Boiler Pressure Controls
- Operating limit control: Turns the boiler on when required, and off when satisfied.
- Setpoint: Slightly above the highest desired steam pressure, but at least 10% lower than safety valve setting
- High limit control: Used as a safety limit to turn the burner off in case of operating limit control failure. Requires manual reset.
- Setpoint: approximately 10psi above operating limit if feasible. Alternatively, set midway between operating limit and relief valve setting.
- Modulating control: Monitors changes in pressure and signals the modulating motor to increase or decrease firing rate as needed.
- Setpoint: Depends based on the end-user's desired steam pressure, but must be set so that the mod motor returns to low fire before the operating limit control opens. Set its low point below the cut-in setting of the limit control to allow the burner to briefly operate in low fire on each start rather than immediately driving to high fire.