03-10-2009, 04:08 PM
nachoman Wrote:Is this combustion air reglulated by any sort of damper? Or is it smiply a gap above the ashpan?
I am speaking in regards to steam traction engines here. That is where I have a lot of experience in the 1:1 scale. There is most certainly dampers over these air intakes. This allows the fireman to control how much air is getting in. If the engine is working hard there will most likely be a big fire going to keep the pressure up. When the engine comes to a stop suddenly the fire is much too large for the amount of steam that is needed. This causes the pressure to build up. Eventually it reaches the point where the pressure relief values must lift, this is a waste of water. By closing the dampers when stopped it essentially blankets the fire and causes it to smolder away. Thus not burning as hot. Then once the engine is back underway it is possible to open the dampers and the fire that has been smoldering away will roar to life as it suddenly has lots of access to oxygen.
Hope this helps.
Mike