Yet another exhaust question

[rodent279]

All these questions are exhausting......!!!  (see what I did there? Clever eh?)

 

Been watching a few videos of German steam. Most UK locos with 2/4 cyls have 4 beats per wheel rev. Looking at some 01 footage, it seems to be more, 8 I suspect. This seems to be the case with a number of other types-41, 52, 38, Bavarian S3/6.

 

Was it normal practice on the Continent to have 8 exhaust beats per rev? Is this to even out the drawbar pull?

[LMS2968]

Two cylinder engines have four beats per revolution; three cylinder engines have six. Generally, four cylinder types also have four beats as the cranks on the same side are at 180 degrees so two cylinders exhaust at the same time. On some though the cranks are set at 135 degrees, giving eight beats per revolution, although I'm not sure if this includes the locos mentioned. Many videos are made from old film digitised, and these were silent. The sound is added at the video or DVD stage and from a different source, and isn't always synchronised with the actual film footage.

[Titan]

 Is this to even out the drawbar pull?

 

It is one of the reasons, means the loco can develop a higher average tractive effort without slipping. The other is more even daughting of the fire, you can have more average airflow through the fire without lifting it up through the chimney. The downside is that the valvegear will be more complicated, presumably four sets rather than two, unless there is some way of conjugating it like Gresley did on the three cylinder locos.

[rodent279]

 Many videos are made from old film digitised, and these were silent. The sound is added at the video or DVD stage and from a different source, and isn't always synchronised with the actual film footage.

 

I've actually been looking at recent YouTube footage.

[Nimbus]

It is one of the reasons, means the loco can develop a higher average tractive effort without slipping. The other is more even daughting of the fire, you can have more average airflow through the fire without lifting it up through the chimney. 

 

It must also have helped to reduce the back-pressure in the cylinders, not having to be competing in pairs to exhaust through the blastpipe.

Hence LNER and Southern Pacifics being so fleet of foot?

 

The Nim.

[62613]

It is one of the reasons, means the loco can develop a higher average tractive effort without slipping. The other is more even daughting of the fire, you can have more average airflow through the fire without lifting it up through the chimney. The downside is that the valvegear will be more complicated, presumably four sets rather than two, unless there is some way of conjugating it like Gresley did on the three cylinder locos.

I don't understand the first part of your comment: surely tractive effort is a theoretical figure, based on cylinder dimensions and boiler pressure, and inversely to driving wheel diameter, so the exhaust has nothing to do with that. What a correctly designed exhaust should do is enhance the free flow of steam from the cylinders, and allow the fire to "draw" properly, thus making for a freer-running locomotive. Sadly, even into the later stages of steam loco design, it could be got wrong. 

[LMS2968]

No, Tractive Effort is the force that the engine exerts on the rails to move itself and its train in a particular direction. It is measurable in a testing station such as Swindon or Rugby; on the road it is measured by a dynamometer car, but at the drawbar. A steam loco puts out its maximum tractive effort when stationary and starting its train; the TE then declines exponentially as speed rises until the point is reached where the TE is just sufficient to maintain the speed at that point and won't rise any further. The rate of decline of the TE varies with the engine class and is more rapid with a small wheeled goods engine than a large wheeled passenger one, but there are several other factors as well as wheel diameter.

 

You are talking about Nominal Tractive Effort, a purely theoretical value and useable really only to compare one class of loco with another. Unfortunately, people believe, incorrectly, that it is a measure of power output, and we get ridiculous claims such as the P2 people saying they are building Britain's most powerful locomotive, based entirely on this figure.

[Pacific231G]

Titan, on 27 Dec 2018 - 12:27, said:

It is one of the reasons, means the loco can develop a higher average tractive effort without slipping. The other is more even daughting of the fire, you can have more average airflow through the fire without lifting it up through the chimney. The downside is that the valvegear will be more complicated, presumably four sets rather than two, unless there is some way of conjugating it like Gresley did on the three cylinder locos.

 

I don't understand the first part of your comment: surely tractive effort is a theoretical figure, based on cylinder dimensions and boiler pressure, and inversely to driving wheel diameter, so the exhaust has nothing to do with that. What a correctly designed exhaust should do is enhance the free flow of steam from the cylinders, and allow the fire to "draw" properly, thus making for a freer-running locomotive. Sadly, even into the later stages of steam loco design, it could be got wrong. 

