Auxiliary Steam Plant Control
For the burner control to be fully automated transducers must be fitted to monitor such things as fuel and air flow, steam pressure and water levfel. Steam pressure is the main controlling parameter and the controller will adjust fuel to maintain this at a set level .
The water level is monitored and kept within a certain range. Should the level become too low then firing is ceased. Automated restarting after this trip is not allowed and a manual reset must be operated. A high level shut off may also be fitted by tradition tripping the feed supply pumps.
With this system fuel is delivered at a constant rate.Therefore before commencement of firing the fuel may be circulated through the heater so is available at the correct temperature. The diverter valve can deliver a varying quantity of oil to the burner dependent on the master controller signal.
When flashing the fan will operate for a certain period at full flow to purge the furnace of gasses. The spark relay operates and the fuel solenoid opens. A period is allowed for ignition. If the photocell fails to detect a flame at the end of this set period the fuel solenoid is shut down. Depending upon set up a second attempt may be made or an alarm output signal will be generated.
Each item in the system must be tested on a regular basis for correct operation by simulated failures.
This came up in my class one motor paper!!