Automatic sprinkler system controllers are programmed to turn on and off on a certain day and at a certain time. The controller does not know if it is sunny and dry outside or if it is raining. For this reason, all lawn sprinkler systems must have a rain sensor.
The sensor determines whether or not it has rained enough to skip an irrigation cycle. There are three basic types of rain sensors. They all serve the same purpose: to prevent your system from over-watering your lawn or garden. How does it do that? The electrical connection between the sensor and your sprinkler system controller is broken when a certain amount of rain activates the device. The sensor breaks the electrical connection so electricity cannot flow to sprinkler valves or a pump start (if your system is in a well with no pressure tank).
One guy breaks the connection by weighing the water into a rain collection cup. The problem with this type is that leaves, sticks or the occasional gecko will find their way into the collection cup and thus shut down the system.
The next type uses electrodes to determine how much water is in the collection cup. This type of rain sensor device also has a problem of collecting things other than rain in the collection cup.
The most common type of rain sensor used by professionals is the expansion disk device. This type of sensor does not use a collection cup; instead, rain causes the cork discs to expand. This device uses a pressure switch to break the electrical connection. These can be adjusted in ¼” increments to the desired rain fall setting. This setting is typically set to turn off the sprinklers after ½” of rain has fallen.
The most important aspect of installing a rain sensor is where to place it. It should be installed in an area that is not obstructed by trees, drop ceilings, or anything else that might prevent rain from reaching the sensor. If it is a wired sensor, the location is usually near the sprinkler controller. The wires must be connected inside the controller valve wiring panel. This allows for easier system electrical troubleshooting as the sensor can be easily disconnected.
In recent years, FM wireless rain sensors have become very popular. Although more expensive than hardwired devices, the ease of installation and increased placement options more than offset the cost. Most wireless units come with bypass switches built into the device. Some digital controllers also offer bypass options for both wired devices and wireless rain sensors.
No matter what type of rain sensor you choose, all rain sensors offer many advantages over not adding this detector to your automatic sprinkler system. Some of the immediate and long-term benefits include:
or save money. Whether you pay for city water or spend electricity running a pump, the money you save over time will be more than enough to pay for your rain sensor.
o Extends the life of the sprinkler system. Irrigation systems are made up of moving parts. If the parts of the system are used less frequently (during the rainy season), they last longer.
o Protects Water Resources. By limiting the overuse of your sprinkler system, rain sensors reduce excess water runoff that carries fertilizers and pest control chemicals into our shared water supply.
o Conserve Water. Less water is wasted when less supplemental water is needed for your lawn and garden.
How much money can you save with a rain sensor device?
It will vary based on your water source (city, reclamation, or well) and where you live (water costs, electric rate, weather). Here is an example that demonstrates the benefits listed above:
Seminole County, Florida.
System description:
o Designed to irrigate a quarter acre of lawn and timed to apply ½” of water each time the system is run.
o This program would equal 6,788 gallons per irrigation cycle.
o This system (at City Water) pays $2.30 per thousand gallons.
o Every time the rain sensor interrupts a spray cycle, you would save $15.61
According to a recent study in Florida, the use of a rain-sensing device averaged a 45% water savings for single-family residential water use.
The next time you see a sprinkler system running in the rain, you’ll know it doesn’t have to be that way. Rain sensors are affordable solutions to conserve our water, protect our water resources, and save you money.
