Chapelon and related Matters

John Bellwood late of NRMY held the smaller wheeled A2 as best british.
Another source somewhere stated that the fifty square feet grate LNER boilers lost the advantage of better efficiency when working hard to loosing it again waiting for action.
Bigger wheels and grates are not best always.
Mr Witte of DB proposed to blank 20% of grate area of in the 8000 leftover boilers from baureihe 50/52 after WW2 when lignite burning was not longer required.

 

I believe it's to do with weight distribution and balance on lightweight track. The Italians made essentially three designs like that - Gr 625 (as above), Gr 640 (broadly the same but with larger driving wheels) and Gr 745, a 2-8-0. Sadly none of the latter survive, but plenty of the others do.





They even rebuilt 625s with Franco-Crosti boilers and Caprotti valve gear, but still with the inside connecting rods - not the prettiest class!

 

"Look Mr Picasso, we gave you a fair trial in the drawing office, but we really don't think you are cut out for railway work. Perhaps it is time you left our service and spent more time trying to sell the paintings I believe you dabble with in the evenings?"

Tom

 

Given that the French Atlantics had right angle bends in their steam pipes and slide valves for their LP cylinders but were pretty the equal of Churchward's Atlantics, it is surprising, to say the least, that Churchward failed to further investigate compounding.

 

Arguably the weirdest feature of that beast is the extra coupling rod to drive the Caprotti gear.

 

Thank you for that. They say a picture is worth a thousand words and I reckon that applies here, even if my understanding is still incomplete.

 

More an eccentric rod than a coupling rod. The furthest end is attached to a crank. The 623 Class had a Franco-Crosti preheater on both sides.

 

One feature of the GW arrangement is the relatively short link connecting the rocker to the outside valve. As the rocker moves to the back of its stroke the angularity of this link increases, as shown in Don Ashton's diagram but without further mention, thus further reducing the travel of the outside valve. Thus in general terms, the outside valve moves faster than the inside at the front of its stroke because of of the greater length of the outside arm of the rocker, and more slowly at the back of its stroke because of the angularity of this link and also because the rocker is moving away from the direct line.

 

Thank you for posting this. I assume the numbers are the amounts in inches for full travel, although I guess it does not really matter. This is a similar analysis to working out the backset for the expansion link as that is also informed by the fact that as you move away from the "vertical", the "horizontal" displacement reduces for the same angular swing. I wonder why the movement is asymmetric for the inside valve? It could simply be due to the distortion which usually shows up at maximum travel (see below re 44767).

I think Don Ashton did some tremendous work but he could be somewhat cryptic in his writing and his zeal for perfect valve tables while commendable and indeed the logical target for his analytic work, seems to have little relevance to the real world, witness the issues already discussed and the poor indicator diagrams for Gresley gear which did not seem to hamper the locos much. The best valve event tables I have seen are for 44767 (to compare with the King diagram, there is a difference in front and back port openings of 3/16" / 0.1875" at 80% cut-off). There are rumours that Ivatt wanted to show the GWR how to "do" Stephensons but the LMS valve events were otherwise nothing special although the two cylinder locos were usually fairly symmetrical in the normal running cut offs. It took them several attempts to sort out the 3 cylinder 4-6-0s which ended up as not very long lap locos, but with 5/16" lead ensuring they could get plenty of steam into the cylinders.

 

? Imho this would be true if there was no short link on the inside valve rod. Since there is a short link the above argument is also valid for the inside cylinder which has a reverse movement, slowing at one end and a faster movement at the other end of
the rocker seems contradictory.

 

No short link on the inside valves, the inside valve is attached to a tail rod that is driven directly off the radius rod/combination lever, the rocker arm is driven off the tail rod, so no reduction in travel at either end on the inside valves.

 

Yes, correct! On a second look it appeared to be connected with a sliding block!

 

Finally got a copy of Rogers’ Chapelon book. Now starting my read. Lots to do already!