PSI vs GPM in Irrigation Design: Add Nozzle Flows, Watch Pipe Friction

Sprinkler Nozzle GPM Adds Up; Pipe Size Manages Pressure Loss

User asks: if one head is 2 GPM at 40 PSI, do two heads each still get 2 GPM?

Yes—Nozzle Flow Is Fixed at Given Pressure

• 1 head @ 2 GPM = 2 GPM zone.
• 4 heads @ 2 GPM = 8 GPM zone.
• Each head's flow depends on pressure at that head.

The Pipe Friction Trap

Too-small pipe → pressure drops along run → last head gets less pressure → less flow → poor coverage.

Rule of Thumb

For 10 GPM zone: use 1" pipe throughout. Keeps velocity low, friction loss minimal. Only a few fitting types needed.

Design Sequence

1. Determine available GPM (from meter/test). 2. Choose nozzles (e.g., 2.0 GPM rotors). 3. Max heads = Available GPM ÷ Nozzle GPM. 4. Size pipe for zone GPM (1" for ≤15 GPM).