4.2 Collecting Initial Site/Equipment Data – Sprinkler System

The site for the evaluation should be one that is representative of the system, unless a specific problem site is to be tested. Usually the goal is to get an idea of how the entire system is working. The site must be in one irrigation zone so that the test can be started and stopped for all sprinklers at the same time.

A digital camera is handy for recording the site and the can placement during the test.

The diameter of throw of the nozzle should be recorded along with the operating pressure of the nozzle and the nozzle size. The initial wind speed and direction should be noted just before the test begins. After the test, pressures and wind speed should be noted again. Wind speeds should represent the usual irrigation situation or the test may not be a valid one. It is recommended to measure the wind speed and direction every five minutes and record it for more complete data.


Wind speeds should be as close to usual irrigation time wind speeds as possible to get a true evaluation. If it is windy and usual conditions are not windy because the system normally runs at night, then it is not a good and useful test. On the other hand, winds over about 10 miles per hour (mph) cause considerable distortion of the pattern. Under 5 mph is much better. Frequent, regular interval (every 5 minutes) measurements of wind velocity during the test will give values for calculating an average velocity. Figure 4.2a illustrates a hand held anemometer for measuring wind speed.


Figure 4.2a. A small combination unit that includes an anemometer is handy for measuring wind speed. The other parts of the unit can be used on a ski trip or other sporting event.


Pressures can be measured directly at the nozzle using a pitot tube on a pressure gauge. The small tube is inserted into the end of the nozzle to measure the pressure at the nozzle during its operation. Figure 4.2b illustrates the pitot tube and how to position it in the water stream. Adjust it to get the maximum reading of pressure. An alternative setup for measuring pressure would be to put a pipe tee in line with the sprinkler head and measure the pressure there. Water pressure in a main line can be measured by inserting a pressure gauge into the line with a pipe fixture.



Figure 4.2b. Pitot tube on a pressure gauge is placed 1/8 inch from nozzle to measure pressure. Adjust until highest constant pressure is read. (Source: http://edis.ifas.ufl.edu/images/1492984284 , Univ. of Fl - IFAS AE262 Dec. 2005)

At a minimum, it is highly desirable to have a pressure gauge pre-installed on the zone downstream from the zone valve (solenoid valve) and one pre-installed at the end of the zone to show pressure loss in the zone.

A flow meter is handy for measuring the flow during the test to give an idea before and during the test about the discharge of the sprinklers. The actual recorded flow can later be compared to the expected flow based on the flow meter reading. It is good to know the expected flow so that the length of time for collecting water in the cans can be set. A collection of nozzle discharges can be used to compare to initial specs for the nozzle and to help to find nozzle wear. The set of drill bits should be used to check for nozzle wear on older systems. Compare drill bit fit to the fit on a new nozzle of the same size.

The duration of the test should match the normal operating time of the sprinkler irrigation system. This provides an accurate measure of the uniformity of coverage in a typical irrigation. If the irrigation system is automated and already programmed into the controller, then running the system on its normal schedule is more representative of factual operating conditions. Be sure to time the test period with a stop watch – do not assume the controller is entirely accurate. In fact the stop watch should check the controller for accuracy.

Data Sheet – make a table to include these:

Sprinkler spacing = feet x feet

Diameter of sprinkler coverage (throw) = feet

Initial nozzle pressures: psi

Initial nozzle discharge: gpm

Initial wind speed:

Final nozzle pressures:

Final nozzle discharge:

Final wind speed:

Average wind speed:

Average pressure:

Length of time the system was run for data:


A sample data sheet and Excel file for doing some calculations is shown in Figure 4.2c (pdf) .(.xls file) This form’s page 1 can be printed out for use in recording data in the field during the test. Later the data can be entered into the form on a computer to calculate some of the results. A page 2 will have the calculations on it.



Figure 4.2c. Audit data sheet for overhead sprinklers. Collect initial data before the test and final data after the test. Record the water volume collected in each catch can. Spreadsheet will calculate some values.


Make a sketch of the site, showing the irrigation equipment positions, distances, and noting any crop, slope or terrain factors. Figure 4.2d (.doc) is a worksheet for drawing a map of the test area showing the sprinklers and catch cans. Instructions on the sheet list other items to include. Data from the catch cans (water volumes) should be written on the drawing to show them in their proper location. Later the data points may help to identify problem areas. The form is good but, more practical is graph paper with 4 lines per inch to give a grid of ¼ inch spaces. The graph paper is a very good work sheet for drawing because the paper has a scale to it and lines to guide drawing.


Figure 4.2d. Sample map sheet for showing the test area and data. A few of the details to be included are shown. Simple graph paper is also very good for this task.

A drawing is invaluable for recording the visual record of the test. Show collected water volumes on the map also.