The Armistice Kentish Belle 11/11/23

Lovely post.
Small point, but an optimised exhaust arrangement ( and presumably Bahamas is closer to this) would tend to reduce cylinder back pressure for a desired smokebox vacuum in which case the cylinder output/efficiency, all else being equal, has the potential to be higher.

 

Thanks for your kind remark.

You are correct on all counts. The test results (for a steaming rate of 25,000lbs/hr) gave a smoke box vacuum of 5.7 inches of water for the modified SC and 6.7 for the DC. Blast pipe pressures were 8.0lbs/sq in (SC) and 5.5 (DC). It was concluded that theoretically, as a result of the reduced back pressure, there should have been higher power available from the DC arrangement but any differences lay within the limits of experimental error. The steam temperature for the DC was 595F and the SC 625F. It was further concluded that the lower degree of superheat (DC) would also have been a factor that limited/negated the theoretical gain. It was thought that the DC rear barrel being nearer to the tubeplate affected the gas flow in the smokebox. Who would be a boiler designer?

 

Someone a lot cleverer than me...

 

My thanks to @Johnb & @pete12000 for recommending the book. Although a slim volume it contains plenty of great information and photographs as it traces Bahamas from build to the recent overhaul and the second of its mainline return runs in 2019. Inexpensive (£8) and exceptional value.

I now understand the story behind Bahamas’ double chimney; not a “re-use” of the chimney that was used for the Rugby tests, but a new chimney fitted in 1961 to a Derby design and subsequently replaced during the recent overhaul. A copy of the design drawing is reproduced in the book, and it appears to be identical to the double chimney tested at Rugby (as described by Cox).

[In the 1950s the Scots were fitted with self-cleaning smokebox equipment; this had an adverse effect on the steaming. Tests were conducted at Rugby and an identical chimney to that fitted to Bahamas was trialed (albeit with a slightly different blastpipe). The arrangement improved the maximum steaming rate by 5% (20% improvement on a Jubilee compared to the original single chimney). The modification was not adopted, and the self-cleaning plates were gradually discarded.]

 

Do they sell this at Ingrow I wonder...

 

We certainly do, the Society are a registered charity run by volunteers any funds generated go towards keeping our loco's working..

Shop - The Bahamas Locomotive Society (bahamas45596.co.uk)

Thanks for your support!!! We currently have a vac' braked mainline Jubilee and Support coach which give us cause for concern at the moment £!£!!

Pete