Bulleid rebuilds - Was it for the better?

It's worth quoting DL Bradley at some length on the genesis of the chain driven valve gear:

"Bulleid, like Gresley, did not favour divided drive, and the increased frame length and short connecting rods unavoidable with inside cylinders driving the leading coupled axle. Equally, Bulleid disliked the use of derived motion for inside cylinders, he had seen this at first-hand on the LNER. Standard Walschaerts motion could not be accommodated between the frames if the middle cylinder drove the second coupled axle on account of the leading axle's intervention. Maunsell overcame this difficulty in his three-cylinder 2-6-0s by the introduction of twin eccentrics and a very short combination lever, [NB - this was after they had been rebuilt with three sets of motion from their original configuration with derived drive - Tom] but in traffic, maintenance of this was heavy and the failure rate higher than normal. This left Bulleid with little choice but to evolve an entirely new type of valve motion. Various layouts were investigated at Brighton, including one which employed derived motion direct from the driving axle, but when all proved impracticable Bulleid turned to a separate three-throw crankshaft. This had the advantage of permitting total enclosure of all three sets of valve motion within an oil bath and offered economies of maintenance and preparation. The intention was to drive the crankshaft by means of gears and a propellor shaft, as with the rotary-cam poppet valve motion, but the necessary gears could not be obtained in wartime. A chain drive was substituted in which the crankshaft working the expansion links was driven by two chains, one horizontally from the crank axle to an intermediate sprocket wheel, and the other vertically down to the crankshaft at the bottom of the oil-bath sump, an arrangement which allowed the up-and-down movement of the crank axle on its springs and did not disturb the valve motions." (My emphasis)

Talking about the weight of the motions (and the point about material savings) Bradley notes that the weight of a single set of Bulleid gear was 945lb, against an estimated 1,150lb for a set of Walschaerts motion of size suitable for a Merchant Navy; however, the weight saving was offset by the 330lb of oil in the oil bath. So overall, it had little impact on the overall locomotive weight, though did marginally reduce the unsprung weight. But with regard wartime material savings, it was a shortage of specialist engineering capacity that led to chain drive rather than geared drive, not a notional saving in steel.

Bradley also has the following to say about the reverser:

"Reversing was by steam, not because Bulleid particularly favoured the method, but on account of the wide firebox and triple ashpans not permitting a reasonable arrangement of screw reversing unit. Fine adjustment, unfortunately, was not provided" (!)

Frustratingly, Bradley doesn't elaborate further on why the Eastleigh rather than the Ashford reverser was selected, though interestingly, I was having a conversation during the week with a colleague who is both a driver and a locomotive fitter and is familiar with both designs, and his view was that while the Ashford product is markedly superior in operation, it is also more complex to manufacture. So that may have had something to do with it.

Finally a slight diversion. As well as the Eastleigh reverser, the Bulleids had very limited travel in the motion, and this was accordingly magnified by a rocker with unequal length arms that translated the small motion of the gear into long travel of the valves (but in the process, would also magnify any wear and tear into less precise valve events). Interestingly, both features (Eastleigh reverser and magnifying rocker arms) are shared with the otherwise very conventional Maunsell Q class; when 541 re-enters traffic, it will be interesting to see how precisely it can be linked up, and how that varies with wear and tear.

Tom

 

The design should have had a geared drive as I have stated earlier. However the triple throw eccentric drive would have been another option providing a means was found of eliminating the effect of suspension movement. You can see where Bulleid was coming from. Gresley conjugated gear installations in general left very little for the crews to attend to between the frames. The valve gear for the inside cylinder was accessed by means of doors in front of the smokebox and in the running plate, A4s are a little more awkward and B17s and D49s have the gear to the rear of the cylinders. All you to do is to remember to grease the gear, forget and you pay the price - or rather the lately departed designer does at the hands of some individual named Thompson. Towards the end of steam some very famous locomotives with inside valve gear received the bucket treatment. Bulleid was heading in the right direction sadly at a very bad time. He should probably have learned a little more from his old boss with respect to prototype testing of new designs.
For the average enthusiast the peculiar antics of the originals could been seen as amusing but imagine trying to run a railway with locomotives that could not be depended on to behave in a predictable manner. When some V2s were loaned to the Southern to help to cover for the temporary withdrawal of the Bulleids they were demonstrated working in textbook Gresley/best thermodynamic practice manner, that is full regulator and short cut off. This was not what the crews were used to. It is perhaps a good thing that the V2s were not the very best examples and were not double Kylchap fitted.
If the valve gear had to go there was no good reason not to go further and modify the engines further with modern running plates etc. In truth the engines could have been modified further, Timken, Franklin and all that.
So the rebuilds were for the best but I cannot help but admire 34092.

