Benefits of Double Chimneys?

[Corbs]

More specifically, what are the benefits of double chimneys/double kylchaps on 2-cylinder locos?

 

I can think of lots of 3 and 4-cylinder locos that had these in the UK but only a handful of 2-cylinder ones, some 9Fs and some of the GWR 'Counties'.

Was there a reason for this? 

Would sticking a double kylchap on something like a WD 2-8-0 have made any difference?

 

Any help appreciated.

[Dunsignalling]

All the Counties got double chimneys in the end, IIRC.

 

I suspect the slower speeds freight locos generally operated at meant the freer flowing exhaust just wasn't required. Indeed, there is one well-known case of a smaller-wheeled type initially provided with double chimneys which appear to have been a distinct disadvantage, and were removed; the Ivatt 4MT Moguls.

 

By contrast, the performance of a batch of BR4 4-6-0s, built new for the Southern Region and so equipped, was reputed to rival that of their larger 5MT cousins, and the WR added double chimneys/blastpipes to a number of theirs. I've always thought it slightly odd that no trials were ever made (AFAIK) using them on either LMS or BR Class 5MT locos, given that 5XP Jubilees did get them. 

 

There may be a parallel with the internal combustion field, where competition-oriented engines achieve higher revolutions, and produce greater maximum horsepower using low-resistance exhaust systems, but at the cost of reduced low-end and mid-range pulling power plus increased fuel consumption. 

 

Just a case of "Horses for Courses"?

 

John

Edited October 4, 2018 by Dunsignalling

[Phil Bullock]

More specifically, what are the benefits of double chimneys/double kylchaps on 2-cylinder locos?

 

I can think of lots of 3 and 4-cylinder locos that had these in the UK but only a handful of 2-cylinder ones, some 9Fs and some of the GWR 'Counties'.

Was there a reason for this? 

Would sticking a double kylchap on something like a WD 2-8-0 have made any difference?

 

Any help appreciated.

 

Increased power output by raising more steam under heavy working conditions was the theoretical name of the game.

 

The LMS thought that sticking double chimneys on Ivatt 4mt 2-6-0s would increase their power output. Biggest disaster ever! They were known as Doodlebugs on the S&D for their erratic steaming and quickly reverted to single chimneys. However the Standard 4mt 4-6-0s on the Southern with double chimneys were reckoned to be equivalent to Class 5s and were worked accordingly on the SW division.

 

So I guess this tells us that any chimney - be it single, double or one of the ejectors - Lemaitre or Giesl - needs to be part of a properly designed gas circuit with adequate air flow through and across the fire bed coupled with correctly proportioned blast pipe nozzle and chimney petticoat. There are plenty of reports of locos with poor arrangements - Manors and Jubilees immediately come to mind - that had to be investigated and modified to cure their steaming issues.

 

The only BR 2 cylinder loco I can think of with an ejector is 9F 92250 but that probably didnt last long enough for any sensible assessment and IIRC the 9Fs were pretty good steamer raisers with a single or double chimney.

 

Phil

Edited October 4, 2018 by Phil Bullock

[DavidB]

....this tells us that any chimney - be it single, double or one of the ejectors - Lemaitre or Giesl - needs to be part of a properly designed gas circuit with adequate air flow...

This even applies in our scales - the Accucraft NGG16 Garratt (OK - it's a 4 cylinder design powered by gas and without the need for the Stephensonian draught to draw a coal fire) was a notoriously poor performer when first introduced and this was traced to a tight spot in the exhaust circuit that was choking the loco. My own model had to be driven very hard on 80psi to haul seven WHR cars around my line and would be winded after two or three laps - after modifications that gave each set of cylinders a separate exhaust circuit, it can now haul the same load with minimal effort on just 45psi for lap after lap.

 

I guess the reason that double chimneys weren't widely applied to 2 cylinder locos was simply the lack of need for the additional power, so the cost/benefit ratio didn't add up. Per discussions on the National Preservation website, the effect of fitting a double chimney to a Castle was to increase available power by up to a third - the highest known power output of a single chimney Castle was around 1,500 dbhp, but double-chimney 5043 sustained 2,000dbhp (equivalent to a strong Class 47) for mile after mile up the Settle and Carlisle a few years ago, as well as demonstrating a considerable capacity for running at high speed on minimal steam. I wonder just how many 2 cylinder locos needed that kind of extra performance on a day-to-day basis. I recall an introduction to the Locomotives Illustrated edition on the 9Fs that referred to the experience of a crew when taking a 9F on a night-time fast fitted freight on the ECML - from memory, the loco's performance was completely different from any 9F they had driven and fired before, but it wasn't until the end of the journey that they were able to see that it was the first of the class to be fitted with a double blast pipe.

