[locojoe]

Originally Posted by crockhamtown

I can only say that when visiting the Engine House of the Severn Valley Railway I happened to mention the sound a steam engine makes when at a standstill, and someone said that it was the Clack Valve. Heads nodded at this explanation.

Whatever the cause, the sound is so evocative of railway steam engines that I would very much like to obtain a cd of this if there is one to purchase.
~~
Keith

Hello Keith To start we are talking about The Severn Valley Railway and I'll have to admit to having limited knowledge of Great Western engines. I worked on the LNER as a fireman and I'm a bit confused by what you mean when you say a Railway Steam Engine is ticking over.
The LNER engines as I remember did not tick over and clack valves were silent. A clack valve is part of the injector which could on occasion get stuck in the open position by scale from the boiler. This would allow steam through the overflow pipe making a hissing sound.
On some LNER engines as John G has said a Westinghouse steam air compressor or donkey as we called it would make a huffing and puffing while the engine is stationary. Perhaps we need someone who's clued up about GW engines to explain the ticking over sound you heard.