Pumps, Storage, and Distribution System Operations
Pumps
Centrifugal pumps are the distribution workhorse; their head-capacity curve intersects the system curve at the operating point. Positive displacement pumps are constant-flow and require a pressure relief valve. Deep-well turbine and submersible pumps set suction conditions. NPSH available must exceed NPSH required or the pump cavitates - noise, vibration, pitting, and falling flow. Affinity laws: flow varies with speed, head with speed squared, power with speed cubed. Head and pressure convert at 1 psi = 2.31 ft of head.
Storage
Elevated tanks, standpipes, ground tanks, and hydropneumatic tanks provide pressure, fire flow, emergency reserve, and contact time. Storage size and turnover matter: long detention means old water, low residual, and nitrification or biofilm growth. Float valves, altitude valves, and level controls isolate and refill tanks; level setpoints drive pump cycling.
Distribution
Maintain positive pressure everywhere (roughly 20 psi minimum; typical service 40–80 psi). Use pressure-reducing valves to protect low zones, air-release and vacuum valves to control surge and water hammer, and backflow assemblies with air gaps to prevent cross-connections. During main repair, keep the trench and pipe clean, disinfect, flush, and sample before returning to service; AWWA standard practice is roughly 25 mg/L free chlorine for 24 hours. Unidirectional flushing scours sediment without wasting water.
Traps
Confusing series (heads add) with parallel (flows add) pump arrangements; using gpm where gpd is required; and forgetting that pump power rises with the cube of speed.
Worked example
Brake horsepower = (gpm × head, ft) ÷ (3960 × efficiency). For 500 gpm at 100 ft and 70% efficiency: 50,000 ÷ (3960 × 0.70) = 18.0 hp.