Technical Steam Question

[Sooty655]

Boating on the Caldon Canal today, we passed the Churnet Valley Railway. The passenger service was diesel-hauled, but their TKh49 2944 Hotspur could also be seen across the valley and was in steam. The engine was producing a regular chuff-chuff of steam up the chimney, presumably to draw the fire, but the engine wasn't moving. So my question is..........

How is the regular chuff-chuff (about once per second) produced? I know it can be done using the cylinder exhaust when the engine is moving, but there must be another source for the regularly timed blasts of steam.

[Vulcan Bomber]

On the side of the Smokebox there is a huge, ungainly contraption on 1 side, its a westinghouse air compressor, used for brakes on modern stock (old stuff uses Vacum instead) these work with a piston thats steam driven so the chuff chuff you heard was the exhaust from that which will be used to draw on the fire.

Anything certified for main line use these days has them, they have to but there normally hidden between the frames. 70000 Britannia has hers between the smokebox and smoke Deflectors.


A Batch of 9F's were used to haul the consett Iron Ore trains, the engines carried a pair of these compressors on the Firemans side, they looked rather ungainly. They used them for opening and closing the hopper doors on the Wagons they hauled.

http://www.britishsteam.com/br_std/9F/9 ... -92066.jpg

[Sooty655]

Thanks, VB. That makes sense.

[Vulcan Bomber]

Thanks, VB. That makes sense.

Always happy to get a duster onto an anorak..