WESES Road run

[3816]

Originally Posted by Steam Man

OK, I have a friend who is a retired physics teacher who, hopefully has sorted this issue out.

Steam or water vapour is only invisible below 100C; if a tight fitting damper successfully limits enough air entering the fire box to dampen the fire within it, then the exhaust gasses from the cylinders are emitted into the chimney. This allows the steam exhausted from the cylinders to cool more quickly, thereby reaching the critical (or visible temperature) of 100C when water vapour becomes visible, or precipitates. Conversely, climbing a hill with the damper open greatly increases the mix of firebox gasses mixing with cylinder gases, thereby raising the temperature well above the critical temperature for water vapour to be visible.

So there, its not called primming anymore !!!

Steve.

[Pride of Somerset]

Originally Posted by 3816

So there, its not called primming anymore !!!

Steve.

But surely it is - we are talking about two completely different things here aren't we??

[Charlie D]

Originally Posted by Pride of Somerset

But surely it is - we are talking about two completely different things here aren't we??

Priming is the carry over of water droplets from the boiler to the cylinder with the steam. The main causes are:-

Too much water in the boiler.
Dirty water in the boiler which may foam or have sludge floating on the surface.
A worn piston and or cylinder bore which makes the engine use steam so fast that it pulls a string of water with it.
Rough handling of the engine.

Priming is accompanied by hammering in the cylinder as water cannot be compressed and often results in bent -and -broken bits of engine in severe cases.

'White' steam at the chimney top is a result of low fire temperatures-and therefore low gas temperatures which allow the exhaust steam to condense when the steam reaches the air. Some engines have very airtight ashpans which stifle the fire, and therefore cause white steam, conversely if you have watched the replica steam carriage called Enterprise you never see steam from that as the exhaust is reheated in a heat exchanger in the boiler.

Charlie D