 

The SAR 25s had cast beds, a number of which we're built by North British. Changing the subject, I always wonder why steam operated fire hole doors were not adopted in the UK (although one can ask the same question re headlights, generators etc), and why they were abandoned on the Bulleid locos. Watching them in action on Chinese locos, it seems such a slick action, and presumably helps reduce blow backs.

 

The same could be said about the Marcotti hand-operated firehole doors on all standard German locos. To see the driver & fireman acting in unison is the epitome of efficiency.

 

hi tom,

the Maunsell 0-6-0 Q had an Ashford steam reverser, and valve gear similar to the 4-4-0 L1 which Holcroft had a hand in designing and by all accounts the valve gear of the L1s was extremely good.

the Southern design team was highly competant at producing efficient valve gears - including novel arrangements such as the Z class inside gear which had an extra eccentric to provide the 'lap and lead' component rather than the usual combination lever and drop link and anchor link. such an arrangement might have suited the MNs and an oil bath, though the gear for the outside cylinders would have had to be on the outside of the loco. Bulleid could even have used the Holcroft conjugated motion if he'd wanted to, or simply copied the Schools class cylinders and valve gear. though that wasnt Bulleid's nature! Bullied's lieutenant Clifford Cocks apparently worked out the chain driven gear arrangement.

cheers,
julian

 

Yes, Commonwealth I believe.

 

Just come across this thread - fascinating stuff. Can I just raise a question about the 'air-smoothed casing? I understood that one of its main purposes was to allow the loco to be cleaned by passing through the carriage washing plants, and that there was even a chimney cover provided on the first few locos (blowback anyone - or were they to be washed dead, towed by a shunter?)

So did this ever happen? Otherwise it's difficult to see a justification, as with the bluff front end there a can have been little aerodynamic benefit?

 

That was the justification; however, I've never seen a photo, and I'm not sure it ever happened in practice, except perhaps for publicity / demonstration purposes. Apart from anything else, the locos weren't shedded where the carriage washing plants were (for example, loco at Nine Elms but carriages stabled at Clapham Junction etc) so in practical terms, even if good in theory, it would have resulted in increased light engine moves near the major stations.

The form was always called "air smoothed" but never, to my knowledge "streamlined". I don't think drag reduction was a consideration (unlike, say, the LNER A4s). On the MNs in particular there was also a huge amount of experimentation with the shape at the front to try to alleviate a problem with drifting smoke, before in the end settling on basically conventional smoke deflectors!

Another interesting operational feature was that - with the MNs at least - the plan was that they were to be kept in steam between duties for extended periods: with water treatment it was something like 8 weeks between washouts. (Can't remember the exact figure as I am away from references). A couple of elderly pre-grouping 4-4-0s were adapted to act as mobile steam generation plant so that pressure was kept constant while the fire was cleaned and (presumably) firebox inspections took place. I don't know how far that scheme went in practice either.

Tom

 

Here's 34081 at the Stewarts Lane carriage washing plant. No info though on if she went through as well.
http://www.34081.brushhouse.co.uk/pics/lge/006.html

 

The aim of the design to go through a washer is mentioned by Sean Day-Lewis but not confirmed. I think there are some practicable considerations which make it unlikely but not imposible.

Firstly cross contamination. Please indulge me whilst I relate a conversation I had with a full time member of C&W. Two black 5s arived at Kidderminster with support coaches which were fiilthy. I said "perhaps they should go through the washer". He replied "they are much too filthy - they would need a hand wash first as the dirt would stick to the brushes and put dirty marks on the next set washed" Given the propensity of the Spam cans to leak oil that could be an issue.

Second consideration the high pressure jets. These go down to solebar level on a coach and are thus in line with the motion. Water in the motion lubricating oil is not good and there must be a risk of dislodging a cork. Also what happens when the jets are in line with the gap between loco and tender. Ever left a window ajar in a car wash?

INMHO I think washing a loco has too many practicable problems

Dave

 

And there was me thinking it was just to make them look nice.

 

I will agree it didnt get on the casing as such, just inside and on the boiler lagging which I believe caught fire from time to time

 

Without the air smothed casing we would not have the nickname Spam Can

 

So what was the solution for the rebuilds? Do they have divided drive?

 

Nor lots of pop rivets to make painting them fun.

 

Never referred to as Spamcans in my circle. They were always Flat-tops.

Happy New Year, BTW.

 

The oil that occasionally caused boiler lagging fires on original Bulleids wasn't from oil bath leaks, those leak onto the track under the loco.
No, the oil contamination of the lagging was caused by oil from the very effective Axlebox oil feed system (top feed to crowns), runs around the axles and drips into the pockets in the driving wheels.
When the wheels turn, the oil is flung up onto the lagging.

 

As an addendum to that - I seem to recall that initially the source of ignition was thought to be from the ashpan. However, careful analysis showed it was sparks thrown up from the brake blocks; a change in the type of metal used solved the problem.

Tom