Surely the key words here are "....without slipping". With a more even distribution of the effort through each wheel rotation, the force exerted through the driving wheels would be more constant so, for the same tractive effort, is less likely to reach the point where slipping is likely. That would enable the tractive effort to be somewhat greater before the "slipping point" (I don't know what the technical term for that would be) is reached.

 

Does this relate in any way to the propensity of Bulleid Pacifics to slip?  It was notable at Oxford (where I did most of my steam sniffing as a youngster) that with the same weight of trains the Castles rarely slipped whereas on damp days the Bulleids seemed incapable of starting a train without some slipping- (has anyone figured out how to reproduce that in a model?)  though their drivers were adept at keeping that under control.

Edited December 28, 2018 by Pacific231G

[LMS2968]

The technical term is 'limit of adhesion', but I'm afraid you have somewhat demolished your own argument. The Bulleids were three cylinder engines with six beats per revolution; the Castles four cylinder with only four beats per revolution. However, a 4-6-0 was invariably more sure footed than a Pacific.

Edited December 28, 2018 by LMS2968

[GeoffAlan]

The original Spam-cans had an oil bath for the valve gear. They leaked, just like most motorcycles of the era. I suspect quite a lot of slipping was due to this.

[Pacific231G]

All these questions are exhausting......!!!  (see what I did there? Clever eh?)

 

Been watching a few videos of German steam. Most UK locos with 2/4 cyls have 4 beats per wheel rev. Looking at some 01 footage, it seems to be more, 8 I suspect. This seems to be the case with a number of other types-41, 52, 38, Bavarian S3/6.

 

Was it normal practice on the Continent to have 8 exhaust beats per rev? Is this to even out the drawbar pull?

Were these compounded or simple four cylinder locos?

I've just been looking at videos of three preserved French compounds (231K8, 231G558, and 241P8) and I'm not sure I'm ever hearing more than four beats per revolution but I'll try putting them into an editing programme where I can get an audio waveform.

 

I don't think you can really talk about  a "normal practice" common across continental Europe but not to Britain. Though we tend to think of Britain and "the Continent" as two different places, in reality (apart from the effects of our reduced loading gauge), there was probably as much interchange of ideas between British and Belgian, French or  German ralway engineers  as there was between them.  German practice probably diverged more from original British practice than did French (where, for example, bullhead track was very widely used) but Alfred Belpaire and Egide Walschaerts were both Belgian, the GWR bought from France at least one de Glehn compound for trials, and a surprisingly large number of locos used on France's railways were built in Britain, notably in Glasgow ,including the last SNCF steam locos in commercial service. But, as well as the well known 140C Consolidations, there had been clones of the Highland Railway Castles and a number of the  PO ten wheelers that became class 4-230G. However AFAIK none of these were compounds

 

Compounding was probably more popular in France than anywhere else in Europe, almost to the end of steam, but whether it really did produce the claimed savings of coal is far from certain. I believe that compounding needs long runs at fairly constant speed to achieve maximum savings (so is very effective for stationary engines or for ships with their triple expansion engines going full ahead at constant revolutions for days or even weeks at a time) Long steady runs were to be found in France but it required a high level of technical expertise and knowledge to use the compounding to take advantage of it. 

Edited December 30, 2018 by Pacific231G

[Pacific231G]

The technical term is 'limit of adhesion', but I'm afraid you have somewhat demolished your own argument. The Bulleids were three cylinder engines with six beats per revolution; the Castles four cylinder with only four beats per revolution. However, a 4-6-0 was invariably more sure footed than a Pacific.

It wasn't an argument, it was a question. I've long wondered why the the Bulleid Pacifics were apparently so prone to slipping. Were the LNER and LMS Pacifics - that I saw very little of- just as guilty of this? 

Delving into this a bit further produced various preferred explanations similar to those that my schoolfriends would quote with almost biblical certaintly in the early 1960s. These included; the lower torque from one out of three cylinders rather than one of two or two of four, causing drivers to have to open the throttle further for starting; a certain vagueness in the chain drive's timing (and of course the oil leaking from it) or simply the superiority of Great Western regulators.  

[LMS2968]

All Pacifics are prone to slipping, due to a high power output but restricted adhesion to pass it into the rails. The LMS engines were just as prone, and Gresley restricted the cut-off of his Pacifics to 65% in an attempt to prevent the overload. As far as I know, the rebuilt Bulleids were little if any batter than they had been previously.

 

Although on any engine one (two for four cylinder types) will be putting out more effort than its fellows at any point in time, the other(s), especially on a three cylinder type will also be contributing to the effort. You don't have one cylinder working, which then stops and another takes over. Each is producing a rising and falling output and there is always some overlap between them, especially so at long cut-offs, such as when starting. So while the total power output per revolution is rising and falling, the amplitude is not as great as might be thought.

