Irrigation Flow Testing

Why should the irrigation professional conduct a "flow test" prior to designing or installing an irrigation system? There are two main reasons to conduct a flow test prior to design or installation.

WHAT KIND? First of all, the flow test will tell you what kind of sprinkler head you can use by telling you how much static water pressure is available for the irrigation system. Static Pressure is the measurement of water pressure when water is at rest. The Flow Test Gauge will let you know how much static pressure is available. This information is significant because it will immediately tell you what type of sprinklers you can use on the system. Example: If you are designing a system for a residential turf area and were planning to use Rain Bird 1804 popups with 15 foot spacing to irrigate the turf, your static pressure reading would have to exceed the minimum pressure requirement of the sprinkler (30psi) if the system is to operate efficiently.

The reason your static pressure reading would need to exceed 30 psi, (in this case by approximately 10-20 psi if you are reading the pressure at the job site hose bib) is due to the pressure loss the system will experience once the water is subjected to the influences of dynamic water pressure or working pressure. Once water is moving (dynamic), pressure losses as the water flows through backflow devices and valves.

HOW MANY? The second bit of information the Flow Test will provide is how many sprinklers you will be able to put on a single circuit (valve). We determine the number of sprinklers by calculating the volume of water the system is capable of delivering to the sprinkler heads. Water volume is generally measured as GPM or gallons per minute. In our previous example, the 15-foot radius 1804 sprinkler requires 30 psi. The 15H or half circle nozzle also requires 1.85gpm for optimum efficiency. If you planned on placing twenty 15h sprinklers on the circuit, your flow requirement for that circuit would be at least 37 GPM. (20 x 1.85)

To get a flow reading from your Flow Gauge, take a 5-gallon bucket and place it below the flow device. Open the ball valve and measure how much time it takes the fill the bucket. As an example, if it takes 10 seconds to fill the 5-gallon bucket, the maximum GPM the system would be capable of delivering would be 30. (5 gallons x 6-10 second intervals) Your 20-sprinkler head system would not operate properly under these conditions. If, however, the bucket was filled in 6 seconds, you would know you had 50 GPM available and your system would work.