 

David

Edited October 4, 2018 by DavidB

[Corbs]

Thanks all for the speedy and informative replies, I think I understand more now. I'd forgotten about the Ivatt 4MT (I was not aware the experiment had failed) and the Std. 4MT. Were any Std. 5MT locos so fitted?

[Poor Old Bruce]

Thanks all for the speedy and informative replies, I think I understand more now. I'd forgotten about the Ivatt 4MT (I was not aware the experiment had failed) and the Std. 4MT. Were any Std. 5MT locos so fitted?

 

No Standard Fives had a double chimney. Ivatt did equip some of his Black Fives but it may have been just the Caprotti ones. The Stephenson valve gear Black Five had a double chimney in BR days.

[DavidB]

The other factor to consider, based on Peter Smith's memoirs about firing double chimney 9Fs over the Mendips, was the sheer human cost of feeding the monstrous appetite for coal when producing 2,000hp from a two cylinder machine. Fine on a day when the fireman was on top form and all conditions were favourable, but too much to ask of someone day in and day out, which would make regular rostering to take the benefit of the extra power simply unrealistic from a human dimension.

 

I've just checked and the introduction to the Locomotives Illustrated edition on the 9Fs mentioned above was written by a RMWeb regular who may have more to say on this subject. Paging Stationmaster Mike, paging Stationmaster Mike.....

[Wickham Green]

The other factor to consider, based on Peter Smith's memoirs about firing double chimney 9Fs over the Mendips, was the sheer human cost of feeding the monstrous appetite for coal when producing 2,000hp from a two cylinder machine. Fine on a day when the fireman was on top form and all conditions were favourable, but too much to ask of someone day in and day out, which would make regular rostering to take the benefit of the extra power simply unrealistic from a human dimension.

 

 

....... hence the trials with automatic stokers ........................ but far too late in the day, of course !

[Dunsignalling]

The other factor to consider, based on Peter Smith's memoirs about firing double chimney 9Fs over the Mendips, was the sheer human cost of feeding the monstrous appetite for coal when producing 2,000hp from a two cylinder machine. Fine on a day when the fireman was on top form and all conditions were favourable, but too much to ask of someone day in and day out, which would make regular rostering to take the benefit of the extra power simply unrealistic from a human dimension.

 

 

True, and perhaps the reason for the ten-coach limit placed on the 9Fs over the S&D, which always seemed low in relation to the known abilities of the loco. Given that the 9Fs, if provided in greater numbers, could have greatly reduced the amount of double heading required on that line, one wonders, in hindsight, if the provision of second firemen might have been a practical economy in place of extra engines.

 

As to the efficacy of the double-chimney 9Fs in general, there doesn't seem to have been a down-side and there were plenty of other lines/duties where having the higher power in reserve would have been useful for short spells without overworking the fireman.

 

John

 

 

 

.

[Phil Bullock]

Yes Saltley had the stoker equipped 9fs which Iirc also had double chimneys. Intended turns were the overnight fitted freights to Carlisle. Given there were only 3.... 93165/6/7... Insufficient effort was put in to providing appropriately graded coal so jams in the feed screws were a recurring issue. Riddles and the 9fs is a good read on the subject.

 

A 10 coach limit on the S@D wasn't always observed...wasn't the last up Pines loaded to 13...and even worse got checked on the climb to Masbury? Oh to have been on that train... Peter Smith and Aubrey Punter put up a great show by all accounts.

[Dunsignalling]

Yes Saltley had the stoker equipped 9fs which Iirc also had double chimneys. Intended turns were the overnight fitted freights to Carlisle. Given there were only 3.... 93165/6/7... Insufficient effort was put in to providing appropriately graded coal so jams in the feed screws were a recurring issue. Riddles and the 9fs is a good read on the subject.

 

A 10 coach limit on the S@D wasn't always observed...wasn't the last up Pines loaded to 13...and even worse got checked on the climb to Masbury? Oh to have been on that train... Peter Smith and Aubrey Punter put up a great show by all accounts.

