forward view, already compromised by the size and length of the boilers).

The volume of exhaust steam remains the same whether the set for 4 beats per revolution or 8 - what changes is the peak flows. The exhaust pressure is, and should be, low for maximum cylinder efficiency, which in turn means that the blastpipe and chimney, in reality an ejector, has to create the necessary draft with a lower exhaust gas flow. That is where the likes of the LeMaitre and other patented arrangements come into their own.

[kevinlms]

19 hours ago, The Johnster said:

It's cheating to cite Garratts as having more than four cylinders, as they are two engines fed by a common boiler

 

No it isn't cheating - it's a fact that these are 'locomotives'. No one refers to them as '2 engines fed by a common boiler'. Same applies to North American Malletts and other articulated steamers - they were regarded as locomotives.

 

As you are undoubtably aware, most Garratts managed quite well with 4 cylinders. But the LNER one & 3 NZR had 6 each.

[Andy Kirkham]

2 minutes ago, kevinlms said:

No it isn't cheating - it's a fact that these are 'locomotives'. No one refers to them as '2 engines fed by a common boiler'. Same applies to North American Malletts and other articulated steamers - they were regarded as locomotives.

 

I think the point is that there's nothing novel or interesting about fitting each of two engines with three cylinders. On the other hand fitting six cylinders to a single engine requires the designer to completely re-think the mechanical layout of the engine.

 

[kevinlms]

3 minutes ago, Andy Kirkham said:

 

I think the point is that there's nothing novel or interesting about fitting each of two engines with three cylinders. On the other hand fitting six cylinders to a single engine requires the designer to completely re-think the mechanical layout of the engine.

 

But that makes the OP's question, as to whether any locos had more than 4 cylinders, as ridiculous as there is no space on a single chassis.

So I answered the original question. Where did it say that it had to novel, interesting or that 2 chassis fed by a common boiler are eliminated?

 

What about the Kitson steam-diesel loco? Does that meet the criteria as originally asked - I say no, as not merely a steam loco! An entirely different beast.

[Jeremy Cumberland]

1 minute ago, kevinlms said:

But that makes the OP's question, as to whether any locos had more than 4 cylinders, as ridiculous as there is no space on a single chassis.

Paget's experimental locomotive for the Midland Railway (No. 2299, built in 1908) had 8 cylinders, all between the frames and all driving the same six-coupled wheels, so they are undoubtedly all part of the same "engine". It wasn't a success.

 

You could say that eight single-acting uniflow cylinders is merely the same as four conventional steam locomotive cylinders, but Paget's valve gear would presumably have allowed for double-acting cylinders if he had wanted them, and perhaps if he hadn't been interested in uniflow cylinders, he might have had 8 cylinders anyway for better balancing. On the other hand, if he hadn't been interested in uniflow cylinders, then perhaps he might not have adopted rotary valve gear and built his strange locomotive in the first place.

[ciderglider]

1 hour ago, kevinlms said:

But that makes the OP's question, as to whether any locos had more than 4 cylinders, as ridiculous as there is no space on a single chassis.

So I answered the original question. Where did it say that it had to novel, interesting or that 2 chassis fed by a common boiler are eliminated?

 

What about the Kitson steam-diesel loco? Does that meet the criteria as originally asked - I say no, as not merely a steam loco! An entirely different beast.

1 hour ago, kevinlms said:

But that makes the OP's question, as to whether any locos had more than 4 cylinders, as ridiculous as there is no space on a single chassis.

So I answered the original question. Where did it say that it had to novel, interesting or that 2 chassis fed by a common boiler are eliminated?

 

What about the Kitson steam-diesel loco? Does that meet the criteria as originally asked - I say no, as not merely a steam loco! An entirely different beast.

As the OP I apologize for posing the question ambiguously. I should have added the proviso "per set of coupled wheels".

[rodent279]

Oh don't apologise, picking over fine details and arguing the toss over piffling trivialities is a recurring feature of RMWeb!

[Jeremy Cumberland]

 

16 minutes ago, ciderglider said:

I should have added the proviso "per set of coupled wheels".

That excludes divided drive locomotives, where different cylinders drive different axles in a coupled set, which might not have been your intention. They weren't that common in Britain, but some of the examples are important to this discussion, perhaps most notably the Lord Nelsons.

 

Divided drives in large "modern" locomotives I think invariably had the inside cylinder(s) drive the front axle and the outside cylinders drive the second axle, and seem to have been adopted primarily because either the inside cylinder(s) connecting rod or valve gear would have fouled the front axle if the inside cylinder(s) drove the second axle.

[melmerby]

6 minutes ago, Jeremy Cumberland said:

Divided drives in large "modern" locomotives I think invariably had the inside cylinder(s) drive the front axle and the outside cylinders drive the second axle, and seem to have been adopted primarily because either the inside cylinder(s) connecting rod or valve gear would have fouled the front axle if the inside cylinder(s) drove the second axle.

There's at least one class of locos where the first axle is cranked, although the drive is to the second axle, this was done to give clearance for the inside connecting rod(s).

Edited July 12, 2023 by melmerby