How a sprinkler is built: anatomy and internal components

The outer body and retractable stem

A popup sprinkler consists of a cylindrical housing (body) that stays fixed in the ground and an inner stem that rises during irrigation and retracts when pressure drops. The body is made from UV-resistant plastic — usually ABS or reinforced PVC — with a 1/2" or 3/4" threaded inlet at the bottom.

Pop-up height (stem travel above ground) typically ranges from 5 cm (low-profile, for frequently mown lawns) to 15 cm (tall, needed where high grass or plants could block distribution). For model selection see /blog/irrigatori-spray-popup-migliori for sprays and /blog/irrigatori-rotori-popup-migliori for rotors.

The internal filter: the most neglected component

Inside the body, just above the inlet, sits a mesh filter (strainer). Its job is to catch sand, debris and lime scale before they reach the nozzle. A clogged filter can reduce output by 30–50%, causing dry patches in the lawn.

Clean the filter at least once a year, ideally at season end before winterisation. Unscrew the stem counter-clockwise: the ring-shaped filter slides off easily. Rinse under running water and reinstall. For the full winter shutdown procedure see /blog/manutenzione-impianto-irrigazione-inverno.

The check valve (anti-drain)

The check valve is a small elastomeric membrane at the base of the stem. It opens under pressure (when the zone activates) and closes when pressure drops, preventing water from draining back into the pipe or leaking out when the zone is off.

Without a check valve, water remaining in sloped pipes drains through the lowest sprinklers at the end of every cycle, flooding low points and leaving the pipes empty (causing water hammer on the next start). The check valve is built into the stem and is not separately replaceable: if it fails, replace the whole stem.

The nozzle: where distribution happens

The nozzle is the interchangeable part screwed onto the top of the stem. It determines distribution sector (90°, 120°, 180°, 270°, 360°), radius and flow rate. The main manufacturers (Rain Bird, Hunter, Toro) use a standard thread, making nozzles interchangeable across many body models.

Two adjustments are available: rotating the small side deflector changes the sector angle; turning the radius adjustment screw reduces throw by up to 25% without changing nozzles. This adjustment is critical to avoid watering walls or paths. For nozzle selection guidance see /blog/come-scegliere-ugelli-irrigatori-prato.

The return spring and deflector

At the base of the stem sits a stainless steel coil spring that pulls the stem back into its retracted position when pressure drops. If the stem stays partially extended after the zone closes, the spring is worn and the whole stem assembly should be replaced.

The deflector (splash guard) is the top fin that directs water coming out of the nozzle. On some models it is fixed; on others it is orientable. On rotor models the deflector is what creates the slow rotation — water strikes it and transfers angular momentum.

When to replace parts vs. replace everything

Blocked or broken nozzle: replace the nozzle only (€1–3). Stem that will not retract: replace stem and spring (€3–8). Cracked body or damaged thread: replace the whole body (€5–15). O-ring leaking at ground level: replace the O-ring (under €1).

On systems older than 10–12 years it is worth replacing all bodies at once: plastic ages and becomes brittle, and replacing individual broken parts leads to ongoing failures. Keep a stock of spare nozzles and a few O-rings — they fix 90% of problems in 5 minutes.

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