The most effective types of rain sensors have absorbent discs inside them that swell when they are wet. The swelling interrupts power flow that would normally open a valve and start an irrigation cycle. When the discs dry out, the power is allowed to flow the next time the controller sends a signal.
No. Rain sensors must absorb enough water to swell the discs and cut off the electric signal. Just as it can take a while for the ground to absorb water during a fast rain, it takes a little while for the discs to absorb water. However, if it has been raining for any length of time or has been wet for many days, the rain sensor should keep the system from running.
The best rain sensors have hygroscopic discs inside. There are so many models and brands it would be impossible to list them all. Ask questions about products and any warranty they may include. Also consider if you want a product that allows you to bypass the rain sensor for a maintenance check during a wet period.
If you want an easier installation, there are also wireless types that allow you to install the electrical interrupter right at the controller inside your garage and then the part that responds to rain outside where it will be exposed to weather conditions. Of course these extra features come with increased cost.
We recommend that you visit an irrigation supplier and take with you the brand and model number of your irrigation controller. The staff at the store can then show you different options and explain features and installation requirements.
Professional irrigators get discount rates for purchases of equipment. However, they have labor costs associated with taking the time to find the best product for you and for properly installing it. Discuss with your irrigator what kind you want (wireless types are more expensive) and how much time it will take to install it. The cost will range from $50 to $150 depending on the product selected and challenges of your installation.
That depends on how comfortable you are with wiring, electricity, and digging. The most economical models of rain sensors must be installed on the wires that supply electricity to all of the valves of your irrigation system. These wires run alongside the main pipes that supply water to the valves of the system. It is important to locate the rain sensor where it will interrupt power to all of the valves and not just some of them.
Wireless brands of rain sensors can be simpler to install because they have two parts. One part is installed at the controller to the power wires (no digging) and one part is installed outside where it will be exposed to the rain.
If you think you will have difficulty with installation, consider hiring an irrigation professional. Ask questions about the product being used and request a test after installation is complete. Make sure you can access the rain sensor device for future maintenance or testing. Placing it high in a tree will create challenges in the future
Citizens often alert us when they observe water waste such as irrigation during rain or water running down the street.
When we hear that a site is watering during a rain or immediately after a big rain, we will contact the property owner to determine if a rain sensor is in place and if it works, which may include a site visit. If the property owner has not complied with the requirement to put in a functional rain sensor, then he or she may receive a citation for watering in the rain. (NOTE: Watering on the wrong day or time may result in a citation being issued without prior warning if witnessed in person by an enforcement officer.)