[Gibbo675]

The original Spam-cans had an oil bath for the valve gear. They leaked, just like most motorcycles of the era. I suspect quite a lot of slipping was due to this.

 

 

It wasn't an argument, it was a question. I've long wondered why the the Bulleid Pacifics were apparently so prone to slipping. Were the LNER and LMS Pacifics - that I saw very little of- just as guilty of this? 

Delving into this a bit further produced various preferred explanations similar to those that my schoolfriends would quote with almost biblical certaintly in the early 1960s. These included; the lower torque from one out of three cylinders rather than one of two or two of four, causing drivers to have to open the throttle further for starting; a certain vagueness in the chain drive's timing (and of course the oil leaking from it) or simply the superiority of Great Western regulators.  

Hi Chaps,

 

I worked with 34067 Tangmere for quite some years while at Riley & Son's, very often driving it, and I have to say that it was not a particularly slippery locomotive.

 

The oils bath leaks didn't cause oil to get onto the wheels, any oil on the wheels came from either the axles or the crank pins in much the same amount than any other locomotive, but mostly dropped within the four-foot and not onto the rails.

 

The main points to heed with the original Bullieds, and not the de-tuned ones that BR made a mess of, are:

• Occasionally some drivers incorrectly used the reversing gear causing slips.
• The steam circuit is very large and so when a slip starts even if the regulator is shut it will keep going until all of the steam is used up.
• The locomotives are designed for fast running with short stroke engines and therefore require a much higher steam chest pressure to get any particular load moving due to mechanical advantage factors.
• The locomotives are three cylinder so only one cylinder will have full mechanical advantage at once, just like an LNER pacific and unlike the GWR and LMS four cylinder locomotives.

There was forty gallons of oil in the oil bath which equates to a massive four inches deep in the bottom when stationary, this reduces when in motion, also the greatest source of leakage from the bath is from oil mist passing through the vents and into atmosphere (otherwise known as the lagging !).

 

As for the lag in the valve events, when in worn condition this is comparable to the Gresley conjugate gear when also in worn condition, when new considerably better than the above mentioned.

 

Do ask if there is anything you more you wish to know.

 

Gibbo.

[rodent279]

All good stuff gents, thanks.

 

I guess a 4-6-2 will be more prone to slipping than a 4-6-0 or 4-8-0 because of weight transfer-the loco will tend to sit down on it's rear wheels as it starts. In a Pacific this means weight shifts from the drivers onto the pony truck, meaning there is less available for adhesion.

 

I asked the question because having seen YouTube footage of various German locos, class 01/38/52 in particular, they seem to have more beats per wheel rev and to accelerate quicker. They also seem very surefooted.

 

I was wondering whether spreading the power strokes more evenly around the wheel revolution leads to a more even distribution of torque, hence a reduced tendency to slip, and possibly quicker starts?

[Pacific231G]

All these questions are exhausting......!!!  (see what I did there? Clever eh?)

 

Been watching a few videos of German steam. Most UK locos with 2/4 cyls have 4 beats per wheel rev. Looking at some 01 footage, it seems to be more, 8 I suspect. This seems to be the case with a number of other types-41, 52, 38, Bavarian S3/6.

 

Was it normal practice on the Continent to have 8 exhaust beats per rev? Is this to even out the drawbar pull?

I've now examined various clips of three preserved French four cylinder compounds (ex Nord 231K, ex Etat 231G and SNCF "standard" 241P) in a video editor with the audio waveform and, though I can't be absolutely certain, they do all appear to have four beats per revolution, the same as a two cylinder simple locomotive. That doesn't mean that other distributions weren't used but I've not come across any.

[The Johnster]

My first acquaintance with Pacifics was the Britannias at Canton in the 1950s, my childhood.  These paralleled the comparison with Castles and Bullieds at Oxford; leaving Cardiff General (as it was called then) in the up direction involves a left hand curve and a short rise to cross the Canal Bridge before the main line drops away to pass under the Cardiff Extension Joint (Valley Lines) east of the station.  Britannias would make as much of a fuss as possible of getting trains moving over this rise, and often take several minutes for the tail lamp to clear the platform (trains could load up to 14 bogies), but would get under way properly once more than half of the load was over the rise and on the falling gradient the other side.  Most drivers favoured having the engine blowing off at the safety valves during this performance, with significant lumps of the fire being propelled with some force out of the chimney, and this added to the general noise levels...

