How a buried valve, a plunger and a rubber diaphragm switch on your lawn sprinklers
When an underground sprinkler zone springs to life, the trigger is tiny. A magnetised solenoid lifts a small stainless steel plunger, letting water bleed off the top of a rubber diaphragm. The pressure trapped below then shoves the diaphragm up, and water rushes out through the pipes to every head in that zone.
Sprinkler irrigation aims to imitate rain, spreading water through a network of pumps, valves, pipes and heads. Buried systems group their heads into zones, each governed by one solenoid valve and often run on timers. Downstream pipes tend to be PVC for higher-pressure commercial layouts and polyethylene for lower-pressure home ones. At the far end sit fixed spray heads that throw a set pattern about 1.5 to 2 metres, rotating heads that send a broken stream 6 to 12 metres, or drip emitters that feed delicate flowers and shrubs slowly. Retractable heads sink out of the way so mowers do not smash them.
Farms took a while to adapt. Early farmers borrowed home and golf-course equipment, but buried pipes and fixed heads got in the way of ploughing and cost a lot to maintain. Frank Zybach, a farmer in Strasburg, Colorado, invented centre-pivot irrigation in 1940. In the 1950s the Portland, Oregon firm Stout-Wyss developed a rolling-pipe system in which big wheels carry sprinkler-lined pipes slowly across a field, which became the most popular choice for large acreage. Australians in the same decade could buy Nomad's set-and-forget tractor sprinkler, which used water pressure to creep across a lawn on its own.
At the heavy end, rainguns resemble oversized impact sprinklers, running at 2.8 to 9.0 bar and pushing 3 to 76 litres a second through nozzles 10 to 50 millimetres wide. Besides watering crops they suppress dust and serve in logging. Newer systems vary the water they deliver from spot to spot according to soil and plant conditions, guided by rain sensors, soil moisture probes and smart controllers.
Ordinary hoses carry a less obvious concern. A 2017 report found that spray nozzles can create droplets under 10 micrometres, small enough to inhale, and that warm water sitting in a hose can grow Legionella bacteria in biofilms. Cases of Legionnaires' disease and Pontiac fever have been linked to such aerosols.
Source: Irrigation sprinkler
