Improving loco performance - re-rebuilt Merchant Navy?

corking post - well done. very interesting and not even a mention of paint to boot!

 

Here is what the Derby Drawing Office came up with in 1952 when they started work on the 8P Pacific (from E.S.Cox British Standard Steam Locomotives):-
[attachment=0:2h9mmeh3]Harrison Pacific.jpg[/attachment:2h9mmeh3]
Freddie Harrison was abetted by C.S.Cocks, the Derby Drawing Office manager, who had formerly worked for Bulleid at Brighton. The design envisaged using a boiler with the taper on the under-side like the Bulleid Pacific boiler, to enable the middle cylinder to drive on the internediate axle. No record of the valve gear, though if you look closely what might be conjugated links are shown behind the steam chest??
Unfortunately, or fortunately, depending upon your point of view, it was very swiftly sat on when it arrived at Riddles office at Marylebone!
Would this have been the natural development of the Doncaster/Eastleigh Pacific design?

 

Rumour has it a certain narrow gauge locomotive was temporarily equipped with an in cab sound system and CD player, (just for fun).

 

Worth looking out for, there are also good papers from Gresley, Maunsell, Churchward, Riddles and Bullied over the years.

The most amusing is Gresley's that was published in July 1925 (think - when did Pendennis Castle visit the LNER!):

"A three cylinder locomotive is a cheaper engine to build and maintain than than one with four cylinders and moreover possesses certain characteristics in which it is superior. It will meet the requirements of the near future for increased power, owning to physical limitations, cannot be met by a two cylinder arrangement. Undoubtedly a four cylinder engine can be designed, the power of which will exceed that of a three cylinder locomotive with the same gauge limits, but the construction of such an engine at the present moment would be premature, in the same way that as the construction of three cylinder locomotives 80 years ago was unneccessary for the requirements of the time"

From another source Gresley added after reading this Paper to the IMechE at London: "I understand it is traditional for the speaker now to answer questions from the audience, I however will not be drawn into it. there is such a thing as correspondance!"

 

Well, if you would like to start with Merchant Navy as a subject for conversion here goes.

Remove the rear truck and a portion of the frames then produce a set of extension frames using welded tubular sections and so permit the production of a 4-8-0. This extension would be akin to bar frames and so you could then move on to the next step and remove the wide firebox and replace it witha narrow one. Restore the boiler pressure to 280psi.

Remove the cylinders, because of cost you don't want to produce too many wheel centres, so the only way to improve the tractive effort and so make best use of the increased adhesive weight is to increase the cylinder bore size. Don't worry about the valve size for the inside cylinder just use two piston valves of 6" dia. Make sure your valves are lightweight, multi-ring, fitted with diffusers and lubricated between the rings with unatomised oil. Similar details to apply to the outside cylinders which would be fabricated by welding, ditto the inside block, fitted with pearlitic chromium cast iron liners for both the valve and piston bores. If you can stretch to increasing the superheat temperature then fit cooled valve liners. Piston rod and valve spindle packings to be multi-element metalic.

Exhaust system to be double Lempor since the maths is very much public domain and there is a body of individuals with experience of working with this system.

For the grate it would probably be best to go for a Hulson which would allow the way open for GPCS at a later date - just design your firebox with the secondary air inlets in mind.

Can I spend some more? Please. I would like Franklin wedges, full roller bearings, feed water heater, high levels of thermal insulation ---------.

That's my starter for 10.

Oh, you can fit high power output compounds within the UK loading gauge. Stanier was simply wrong.

 

Yep prepped and fired all day - The heat from a merchant compared to a WC is un-bearable at times......

 

Two fundamentals govern locomotive design above all else.

1) The loading gauge
2) The track gauge

The latter essentially governs the position of the frames and thus the dimensions of the inside cylinders, given that they need to fit beteen them. The outside cylindeers are again governed by the position of the frames and the loading gauge. If you incline cylinders to overcome this, you then impinge on the boiler dimensions.

 

Could the LMS have used a 4400hp locomotive? I would have thought 3600hp would be more realistic. The outside cylinders of a Chapelon rebuilt Pacific were a little over 16.5" bore. The wheels were slightly dished to allow more space for the bearings and the frames set out forward of the outside cylinders to accomodate the 640/650mm nominal 25.5" bore inside cylinder block. There was always the Du Bousquet solution to be tried and the LM engine engine did not need to be so large anyway. The boiler had a maximum diameter of a little under 6ft. on the Chapelon design. Too large for the LMS?

Did Derby try that hard or was it just an exercise in justifying the status quo? Given more recent work on compounding it makes the justification angle look more likely.

