P2 streamlined chimneys

[Atlantic 3279]

My Isinglass drawing 4/385 (for 2002 as built and 2001 as rebuilt with Bugatti nose) including an enlarged detail diagram of the streamlined P2 double chimney shows no "pepperpot" holes on the top of the casing behind the two main pots. As these were a feature of the A4 chimneys I am wondering whether the drawing is correct. I've re-read the relevant sections in RCTS 6B without becoming enlightened on this point in the process. None of the photographs I've checked so far give a view of the top of the chimney of a Bugatti nosed P2.

Does anybody know whether the A4 style pepperpot holes were there on the P2 chimneys too please? I must admit that I don't have the Isinglass drawing for Nos 2003-6.

[2512silverfox]

Graeme

Could it be something to do with the repositioning of the anti vac valves (or snifters as some put it)?

Nick

[S.A.C. Martin]

Email sent, may be of interest.

[Atlantic 3279]

Thanks to you both. I'm not sure where the anti vacuum valves were on the Bugatti-nosed P2s and through which external orifice they drew in air. The removable plates in the streamlined casings, corresponding to the original positions of the valves on the end s/h covers on 2001/2 as built, appear to have no facility for allowing in air.

I've now put this question to the P2SLC too in case their information covers the point.

[61962]

The streamlined P2s were similar to the A4s with the snifting valve behind the chimney. Air was drawn in through the louvres in the side of the casing. The A4 chimney casings were originally made from steel and because the snifting valve discharged steam before closing and to some extent whilst the loco was drifting, the resulting condensation inside the casing caused rapid corrosion and it was necessary to provide an internal cowling around the valve which had a drain pipe running down the side of the smoke box. As the cowling reached the underside of the chimney casing the provision of the pepper pot holes was necessary to vent the valve. At the same time the chimney casing material was changed to copper thus resolving the corrosion issue. Reference to the green book part 2A indicates this change was made with the first double chimney engine "4468" in 1938 with the rest of the class following. As the "streamlined" P2s had been in service for about two years at that time I think it would be reasonable to assume that their chimney casings were similar to the A4s - photographs show the louvres in the side of the chimney, and they presumably suffered the same issue with condensation. It is therefore very likely they would have been altered like the A4s at some time during or after 1938.

Eddie

[Atlantic 3279]

Now that's what I call a useful reply. Thank you for imparting that piece of knowledge.

[AdamOrmorod4468]

Woah, it's weird seeing the A4s without those holes in the chimney. You can see them (or the lack of them) clearly in this video clip: https://www.youtube.com/watch?v=_gPH_rb ... Q&index=13

[65447]

Spencer's paper to the Inst. Loco. E given during 1947 makes reference to this in the text and includes 'before' and 'after' drawings of the exhaust arrangements for engine no. 2004. The images are too large to post here but if Atlantic would care to pm me with his e-mail address I will send the relevant material.

In summary the original chimney for 2004 at least had louvres on the sides but these were replaced by a single circular aperture smaller in diameter than and behind the twin blast pipe orifices.

[AdamOrmorod4468]

How soon did the existing A4s get the redesigned chimney? Would they all have got it by mid 1938 (my proposed modelling period) or did it take a lot longer than that?