This boiler uses an airtight combustion chamber. The only means for air to enter is via the automated air intake mechanism on the bottom. The door is opened by a solenoid, which is controlled by the pressure switch. If pressure drops in the boiler, it opens the air intake to heat up the firebox, raising the pressure in the boiler. If the pressure rises 1/4 psi above the setpoint, an electrically controlled dump valve opens to vent excess steam from the boiler. This provides for near perfectly stable pressure, regardless of whether the firebox is fully loaded or not.
Combustion air enters the front of the unit, and then drops down and passes below the firebox, before entering into the combustion chamber from the rear of the unit. Passing the air through a plenum under the firebox super-heats the air before being introduced, providing for a much hotter and cleaner burning flame. Secondary air intakes are located directly above the fire and provide heated air to the tips of the flames to complete combustion and reduce smoke.
This thing has enough power to supply steam to ten operations the size of mine. I have it throttled down to less than 5% power and still need to dump steam from time to time to prevent overpressure.
These pictures are pretty much in the order the construction proceeded. Most are self-explanatory.
