The Long and Short of Matched Precipitation Rates

Hunter offers a wide range of spray nozzles for just about every type of application—we have Pro-Spray fixed pattern nozzles, adjustable arc nozzles, and a wide range of specialty nozzles. And these nozzles cover distances from as large as 15 feet all the way down to the shortest of our short radius nozzles at 2 feet.

As is the case with our rotor nozzles, we strive for the best matched precipitation rate possible (how efficiently the amount of water applied over a given area is matched by adjacent sprinklers on the same zone).

But, short radius nozzles and long radius nozzles have different precip rates. If designed on the same zone, they will have to run for the same amount of time. This means that the higher precip rate heads will put down more water than the lower precip heads. This will lead to overwatering in some areas to ensure sufficient watering in others.

Plus, when opening sizes in the nozzles are dropped to reduce flow to the required level, dirt tolerance issues arise.

For example, a 15H nozzle typically provides water at 1.5" per hour. For a 2H nozzle to match this rate, the flow would have to reduce to .03 gallons per minute. A single-hole opening at 50 PSI would have to be .032" in size to restrict water to that flow. That is a hole only about three time larger than the size of the period at the end this sentence.

To avoid issues with the presence of sand or other particles, nozzles have been designed to provide a higher application rate. This permits particles to pass through without getting lodged in the nozzle and disrupting the pattern.

In a nutshell, it is virtually impossible to achieve matched precipitation rates at a small radius. If anyone tells you otherwise, they’re pulling your leg.

At Hunter we try to design as many of our nozzles as possible to have similar precip rates, providing designers with the maximum in flexibility when laying out their irrigation. However, there are limits that are unavoidable.