Sprinkler Nozzles

A sprinkler nozzle turns mains or pump pressure into a pattern of droplets spread across a fixed radius. The job looks simple until you try to make every head in a zone throw the same distance on the same pressure — then radius, arc and trajectory stop being catalogue trivia and become the difference between even coverage and a lawn with brown rings.

This is the irrigation and greenscape side of spray nozzles: lower pressure than process duties, larger throw distances, and a pattern chosen for ground coverage rather than surface wetting.

Radius, Arc and Trajectory

Radius is how far the wetted pattern reaches, set by the nozzle orifice and the supply pressure. Two heads on the same zone must throw the same radius or the overlap is wrong and you get dry wedges.

Arc is the sector the head covers — full circle for open areas, fixed or adjustable partial arcs for corners and edges. Mixing arc types without rebalancing flow is the usual cause of a zone that over-waters one spot and starves another.

Trajectory is the launch angle. Low-trajectory nozzles throw under wind and past obstacles; high-trajectory types clear taller crop or shrub but drift more in wind. The choice is set by what is between the head and the ground it has to cover.

Fixed Spray Versus Rotary

Fixed-spray (sometimes called spray) nozzles throw a continuous fan or cone out to a short radius, typically a few metres. They suit small zones and tight layouts but need higher pressure to hold the pattern and lose a lot to evaporation on hot days.

Rotary (rotor) nozzles throw streams that rotate, covering a much larger radius at lower pressure per unit area. They are the right call for larger turf and for water-efficient design, because the slower application rate lets the soil absorb instead of running off.

The mistake is fitting rotary heads into a small zone designed for fixed spray, or vice versa — the radius and precipitation rate no longer match the pipe and the pressure.

Matching to Water Pressure

Sprinkler nozzles are rated at a reference pressure (commonly 2 bar) and radius falls as pressure drops. A zone supplied by a weak pump throws short and develops dry rings; the fix is usually a pressure-regulated header or a smaller-orifice nozzle set, not a bigger pump.

Flow scales with pressure, so a pressure swing also changes how much water each zone draws — relevant wherever the supply is metered or shared with other uses.

Reference Specifications

Radius and flow below are quoted at 2 bar. Trajectory is the launch angle class.

How to Select a Sprinkler Nozzle

• Zone size and shape — sets radius and arc; match every head in the zone to the same radius.
• Supply pressure at the head — not at the pump; friction loss in the pipe matters.
• Fixed spray versus rotary — small tight zones favour fixed spray, large turf favours rotary for efficiency.
• Trajectory versus obstacles — low for wind and clearance, high for taller crop.
• Precipitation rate balance — all heads in a zone should apply water at the same rate or some areas flood while others dry.
• Maintenance reality — screens clog with grit; a dirty screen throws short and creates the dry ring people blame on the nozzle.

Frequently Asked Questions

Why does my sprinkler zone have brown rings? Almost always a radius mismatch or a clogged screen dropping pressure at one head. The pattern is telling you the heads are not throwing the same distance.

Fixed spray or rotary for a small lawn? Fixed spray for small, tightly laid-out zones; rotary for anything large enough that the lower application rate and bigger radius save water.

Why does radius drop on hot afternoons? Evaporation loss on fixed-spray nozzles, plus any pressure sag from simultaneous use. Rotary nozzles suffer less because they apply more slowly.

Can I mix arc types in one zone? Only if you rebalance flow and radius so every head still wets the same area at the same rate. Unbalanced arcs are a common over/under-watering cause.