AIUI a pilot was available for the final up Pines, but the enterprising crew decided to take their last opportunity to see what they, and the loco, could achieve unassisted. 

 

John

[Phil Bullock]

Yes for anyone with an interest in operating the S@D a read of Peter Smith's books is a must....footplate over the mendips and mendips enginemen. Well written and informative.

 

Phil

[bike2steam]

Would sticking a double kylchap on something like a WD 2-8-0 have made any difference?

 

 

I wouldn't've thought it necessary with such 'plodders' which were more than capable enough on slow mineral traffic, and with a tendency to shake themselves to pieces if they worked much over 40mph.

[bike2steam]

By contrast, the performance of a batch of BR4 4-6-0s, built new for the Southern Region and so equipped, was reputed to rival that of their larger 5MT cousins, 

True enough in theory although some crews preferred the 'pocket-rockets'/standard 4 moguls for the more frequent stopping local passenger services such as Waterloo to Basingstoke, because of their better acceleration.

[Corbs]

Got it, so the comparison with the large exhausts on cars seem a good analogy (loss of low end torque but more power higher up, or whatever that equates to in a steam loco).

As I understand it then, a Giesl ejector had different (claimed) benefits and applications to something like a double kylchap?

[PatB]

The other factor to consider, based on Peter Smith's memoirs about firing double chimney 9Fs over the Mendips, was the sheer human cost of feeding the monstrous appetite for coal when producing 2,000hp from a two cylinder machine. Fine on a day when the fireman was on top form and all conditions were favourable, but too much to ask of someone day in and day out, which would make regular rostering to take the benefit of the extra power simply unrealistic from a human dimension.

 

I've just checked and the introduction to the Locomotives Illustrated edition on the 9Fs mentioned above was written by a RMWeb regular who may have more to say on this subject. Paging Stationmaster Mike, paging Stationmaster Mike.....

 

Not just 9Fs of course. Given the rarity of mechanical stokers in the UK, and a general lack of enthusiasm for oil firing, the ultimate limit to British steam locomotive performance has always been how much coal can be shifted by one man (maybe 2 if there's room in the cab) with a shovel on a sustained basis.

[The Johnster]

All of which suggests that double chimneys are not necessarily an advantage in themselves, and the draughting is a dark art practiced in gothic halls lit by black candles by blokes in hooded cloaks to the accompaniment of sinister medieval choral music and obscure but somehow frightening  chanting somewhere in the background.

 

This is not that much of an exaggeration, of course.  A double chimney makes a loco look more modern to my eyes, and even I, who understand little of the practicalities of the situation, can see that big boilers on multi-cylinder loco produce a mahoosive volume of exhaust that has to be got rid of quickly and efficiently or it will hold the loco back.  Double chimneys perceptibly improved the performance of Castles, Kings, Royal Scots, Patriots, and LeMaitres or Giesels did the same for Southern engines,  Even the mighty A4, speed of a greyhound and strength of a boar, was improved with the Kylchap into a world beater.

 

Modern boilers are, by and large, very good at raising large amounts of steam very quickly, so there was, by post war times, a possible use of these sorts of draughting arrangements on less glamorous engines, 4 or 5MTs.  But it was hit and miss; a failure on the Ivatt moguls, not even tried on their BR standard derivates, but a considerable success on the BR standard 4MT 4-6-0 which was an indifferent steamer initially.  Double chimneyed 9Fs were appreciated on the Ebbw Vale iron ore trains, not a high speed effort and much more a pure slog.  

[PatB]

Thing is, unless there is some single choke point in the draughting system, improving any one area probably won't help a great deal as all that will happen is that you'll run into a limitation elsewhere. Engines, whether internal combustion or steam are systems, and any attempt at improvement needs to view them as such, rather than as a collection of individual components. No point adding extra blastpipe/chimney area if the grate's the size of a postage stamp.

[34theletterbetweenB&D]

 The analogy with IC piston engine exhaust is flawed. There is no power loss or torque reduction from something like a Kylchap, Lemaitre or Giesl ejector. It's almost like a magic trick, compared to the simple blastpipe, single or double, these devices which increase the surface area of the exhaust steam in the smokebox deliver better entrainment and thus superior exhaust ejection of the combustion product from less residual enegy in the exhaust steam.

