Buzz
Main Points to Remember
- Oscillating sprinklers operate with a straightforward mechanism: water flows into a spray arm equipped with multiple nozzles or holes. A heart-shaped cam drives the arm to move back and forth, ensuring even water coverage across the spray area.
- The heart-shaped cam guarantees that the water is distributed evenly from the center to both ends of the spray pattern, avoiding the uneven watering that a circular cam might cause.
- This sprinkler type is favored for garden and lawn maintenance because of its simplicity, efficiency, and ability to cover large areas evenly.
During the summer heat and dryness, if you have a lawn, you'll inevitably need to bring out the sprinkler at some point...
An oscillating sprinkler, such as the one depicted here, is one of the most commonly used sprinklers. It creates a fan-shaped spray of water, and the metal arm moves back and forth to cover a rectangular area, typically around 20 feet by 30 feet (6 meters by 9 meters).
If you've spent more than a few moments thinking about it, you've likely wondered what makes the arm of an oscillating sprinkler move back and forth. In this edition of Mytour, you'll discover exactly how it works!
Fundamentals of Oscillating Sprinklers
Here's an example of a typical oscillating sprinkler you can find at most discount or home improvement stores, usually for just a few dollars:
You attach the hose to a connector on the right side (not visible here). There’s typically a knob to adjust the spray pattern (full, center, left, or right):
Connected to the knob is a small arm that is pushed and pulled by a heart-shaped cam. As the sprinkler operates, the cam rotates slowly — about once per minute (rpm) — causing the arm to oscillate back and forth.
The spray arm itself is a hollow aluminum tube with perforations (some sprinklers feature nozzles on this tube):
The spray arm is fitted with a ferrule and an O-ring seal, which allow it to screw into the main body of the sprinkler.
At its core, this device is very simple. Water flows into the spray arm — the aluminum tube — and is sprayed out through the holes or nozzles. The cam moves the spray arm back and forth. Why use a heart-shaped cam instead of a regular crankshaft? The reason is that a circular crankshaft would result in the ends of the spray pattern receiving more water than the center. Think of a piston moving up and down in an internal-combustion engine — it moves slowest at each end and fastest at the center of the cylinder. The spray arm would experience a similar issue, but the heart-shaped cam corrects this imbalance.
How the Sprinkler Cam Spins
The main challenge here is rotating the cam. One possible solution would be to use a small electric motor, but that would require frequent battery replacements, which is not ideal. Luckily, there's a built-in power source: the flowing water that passes through the sprinkler. You could use it in the same way a hydro-electric dam uses water to turn its turbines.
If you cut open the sprinkler's body, you’ll see this is exactly how it functions. Inside, there is a small turbine, or water wheel:
Looking down the tube where the hose connects, you’ll spot a small restrictor that directs some water straight ahead, while forcing a portion of it to shoot left. It’s the water shooting to the left that powers the turbine:
Sprinkler Gear Mechanism
This gear system reduces speed by a factor of 512-to-1, making the cam rotate at about 1 rpm.
Numerous types of sprinklers harness water power in the same way. Some are jet-powered rather than turbine-powered, but all use the force of flowing water to generate either linear or rotational movement. In theory, you could build a small water-turbine generator and attach it to your hose, producing a few watts of power — enough to light a flashlight bulb while watering your lawn at night!
