How should a valve be selected for a zone in terms of flow rating?

• A. Choose a valve with a flow rating that equals or exceeds the zone's maximum GPM, with some safety margin.
• B. Choose a valve based on color of pipe.
• C. Choose the smallest valve regardless of zone.
• D. Choose any valve rated for 10 GPM.

Answer: (D)

Sizing a valve for a zone means making sure the valve can handle the zone’s peak water demand with a reasonable safety margin. The valve’s flow rating should be at least the maximum flow the zone may use when all emitters are open, plus a buffer to account for small variations in pressure, emitter flow, and operating conditions. If the valve is too small, you’ll restrict flow and the zone won’t irrigate properly. If it’s larger than needed, you still want sensible control, but the primary risk is under-sizing rather than over-sizing. Other options miss the point because pipe color has no bearing on flow, choosing the smallest valve can fail to meet demand, and picking a valve based on an arbitrary fixed rating ignores the zone’s actual needs and variation.