 

The boiler has to be designed to suit. A well known episode in LMS development was the fitting of a double Kylchap ejector to Jubilee 5684. The large free gas area of the tube nest typical of Crewe narrow firebox boilers (for free steaming with a conventional blast pipe arrangement) resulted in lifting of the fire and swiftly filling the smokebox with ash when working hard. Too much of a good thing, and since Crewe didn't want to redesign the boiler to suit the ejector they stayed with the conventional blast arrangement

The other factor to consider, based on Peter Smith's memoirs about firing double chimney 9Fs over the Mendips, was the sheer human cost of feeding the monstrous appetite for coal when producing 2,000hp from a two cylinder machine. Fine on a day when the fireman was on top form and all conditions were favourable, but too much to ask of someone day in and day out, which would make regular rostering to take the benefit of the extra power simply unrealistic from a human dimension...

 As remarked above, given equivalent design quality, the power out of a handfired steam loco is directly proportional to the work rate of the man firing . So how was it that firemen on wide firebox designs with 40 to 50 sq ft grates managed day in day out on the LMS and LNER routes? There were incidents on both A4s and Princess Coronations on up runs when conditions were adverse (headwind, high demand for steam heat) that bunkers of 9 to 10 ton capacity - larger than on any 9F - were emptied well short of London. Better men?

[The Johnster]

Possibly better riding engines; a 3 or 4 cylinder pacific with 6'8" or 6'10" wheels rides better and delivers power more smoothly than a 2 cyl 2-10-0 with 5' wheels.  Poor riding makes the fireman's work much harder; apart from tiring him as he braces himself against it, it makes balancing while you are firing much more of an effort and effects the accuracy of where the round lands in the box.  The only plus side is that, if it's very bad, it'll shake the firebed into an even level for you and shake coal forward in the tender.  

 

One hears stories of WCML and ECML trains running the last 10 miles or so into Euston or KX on coal dust with empty tenders, and of Kings and Castles doing the same into Paddington.  Incredible amounts of physical effort were put in by top link firemen especially if things were not going well; men needed to be physically fit and tough to be able to cope with the daily work load.  The heaviest British work was uncomfortably close to a level that demanded oil or mechanical firing, and aids like coal pushers were employed on the WCML.  The mechanical stoker 9F's at Saltley were used on the overnight Leeds/Carlisle express goods, recognised as the toughest job on the railway at the time and involving 950 ton trains running to 60mph class C timings.  

 

Bigger engines were never needed; UK traffic is limited to passenger trains of about 600 tons and freight of about twice that by the length of loops and layby sidings, and signalling clearances, 20 coaches or 60 10' wheelbase wagons.  There were exceptions to this with special signalling and timetabling arrangements, notably on London bound coal trains which loaded to 90 or 100 wagons on the GN, Midland, LNW, and GW routes, and others locally like the local traffic on the SWML between Severn Tunnel Jc and Cardiff Tidal/Marshalling, relief lines only and allowed 90 wagons.  

 

But increases in speed, such as happened from the 60s onward, would have needed something to have been done had steam been retained.  Oil firing would have been the answer IMHO, and the messy stuff would have hit the fan in '74 like it did for road transport!

Edited October 4, 2018 by The Johnster

[Right Away]

It all comes down to draughting.

 

If a single chimney/blastpipe configuration produced optimum steaming rates and ejection, there would not be a requirement to investigate further. Where locomotives "fell short" of expectations, a double chimney was one of the remedial strategies that were implemented.

 

It was as mentioned above, quite a science to get things right.

[Phil Bullock]

Its important to remember that its not blastpipe area that is key - its the design of the blastpipe and chimney petticoat to create the most appropriate venturi effect to draw the right amount of air at the right speed through the grate to achieve optimum combustion and allow optimum heat transfer under conditions of the heaviest load.

 

As discussed some engines were flawed and crews took things in to their own hands. Another gem from Peter Smith is the use of the Jimmy or Chopper - manufactured in S&D company workshops - which fitted over the blast pipe and reduced its surface area, thereby increasing the velocity of the flow of exhaust steam from the cylinders, increasing the venturi effect in the smoke box and therefore increasing the draw on the fire. It certainly wasnt in the rule book! 

 

And neither was the clip - a device applied to the brake valve on the loco which held in the valve controlling steam to the vacuum ejector IIIRC thereby reducing steam consumption and therefore leaving more available for traction. Highly illegal and failure to remove it before making a brake application mean that the tender brakes were not applied when braking the loco possibly leading to at least one significant run away accident.

