re priming
 

didnt say i havnt ever primed we were talking about ashpans i will have a look at your ashpan next time i see your engine if you like point you in the right direction.

Thanks for the offer, but as you know, dont let anyone near or up on engine, my ashpan is fine and a direct copy of the one that was in place during its working days, we dont have any problems.

Steve.

Rob, I have always assumed that it is because they - or at least most of them - use superheated steam - but I may be wrong - commentators often are, I'm told!!!!!

I'm keeping out of discussions on priming, but were not the umbrellas to protect the fair ladies against fallout of the cinder rather than nuclear type??!!

Sorry - bit of a daft question but I was just wondering why a tight fitting damper would leave a cloud of white vapour?

If anyone could take the time to explain I would be very grateful

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.

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

Steam is only invisible below 100c as there is no such thing!! Steam below 100c is water vapour - so I take it that you are saying that the gases coming out of your chimney have dropped from above 100c to below 100c halfway up the hill in the video?

Surely a typo- for invisible read visible- or can you see the steam in the gauge glass above the water?

Charlie D

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