What is the minimum diameter for distribution piping?

• A. Not less than 2 inches
• B. Not less than 3 inches
• C. Not less than 4 inches
• D. Not less than 5 inches

Answer: (B)

The size of distribution piping is chosen to carry the needed water flow without causing excessive pressure loss or high outlet velocity as zones operate. A minimum of three inches is used because it provides enough cross-sectional area to deliver the design flow to all sprinkler heads and maintain adequate pressure when multiple zones run, reducing the chance of under-watering at the farthest heads. If you use a smaller pipe, like two inches, the flow can be restricted and the velocity may rise, leading to larger pressure drops and uneven coverage. Larger diameters (four or five inches) would work, but they add unnecessary cost for most landscape irrigation needs without providing a practical benefit in typical designs. Therefore, the recommended minimum is three inches to balance performance and cost.