Steam loco's in the cold weather

I would be interested if a member of any footplate crew on some heritage line or other (or the main line for that matter, I don't mind) could explain a technical detail to the not-so-technically-minded like me:-

I have noticed that when it's very cold it seems quite common for steam engines to be emitting a fair bit of steam from the cylinders. At first, when I saw it I assumed the engine in question had a steam leak of some sort. However, having observed it several times, always accompanied by a hissing sound and seen pictures of the same phenomenon in the railway press from various different engines in different locations, I can only guess that in some situations when the weather is cold, the cylinder cocks are kept open rather than closed before or soon after leaving a station.

Is my assumption correct, and if so, what is the reason for this? I would be most interested to know.

Thanks,

John

 

Are you sure it's from the cylinders, sounds like the steam heat to be honest. In any case cold weather makes any leaking glands etc show up really badly.

 

Cold air has much less capacity to absorb moisture than warm air. Hence in cold weather you get a much more visible exhaust, and also any other steam emissions, leaks etc. So you might be seeing the cocks open, or possibly glands blowing etc. The former being below and to the front of the cylinders, the latter to the rear and central. You can't confuse the two.

 

Bear in mind also that cylinders will start colder and take longer to warm through in use, and will lose heat faster when the engine is stopped. The prudent driver will probably keep the taps open longer to ensure that condensation doesn't build up therein.

 

Thanks everyone for enlightening me.