________ settings on the pressure controls are normally staggered so boilers can lead and lag.

• A. Differential
• B. Overpressure
• C. Calibration
• D. Hysteresis

Answer: (A)

Staggering lead and lag is achieved by using the differential setting on the pressure controls. The differential is the deadband between the pressure at which a boiler turns on (cut-in) and the pressure at which it turns off (cut-out). By assigning slightly different differentials to each boiler, they don’t all fire at the same pressure. One boiler will lead as demand increases, while others lag, taking over as pressure changes. This gives smoother operation, even wear, and better reliability.

If the differential is too small, boilers may all fire together and cycle rapidly; if it’s too large, pressure can swing more and load sharing can become uneven. Overpressure, calibration, and hysteresis describe other concepts that don’t specifically create the staggered lead/lag sequence.