 

Castles, and the Kings when they replaced the Britannias briefly in the early 60s, just accelerated steadily away without any fuss or slipping even on wet greasy rails, as did the Hall which took out the last steam hauled up London I ever saw having taken over from a failed Brush/Sulzer type 4 (class 47) in the September of 1964.  

 

In the down direction, the exit is easier, a right hand curve but the line drops away towards Canton sidings and shed.  Brits working here were often high mileage locos with worn, and hence smaller diameter, driving wheel tyres, with the advantage of greater T.E., so much less in the way of fireworks and drama ensued.  

[jim.snowdon]

Smaller wheels, and we are only talking about a difference of around 2" in 72", will result in a marginally higher tractive effort, and a higher TE for the same adhesive weight will result in a greater risk of wheelslip. The bigger problem is that for a Pacific with uncompensated suspension, as was the case for all of the British examples, the effect of drawbar pull is to transfer some of the weight from the leading driving wheels to the rear and to the trailing truck. The same will happen on a 4-6-0, but the difference is that none of it is lost to a non-driving wheelset. The other significant defect with non-equalised suspension on a Pacific is that it makes them more susceptible to wheel unloading, and thus wheelslip if there is any localised dip in the track. The interesting comparison would be between a Brittannia (or any other British Pacific) and the Pennsylvania RR K4, which was Gresley's inspiration for the GN pacifics, and which, like most US locomotives, did have fully equalised suspension.

 

In terms of the layout at Cardiff, any start that is uphill and on a curve is going to be tricky, due to the changes in the rolling resistance of the train as it enters and exits the curve.

 

Jim

[The Johnster]

Newport is another tricky one in the up direction with a curve and short gradient off the platform on to the river bridge, but the locos had warmed up a bit on the run from Cardiff and less of the fire tended to end up in orbit.  Canton drivers I spoke to in the 70s when I worked at the shed as a freight guard reckoned that the 'high mileage' locos used on the down trains from Cardiff (the best clean new ones were kept for the Paddingtons) were about 'half a coach stronger' because of the worn tyres, and it was appreciated on the banks.  There's a few tricky spots down there; you don't have much of a run at Stormy from a standing start at Bridgend and Neath, tight curve and straight on to Skewen bank.  Swansea High Street is up the hill straight off the platform as well.

 

Canton's Brits were well liked by their crews; if a GW man says an engine is 'nearly as good as a Castle' this is praise of a very high order!   They were worked hard on heavy trains, so any major problems would have soon come to light.  Easier to prep than a Castle, smooth riding, free steaming; there was a lot to like about them!  

[LMS2968]

The Canton men's opinion wasn't generally shared among other GWR crews, though. And it's the first time I've heard a Brit described as smooth riding, especially if compared with a Castle! And that view was shared by LMS men.

[The Johnster]

Well, even the Canton men didn't think they were perfect; the cab was draughty and dust got about everywhere, and everyone agreed they bounced around at speed, but the South Wales trains were more about uphill slogging than fast running and this was perhaps less of an issue at Canton than elsewhere.  They were seriously disliked elsewhere on the WR, particularly Laira, and the region's allocation all ended up at Canton eventually.  The loco the men really wanted for those 14 coach South Wales slogging jobs was the King, and they got them for a brief period to replace the Brits in the early 60s, the LMR taking the Brits.  The story goes that, anticipating resistance from ex GWR men, Marylebone chose names of broad gauge locos for the WR's batch, which started with 70014 Iron Duke, originally allocated to Old Oak.  The Southern was having problems with the Bullieds at this time and were looking to borrow locos; Old Oak saw their chance and sent it to Stewart's Lane as the spare Golden Arrow loco.  A loco named for one originally named for the Duke of Wellington may not have been the most tactful choice for French cross-channel traffic...

 

It is my opinion, and no more than that, that a powerful loco with driving wheels of around the 6'2"/6'3" mark was a better machine for heavy but not especially fast South Wales trains than one with larger diameter driving wheels; the Hawksworth counties did well at Canton as well.  The 'received wisdom' on the WR was that 4-6-0s suited the region's needs best, and that perfection had been achieved with this in the form of a Castle, the later versions of which with better superheaters and double chimneys were very good indeed, but this ignored the demand for lower prep times that was such a feature of the early BR period, and the South Wales sheds' needs were arguably different anyway.  Pacifics were held to be unsuitable for the South Devon banks, and by extension the SWML ones as well, but the Brits were pretty good climbers once they'd got away from the platforms.  Nobody complained about the steaming, even at Laira AFAIK, though some firemen were scared of the big box.