 

But going back to consistency of performance and the reproducibility of loco performance the calorific value of the coal provided needs to be considered when thinking about the firemans workload. Its not tonnage he has to shift but the required amount of coal to deliver the required amount of energy once this is taken in to account. And coal can burn too hot - as witnessed by those on the Castle special of May 64 when Pendennis's firebars collapsed due to excessive heat generated by the top quality coal that had been specially supplied for the day.

 

Phil

[brack]

In addition to earlier comments, there is a cost both in manufacturing and fitting and patent fees/licensing. You wouldn't spend money unnecessarily or on a loco where the improvements weren't noticeable.

 

I believe a lot more kylchaps were fitted post WW2 as the patents had expired or the fees significantly reduced. Even so they were concentrated on larger locos working hard at high speeds for long periods of time as this is where the biggest payoff was.

[Gibbo675]

Hi Corbs,

 

Just chucking a chimney on top of a smoke box won't necessarily impact the steaming rate of a boiler in a positive way.

 

The two things that have not been mentioned in any of the above posts are the parameters of the actual valve events, how lead and lap figures affect the functioning of what ever type of ejector is fitted via either exhaust cap or exhaust clearance, and the bit that cannot be designed out of any locomotive irrespective of fuel type or quality, how it is driven and fired.

 

The whole point of the ejector is to draw the fire and pump gas through the boiler, to do this it must use friction to draw the flue gasses through the choke point of the chimney. Form this you may appreciate that the area of steam presented while passing between the blast pipe and through to the choke has to have a ratio relative to the velocity of the steam, the area presented and the volume of gas to be pumped to provide the required steam rate.

 

For example, where a single chimney is employed the steam velocity is high, in a double arrangement on a locomotive of the same type the velocity is reduced slightly and with Kylchap, Lemaitre, Giesel etc the velocity is reduced further. The reduction in velocity is made possible due to the more efficient way that the exhaust steam draws the flue gasses due to the increased area presented between the blast pipe and the choke point. Should the velocity of the steam be reduced then there is less back pressure within the exhaust passages which is a reduction of the locomotive's total internal friction hence the locomotive may be worked more expansively by way of a lower cut off and use less steam for the same amount of draw bar horsepower while retaining steaming rate of the boiler through volume of gas pumped.

 

That the LMS fitted double blast pipes to the 5X's was in my mind a waste of time for their valve liners are grossly undersized for a cylinder with such a swept volume. No matter how much extra friction area is presented in the double ejector arrangement if the steam cannot pass into and out of the cylinder in an efficient fashion then the type chimney is neither here nor there.

 

The steaming rate of a boiler is also effected by the fitting of master mechanics type self cleaning smoke box screens. This was done to 6201 some years back and it was claimed by its support crew that it steamed better than it ever had done before. Strangely though such devices incur a choke point which is a frictional loss to the path of the flue gasses, however this is likely negated by the more even draw of the smoke box vacuum over the tube bank, hence the improved steam rate.

 

As for the Ivatt Flying Pigs I have had quite a bit of mainline firing experience with 76079 which are by way of leading dimensions identical to the single chimney variants and every now and again it would decide not to steam. The cure was to open both dampers, shut the fire hole doors and wind it down the rack to give the fire a good old shake up full regulator, it usually worked. It is my opinion that the locomotive was not being used as intended as they were primarily goods engines designed to work mostly at the 30-50mph range with intermittent bursts of high speed rather then what is effectively express passenger speeds for prolonged periods of time on the modern railway. This would point toward a locomotive with not enough exhaust clearance, single chimney or otherwise.

 

Pip, Pip,

 

Gibbo.

 

Edit; Typos

Edited October 5, 2018 by Gibbo675

[34theletterbetweenB&D]

... and the bit that cannot be designed out of any locomotive irrespective of fuel type or quality, how it is driven and fired...

.

 For a perfect account of this by a time served railwayman of broad experience, Dick Hardy on a Midland driver attempting to drive a Kylchap A4 as he would handle a Black 5, one and a half turns up and the regulator part open, and getting nowhere while nearly killing the fireman. (I think in 'Railways in the Blood' but not in a position to check.)

 

Considerable training - in the UK system by long exposure through footplate grades to build experience - was required to make the different design approaches to steam locomotion work optimally. The French system of formal academic training for both firemen and drivers makes an interesting contrast for any prepared to look at it.