Flow Sensors Made Simple

Flow sensors may seem complicated but can actually be explained simply.  Breaks in irrigation systems waste vast amounts of water every year.  Flow sensors are affordable devices that can be installed to detect and automatically shut down the irrigation system when breaks, malfunctions or vandalism occur.  Flow sensors can be designed and installed during construction, or can be part of a retro-fit project.  Either way, flow sensing should be part of any large irrigation system.

I think of flow sensors as odometers for irrigation systems.  They measure the amount of water passing through an irrigation line, and communicate that information to the controller. Not every controller accepts information from a flow sensor; therefore, I suggest selecting the controller first.  The controller manufacturer will recommend the best flow sensors to use with their product. In most cases, it is best to use a normally open master valve when using a flow sensor.

There are many flow sensors to choose from, and the basic operation of each is similar. Flow sensors are set to memorize the normal flow of your system.  Most manufacturers recommend two full irrigation cycles as a minimum to learn what the normal flow is.  The operator is able to program the controller to shut the master valve off if the flow is a certain percentage (to be determined by operator) over the memorized amount.  Some controllers allow the same feature for too little flow.  Operators are notified when there is a shut down in the system.  Typically the system will shut down for a period of time (say 10 minutes) and then open the master valve again.  For example, you have a break in zone one that was detected within the first two minutes of operation.  Watering time for zone one this day is 15 minutes.  The master valve would come on again after 10 minutes; high flow would be detected again, and the valve would be shut off again for 10 minutes.  When the master valve comes back on, zone one will have passed its water time. The valve will be shut and additional zones will be watered.

Flow sensors on retro-fit projects can be expensive because the sensor must be wired to the controller and may require trenching through concrete or asphalt.  Advances are being made in wireless flow sensors, but prices are high. A wired flow sensor can be purchased for less than $400. In comparison, a wireless flow sensor costs around $3000. Installation cost many times dictates when a wireless sensor is needed.

Finally, there is a new product on the market combining the master valve with the flow sensor.  Netafim makes one called the Globe Hydrometer.  Combining the master valve with the sensor can reduce installation costs, and can be especially helpful when the installation area is tight.  List price for the 2” Globe Hydrometer is $1185.

Understanding and using flow sensors is an important tool for saving our precious water.