[LMS2968]

Nothing there that I would disagree with! My opinions come down from LMS men, who generally were not fond of the Brits, but even they would agree about their steaming capacity.

[The Stationmaster]

The Canton men's opinion wasn't generally shared among other GWR crews, though. And it's the first time I've heard a Brit described as smooth riding, especially if compared with a Castle! And that view was shared by LMS men.

 

The Canton men didn't get any choice in the matter.  They were lumbered with the Brits whether they liked them or not when the District Motive Power Supt at Newport snapped up the entire WR fleet at a DMPS conference where his colleagues were loudly bemoaning them.  Net result was that some Canton men liked them no more than colleagues at other WR sheds - the cabs were draughty and dusty, they had to be driven from the 'wrong' side and, more importantly, for many Firemen they needed to be fired left handed which did not come easily and if fired right handed overalls could, and did, get caught on the blower valve.  Firing wasn't as bad as a'King' because the Brit firebox was shorter so no need to get the coal so far to reach the front corners but like the 9Fs there was the problem of reaching the back corners although several Old Oak and Canton men I knew well who had fired on them didn't regard them as a problem.

 

And of course they didn't need a gradient to slip on starting - I can well remember them sometimes trying to get away on the Down Main at Reading which was as near level as made no difference (actually 1 in 1300+ falling!) with slipping that made the average Bulleid pacific look like an amateur at the game.  They were pacifics and - AFAIK - they didn't have any compensation arrangement hence adhesive weight transferred onto the trailing truck at just the wrong moment.  By the time the Brits arrived on the Western their can't have been all that many enginemen around who still had experience of working on tender engines with trailing carrying wheels, especially at Canton.

[The Johnster]

On the GW you're looking at anyone who'd worked on Great Bear or the pacifics from the 1925 or 48 exchanges.  So probably nobody in South Wales, then...

 

Great Bear would have been familiar at Old Oak and Bath Road, and the exchange pacifics at Old Oak and Laira; the sheds that hated the Brits the most.  By the way, describing the locos as Brits to Canton men would have result in a blank uncomprehending stare (I can remember Canton men who gave this reaction to everything, mind); they called the locos 70 thousands in the GW tradition of 49s, 28s, 56s and so on.

 

Another factor in their acceptance at Canton may have been the famous GW haycock firing method, which was a sure method of having to stop for a blow up with one of these engines.  But Canton had never used the haycock method as it did not suit the slogging nature of most of the South Wales work, so perhaps Canton and Landore (they crewed the engines as well) firemen were more adaptive to what the Brits needed than men from other parts of the GW/WR.  This is conjecture on my part, but possible.  Certainly some firemen were frightened of the big firebox and found difficulty in getting a firebed in the front corners.  I was told that this was often the bigger lads, whose tall frames hindered them from bending down to the fire hole as easily; the best firemen at Canton for this sort of work were considered to be the small wiry tough guys, who were more agile.

 

Firing the up Red Dragon, 14 on and no respite after Newport, uphill from the bottom of the Severn Tunnel to Badminton with no let up after as you had to run fast to make up what you'd lost on the climb, 5 and a half tons on a footplate that was draughty, dusty, and very uncomfortable on the final run fast run down the Thames Valley, was considered a very tough job for the fireman and most drivers were willing to lend a hand if thing were getting desperate without teasing the fireman about it publicly afterwards, not all were this considerate or sensitive!  But good drivers knew that they needed to work as a team with their mates.  The return working was a stopper, and the fireman usually sat in the driver's seat while the driver 'kept his hand in'.  

 

Nipping out for a pint at Ranalegh Bridge to replace the sweat you'd lost the way up was called 'taking a salt tablet', a term which I believe originated with the 6th Army in North Africa.  Another criticism of the Brits was that they needed a ton more of coal to take a 14 coach train to Paddington for no reason obvious to the firemen except that a loco, and a firebox, that size, wasn't needed when Castles were available.  But Castles weren't available; the WR Brits were to replace Stars that were being previously replaced with Castles.

Edited December 31, 2018 by The Johnster

[roythebus]

To go back to the OP question, remember that videos shot from the air will nearly always have the sound added from another source, otherwise all you'd hear would be the drone of the helicopter engine!

 

Having recently seen a clip fro an early (1948) BBC transport film. that shows a loco pulling away from Liverpool Street, clearly slipping, yet the exhaust is a very steady sound with no sign of slipping!