 

A few years ago I had a conversation with another enthusiast while waiting for a train at Kinchley Lane. During it, we agreed that a MN with a modern RC valve gear, three cylinder Smith's compounding and re-heating the low pressure steam would be a brilliant performer. A coal pusher would be essential and a very much larger tender generally to house a much larger water supply.

Nice dream!

Regards

 

Lempor exhaust.
Roller bearings
Compensation to coupled wheels and linked to trailing truck as done on most big US locos - minimizes weight transfer. Plus computerized slip control? Converting to a 4-8-0 would be problematic due to the wide firebox.
Third outside Walscherts driving middle cylinder as done on US 4-12-2's (to avoid conjugation and middle eccentric).
Large tender (4/3rds of an existing one )
Mechanical stoker/oil firing if it is really to be used to full capacity for any length of time, otherwise two firemen
Air brakes.

 

Just build a new loco...

 

That requires a few more millions than my speculation envisages. What I'm interested in finding out is, what sort of improvements are achievable on a "normal" overhaul/restoration budget. Heaven knows, £500k is a dauntingly large sum as it is!

Wouldn't driving the inside valves from an outside set of gear be just as problematic as deriving the drive from the outside sets? Besides, I thought the rebuilt Bulleid pacifics have a set of inside Walscherts gear already - or am I getting confused?

Taking the idea of a Lempor exhaust a little further, what would be involved? Obviousy there's some careful design work to do, to replace the multi-jet but single chimney arrangement:
- New exhaust steam passages, at least in part;
- new blast-pipes
- new double-chimney casting
- new petticoat (?)
I guess the chimney is the only thing that needs to be cast - or does it?. The rest can be fabricated, which I expect would be cheaper. What would the expected savings or improvements actually be?

 

An interesting debate, by answering the issues raised by people in the past we can better understand the practical issues surrounding making it work with todays technologies.

I would add that Derby in the 1930s with the Midland heritage and the remanants of Fowlers team (who were ordering compounds in the mid 20s) would probably been more pro-compound minded drawing office than others, nor can Stanier be accused of being predjudiced by his earlier De Glenn compound experiance under Churchward as in the text he admits they suffered because the steam passages between the LP and HPs are too small.
The Coronation Compund's cylinders:
HP - 22.25" outside dia, 17.25" inside dia, 25.6" piston stroke.
LP - 30.25" dia, 25.25" inside dia, 25.6" piston stroke
Between the centre lines of the HPs was 7' 4.2" (the diagram comments that to make the UK loading gauge this had to be 7' with the cylinder castings strengthening webs removed)
Centres of the LPs was 2' 2.75" (a monobloc casting)
Does this match any French locomotives of the period?
There are other issues too (from George Carpenters discussion in "La Locomotive a Vapeur" - A. Chapelon): -
1) Coal was significantly higher in cost in France than the USA, Germany and the UK due to it's shortage of this resource outside the Metz and Alsace regions and the quality was poor being so soft that it was easily lost as unburnt fuel on a hard working simple locomotives, compounds had softer beats - briquettes (compacted coal) being common. Thus there were larger savings to fund the additional designing/building/maintenance costs incurred.
2) Untill 1936 mainline speed was governed by law to 120kph, for pathing and congestion reasons French Express Trains had to be heavier than in other countries. With a maximum axleload of 18.5tonnes compounding was the obvious solution to this.
3) Compound locomotives needed very highly trained drivers to gain any efficiency as a bit more thought was required to the selection of cut-offs. French drivers had more mechanical qualifications than their UK counterparts. They all began as workshop apprentices and becoming a skilled fitter before beginning as drivers at the age of 30 without first becoming a cleaner or a fireman. Firemen were never promoted to drivers and were regarded as unskilled men. A driver would share his engine with only one other driver and would be responsible for specifying all mainteance and would supervise this work undertaken personally (Burt Lancaster as a driver scraping his own bearings and supervising the repairs was quite a acturate representation of a 1940s SNCF driver). According to the display at Mulhouse museum the arrival of the 141Rs ended this tradition. David Wardale in the "Red Book" is very scathing of the skills of many SAR footplate crews realising that the class 26 modifications were effectively useless if the crew were too lazy or unwilling to accept the changes in their driving / firing techniques.
4) French crews were fined for using excessive coal and their bonus system encourage on time arrivals. Compulsory Flaman speed indicators (as fitted to Cock O'the North in France and later most of the LNER A4 fleet) recorded driver behaviour in a similar way to OTMR.
5) SNCF steam locomotives achieved 250,000Km between failures despite being complicated machines. UK locomotives never achieved this despite having simpler locomotive designs. TIA water treatment was standard across France and boiler washouts every 60 days, boilers were in steam for longer periods of time. Were the engineering skills of the big four and BR as good as we would like to think they were?

