New Water Pump Pressure Drops When Water Flows: Capacity Issue

Diagnosing Pump Pressure Collapse Under Load

A newly installed water pump builds to 50 PSI static but drops to 15 PSI when water is used, not recovering until flow stops.

Root Cause: Demand Exceeds Pump Capacity

The pump cannot supply enough volume (GPM) to meet the system's demand at the desired pressure. This is a pump-to-system mismatch, not a defect.

Diagnostic Steps

1. Check for leaks or stuck-open valves — isolate zones, verify no unintended flow
2. Calculate total GPM demand — sum all nozzle GPM ratings for simultaneously operating heads
3. Compare to pump curve — at 15 PSI, what GPM does your pump actually deliver?
4. Solutions: Reduce heads per zone, install larger pump, or add pressure tank with CSV (cycle stop valve)

For irrigation, zones should be designed so total GPM demand is 80-90% of pump capacity at operating pressure.