When it comes to wiring a wood fired boiler or biomass steam boiler, keep it simple, stupid. There is no need for expensive controls to monitor the flame as are required with fossil fuel burning boilers. With an oil or gas boiler, if the flame were to go out, it would soon become catastrophic if the fuel source were not also shut off. No such danger exists with a wood fired boiler, as it will simply begin to lose steam pressure as it cools down.
Our boiler electrical system serves to open and close a horizontally configured guillotine-type air shutter to maintain a constant pressure in the boiler, and also to open a solenoid dump valve to release excess pressure should it rise slightly above the set point. It should go without saying not to depend on an electrically operated solenoid for over pressure protection, so additionally there is a 5 psi mechanical relief valve installed into the system.
Wood fired Steam Boiler-Sequence of Operation and Testing Procedure
1. Connect power to the unit and verify the air intake solenoid has pulled the air shutter open.
2. Fill the boiler with water to the fill line and ensure the McDonnell Miller 247-2 has stopped the flow of water into the boiler.
3. Open one or more steam valves to the atmosphere to prevent the unit building pressure.
4. Build a fire in the firebox and wait for the boiler to begin building steam.
5. Once you've checked for leaks, close the valves to the atmosphere and open the supply valve to your load(s).
6. As pressure begins to build, observe the pressure gauges to ensure no overpressure condition occurs.
7. As pressure approaches the operating point of 1 psi, check and adjust the operating pressure controller as required so that it opens the circuit to the air shutter solenoid. A spring will close the air shutter and the pressure should begin to drop slowly.
8. When the pressure drops by approximately .2 psi, the mercury bulb will tilt the other way, re-energizing relay PC1 and...