P2 Locomotive Company and related matters

A thought I had - it looked stunning but it was not what even Gresley called a success. Getting someone to build a water tube boiler for it might also be a problem.

 

I think they mean the rebuild version, A4 with a 50sq ft box

 

Generally wish list projects are for the original version and the original W1 would certainly turn heads as well as presenting some technical challenges - 4 cylinder compound, water tube boiler and 450 psi.
If we get started in 2016 and allow 13 years for the production that would have it running just 100 years after the original first ran its trial trip on Dec 12 1929.
Now there's a challenge!

 

No... The original with the water tube boiler

 

When I joined the P2 group I suggested this as the third project and got a two word answer.

 

I guess the second word was " off "

 

Thing that makes me smile/laugh is that the P2 was, for want of a better term. "Beer talk" down at the pub over a pint or two, whilst Tornado was being build and they are now talking of a third machine. The pub talk being one of the following; V4,V1/V3 or K3, if the railway press is to be believed. Pass a pinch of salt please.....

 

Why not meet half way? Outward appearance of the original with conventional boiler and what underneath

 

I don't think a conventional boiler could possibly have the same shape as the original.

 

Correct!

 

That a shame I was hoping for 'yes certainly'

 

The 4 cylinder compound part is easy. Boilers working at more than 450psi are not uncommon but you will not find them on railways. 300psi, there or thereabouts, was a common maximum working pressure to be found elsewhere in world when the Stephenson type boiler was being used. So with the water tube boiler a requirement, you could probably get one designed but getting it built might prove to be another matter.

One area that would need a great deal of attention would be the frames. A conventional locomotive has a degree of stiffening offered to the frames by the boiler but the water tube is unlikely to offer this. The W1 if correctly driven, which according to the surviving test data it never was, would have been the most powerful locomotive in the UK in purely horsepower terms and the frames would need significant redesign in order to withstand the forces placed on them.

But as the A4 could have been a compound if the W1 experiment had offered quicker results. So a Super A4, following the true De Glehn layout (inside low pressure cylinders) would be attractive. The boiler pressure could be 300psi, and because compounds use steam more efficiently there would be no need for a boiler any larger than that originally fitted. You could possibly make it a little smaller. Stir into the mix all the modern piston and valve design details (no need for poppet here), interstage superheater, a modern lubrication system, Frankin wedges, roller bearings, etc. etc. and you would have a very interesting machine to play with.

 

A standard gauge and updated version of this perhaps Mr 242A1..........



Cheers,

Alan

 

What about a Webb Greater Britain 2-2-2-2 just to see if it could be made to work!

 

Since when have boilers provided stiffening to the frames? That would be a recipe for both boiler and frame problems. Anyone who has been on a loco footplate will know that the boiler moves significantly relative to the frames (or, in reality, vice versa.) Boilers are anchored to the frames at the smokebox but generally free at the firebox end, with only support brackets to take the weight as they expand significantly.

 

The time they add stiffness, Steve, is when the loco is being lifted. Considered as a beam, the boiler is considerably stronger than the frames so add vertical strength in those circunstances. But on the road, no.

 

Too true.

 

Well if you are going to achieve anything worthwhile you might as well go for the outstanding.


In the early days of locomotive building boilers were often used as a stressed member (see Fire Queen for a survivor). In more recent times advances in water treatment brought about new thinking with respect to boiler attachment and service life - you might never need to remove a boiler at all. If you fit strain gauges to your boiler and monitor events while the engine is in use you will find cyclic events that are directly linked to the traction and balancing forces occurring whilst the engine is in motion. You may like to also consider the fairly woeful lateral rigidity offered by the traditional plate frame. The plate frame is supposed to offer greater rigidity in the vertical plane but this is insufficient to fully isolate the boiler from traction and motion forces and the all important hornstay integrity is also sometimes lacking. So, is the boiler resisting the external forces applied to it? If the mass and rigidity of the boiler were absent how much more movement would be experienced in the frame structure? If you can say with absolute certainty none then the boiler in no way has any influence on the level of structural integrity offered by the frame construction.

The flexible chassis is very much outdated, undeformable rigidity - all steel cast bed, or fully welded equivalent structure - is the more recently accepted view. All the necessary lateral movement of the wheels should be made possible by mechanisms that ensure the very best behaviour of the locomotive on the track. With such a robust structure offering support the boiler should experience much less of the external stress cycle. Better for the long term health of the pressure vessel? Probably.

I have read it argued that a boiler should never need to be removed from a locomotive during the course of its economic life. This is for a modern design receiving the benefits of T.I.A. or proven equivalent. This has never been tried, hence my use of "might never" earlier. All things being equal I would tend to say that removal would be infrequent but would be speedily accomplished by means of the methods put forward by Col. Cantlie.

 

The issue with boilers though is surely length. A boiler at 225psi is full of water at 200°C if I understood the chart I just found. Expansion of steel, if I understood the numbers I just found for that, means a 4m barrel at 0°C will expand to 4.01m at that temperature. Rigidly attach that to a chassis which stays at 0°C and you are building up all sorts of stresses, so presumably the firebox end must float as it traditionally does or bad things will happen. But equally you must be right it affects the structure. Lengthways its unrestrained and I submit it must be. Vertically, hmm. Probably some effect, and you could engineer bearings to give more. At the moment I think the boiler must have some effect in limiting upwards bend of the frames but not downwards. Not sure its going to be very significant. Need an engineer. But laterally. I think its undeniable that the boiler must be contributing to the lateral stiffness of the locomotive and significantly. Which maybe explains how plate frames can work reasonably well.

 

I have a question I would like to ask about 4 cylinder compounds.

AFAIK The crank angle was always set to 180 degrees for the French compounds and the "Hush-hush", which is obviously a better arrangement for mechanical balance. If we put balance to one side for the moment, I am thinking that these engines may have worked better with the Lord Nelson 45 degree crank angle arrangement. If the HP cylinders have early exhaust release (as for a simple engine), the HP exhaust release would be more likely to coincide with the LP inlet valve being open (with the 45 degree arrangement). I think I may have missed something, because I can't imagine Messieurs de Glehn and Chapelon missing this point.
Does anyone have any thoughts on this?