Given the data for a second lift station, what is the most likely cause of the problem?

Given the data for a second lift station, what is the most likely cause of the problem?

• A. Lag pump is closed
• B. Lag pump is air-bound
• C. Lead pump is air-bound
• D. Force main pressure too high

Answer: (C)

Air binding in a centrifugal pump happens when air gets trapped in the pump casing or suction/discharge piping, preventing the impeller from moving water properly. In a two-pump lift station, the lead pump is expected to do the heavy lifting; when it is air-bound, it can’t develop the required discharge head, so overall flow drops and the station behaves as if it is not pumping at full capacity. The data for the second lift station would show the lead pump running but not delivering expected flow, with signs like poor discharge, possible air pockets or gurgling in the discharge line, and a system that cannot build adequate pressure despite the pump running. This matches a scenario where the primary pump cannot prime or maintain flow because air is in the line, rather than a simple mechanical shutdown or an overpressurized discharge. If the lag pump were the problem, you’d expect symptoms centered on the lag unit’s performance, not the lead unit, and a closed lag pump would stop flow entirely regardless of the lead’s condition. A force main pressure being too high would show elevated discharge pressures or backpressure, which isn’t indicated by the observed data.

Air binding in a centrifugal pump happens when air gets trapped in the pump casing or suction/discharge piping, preventing the impeller from moving water properly. In a two-pump lift station, the lead pump is expected to do the heavy lifting; when it is air-bound, it can’t develop the required discharge head, so overall flow drops and the station behaves as if it is not pumping at full capacity. The data for the second lift station would show the lead pump running but not delivering expected flow, with signs like poor discharge, possible air pockets or gurgling in the discharge line, and a system that cannot build adequate pressure despite the pump running. This matches a scenario where the primary pump cannot prime or maintain flow because air is in the line, rather than a simple mechanical shutdown or an overpressurized discharge.

If the lag pump were the problem, you’d expect symptoms centered on the lag unit’s performance, not the lead unit, and a closed lag pump would stop flow entirely regardless of the lead’s condition. A force main pressure being too high would show elevated discharge pressures or backpressure, which isn’t indicated by the observed data.