 

Driving the inside valves from a separate set of outside valve gear avoids the unfortunate multiplying of lost motion and expansion errors in a conjugated drive and allows for easier valve setting while avoiding the inside eccentric which tends not to get oiled etc. If you must have machinery inside the frames you want to keep it to a minmum.

In many ways a 3-cyl engine was ideal for a high power engine in UK conditions providing you could come up with a valve gear setup that didn't cause problems. So I thought it would be worth a try even though there already is an inside gear on an MN which we would discard. An alternative would be Caprotti gear, but then we'd only be copying the Duke and we'd need new cylinders.

 

I understand your logic in wanting to put the middle eccentric outside for ease of access but I'm at a loss as to how this can be done. (Might be helpful if you can point to a piccy of one of these US locos.) It also doesn't do away with the need to go between to oil/inspect the middle big end and the other bits of the valve gear that would have to be there. I'm sure that it is not beyond the wit of man to devise a means of lubricating both the big end and the eccentric from a central lube pump, preferably grease. We did it on some of the big steam mine-winders for the outside big ends. However, you could always go for sealed roller bearings for everything if we are re-designing to that extent.

 

The stroke for the outside hp cylinders 650mm/25.6" the stroke for the inside lp 690mm/27.2", these figures are for the pacifics and the 4-8-0s. Quite modest when you consider that a N & W class J had a 32" stroke on 5' 10" driving wheels and was perfectly good for 100mph+ running.

The LMS appear to have based their design on some peculiar dimensions - or someone within the organisation did. Deliberately? We will never know.

Still, Stanier was the man with whom the buck stopped, so he was still wrong. Wrong then and more so today.

 

Steve,

Look to H220 in Victoria for a locomotive with outside valve gear for an inside cylinder. The Victorian solution is quite neat.

http://www.railwaymuseum.org.au/whattosee_h220.html

http://en.wikipedia.org/wiki/Victorian_Railways_H_class



For all the other bods, if you can have 22 ton axle loads, then the NSW C-38 Class tender might point the way forward. 8,100 gallons of water with 14 tons of coal, on a pair of four wheeled bogies. You might play with the water/coal proportions though, I cannot see that you'd ever need 14 tons of coal in the UK, especially given that 35028 and 46229 have had new tender bodies built with increased water capacity at the expense of coal.

http://www.powerhousemuseum.com/collect ... otives.asp

http://en.wikipedia.org/wiki/3801


Cheers

 

To really come from left field, why have mechanically driven valve gear at all? Heavy, complicated to maintain... With current technology wouldn't something like electronically controlled and hydraulically actuated valves be lighter, cheaper and more efficient? Much less reciprocating weight too.

 

Was Clan Line's tender swapped towards the end of steam? It looks slightly shorter than the larger capacity 6,000 gallon tender given to 35021-35030 as built under British Railways. The higher water capacity to feed the Bulleid boiler is essential if the finished product is expected to run longer journeys than those it was designed for. Mechanically, I suspect the Caprotti arrangement would suit the steaming qualities of the boiler well.

If there was more money coming in as a result of progress on the project, I'm seriously wondering if, for ease of maintenance, it could be possible for the middle cylinder to be removed, another two fabricated, and both placed under the rear of the boiler, achieving a sort of push and pull action on the driving axle, so that one set of cylinders will always be going forward, and the other in reverse? My passive armchair engineer thinking behind this that it would balance out performance in both directions, following the line of thought that resulted in the double Fairlie, except that this would be on the same chassis, rather than on a bogie arrangement.

However, there will be some rather major problems that need to be overcome. Assuming that we are using the frames and chassis of a Merchant Navy locomotive, and the two cylinders are added in the vicinity of the firebox, then a problem will arise in locating a substantial cylinder support bracket in a very difficult area of the locomotive. You would also need to run steam pipes along the side of the boiler to the rear cylinders, which would probably inhibit flow into the cylinders and run the risk of the steam cooling, therefore reducing efficiency and increasing the risk of priming. However, this could be overcome by electrically heating the pipes, and providing modern insulation techniques without getting too complex. You would also need to connect the rear cylinders to the exhaust arrangement, or provide a 'second' blastpipe in a similar fashion to that used on the Caprotti 9Fs. It would then need modifications to the tender to improve ride and visibility, improve baffling of the water tank, and then you have a steam engine that can go equally well in both directions without resorting to the over-complexity of the Leader, especially as just about all lubrication requirements can be accessed from the outside, and that all mechanical elements are outside. However, this would essentially mean that only the boiler would be untouched, and would require rather more than the £500k. I'm probably in the realms of fantasy here, mind you, but its just a thought...