Final answer:
In high-low fire or modulating control boilers, the Low Fire Switch and High Fire Switch control the burner firing rate. The switches also interact with the damper motor to regulate the airflow into the boiler based on the firing rate.
Step-by-step explanation:
In boilers controlled by high-low fire or modulating control with damper motors, the Low Fire Switch and the High Fire Switch are used to control the firing rate of the burner. The Low Fire Switch is activated when the demand for heat is low, and it sets the burner to operate at a lower firing rate. This helps to maintain a stable temperature and prevent overheating. The High Fire Switch, on the other hand, is activated when the demand for heat is high, and it sets the burner to operate at a higher firing rate to meet the increased demand.
These switches are also connected to the damper motor, which controls the opening and closing of the damper. In high-low fire or modulating control systems, the damper is used to regulate the airflow into the boiler. The low fire switch signals the damper motor to open the damper partially when the burner is operating at a low firing rate, while the high fire switch signals the damper motor to open the damper fully when the burner is operating at a high firing rate. By adjusting the damper position according to the burner firing rate, the system can optimize combustion efficiency.