This guide is a short edited extract from
"The Complete guide to Miniature Steam" which is now available on CDrom or Internet download.
The following notes are based on my many years of playing with miniature steam engines.
Coal firing a model boiler is the nearest you will get to the "full size" feel, not to mention the smell!. Whether your boiler is a vertical, horizontal, traction engine or locomotive type boiler, the principle is always the same.
There are a definite sequence of events to be followed, but rule #1 is: "Always watch the water level". This is even more important with coal fired boilers, as you cannot simply turn the heat off like you can with a gas fired boiler.
Lighting up:
Make sure that the boiler is at least half full of water, then using either small pieces of charcoal or wood, soaked in paraffin or white spirit, place a good quantity of this material through the firehole & onto the firebars. When you feel that there is sufficient in there, light a splinter, introduce it into the firehole to light the contents therein. At the same time, as soon as the fire is lit, start the "blower". Keep the firehole door open at this stage, until all the contents are lit, then close the firehole door. You do not need a massive draught, in fact if the blast is too strong, the boiler may be forced, which is not the best idea. Aim to raise the temperature steadily. After a few minutes open the firehole door & take a look at the fire, if it is glowing brightly, then add some pieces of coal. It is important to have the correct size & type of coal. "Anthracite" is normally used, "grains" for small boilers & "beans" for larger ones.
When you have 20psi, remove your blower device & open the steam valve to the steam blower nozzle. Don't forget that from now on, the blower is using the steam so the water level will drop - keep your eye on the water level at all times. When the pressure hits 50psi, it is time to pump some water in so that the water level rises to the top of the gauge. Don't overdo this, or the boiler will "prime" & water will be sent along with the steam to your steam engine. As you pump in the water, you will see the pressure drop, when the pressure drops to 20psi - stop pumping the water & let the boiler recover. Now once again, check the fire - if the fire is all bright, put some more coal on & shut the firehole door. Again you will see a pressure drom from having the door open & introducing new coal. When the pressure rises to around 50psi, pump more water in until the water gauge shows nearly to the top. This time when the boiler recovers its pressure, you are ready to open the regulator to your steam engine.
Basically the sequence is as follows:
MORE WATER - MORE COAL - but NEVER at the same time Boiler pessure nearing blowoff point, engine running well - water a bit down - what should I do? Pump some water in - by whatever means that you have, hand pump, engine driven crankshaft pump, live steam injector or Weir pump. If the water level is ok, put some coal on, but not too much. If the water level is good & the fire is good, then turn down (or turn off) the blower. If the boiler is still about to blow off, then consider opening the firehole door a little, in order to stop the safety valve from blowing off which will waste water. In real terms you will probably not get the sequence right at first & end up with the worst case scenarios: no water - high steam pressure & your water pump won't work! - panic OR EVEN WORSE: no water at all - no steam pressure at all & your water pump still won't work! - panic even more!
In the latter case - EMERCENCY! - immediately put the fire out, - by steadily introducing water into the firebox, onto the fire with a large syringe or similar. Try not to squirt the water onto the internal sides of the firebox, as the sudden contraction could cause the boliler joints to fail in extreme circumstances. Anyway, assuming that the fire is now out, you will now be covered in soot & ash & the steam plant, including the surrounding area will be in a real mess. Needless to say, I cannot recommend any of the above processes to be carried out on the kitchen table or worktop, always run a coal fired boiler steam plant outside. Solution: Find out why you couldn't pump more water into the boiler, and then clean the mess up & start again. Great fun - and a good learning curve too!!!!