CSI: Irrigation

Brian Vinchesi

Do you keep track of how many pipe and fitting breaks you have on your irrigation system on an annual basis? Do you separate mainline breaks from lateral line breaks? Or is a break a break? If you don’t, you might consider starting. Knowing how many breaks your irrigation infrastructure is having and where they are occurring will help you figure out how to prevent them.

Most superintendents consider irrigation breaks to be a normal part of golf course maintenance, and that’s a problem. Maintenance staffs are reactive with pipe and fitting repairs. If you want to stop and have fewer breaks, you need to be proactive. You need to determine why the pipe or fitting broke and take steps to keep it from happening again.

Short of digging through the pipe or fitting with a piece of excavating equipment, the reason for a failure will most likely not be obvious. However, the type of break will provide some information. For example, if the fitting pulled out at a solvent-weld (glued) joint, it is most likely age or not the best cementing process when it was installed. If there is a crack in the hoop of a PVC elbow or fitting, either cemented or gasket, the fitting has probably life cycled out. Pin holes in ductile iron fittings are caused in the manufacturing process but take time under pressure to show up. Cracked fittings on threaded joints are from overtightening.

You will have to do some analysis to determine the cause of breaks that are not as easy to identify. Pressure and velocity are the two places to start a pipe analysis. Test pressures with a pressure gauge inserted into a quick coupler in the vicinity of where you are having issues. A pressure gauge never lies and will tell you what is going on at that exact point where it is inserted. Read the gauge and compare it to your pump station operating pressure. Turn on and off some sprinklers and see how much the gauge moves around. Lots of movement back and forth is not good. Note what maximum pressure the gauge hits. Check your pump station to make sure it hasn’t had any high-pressure alarms and if your pump station monitoring software tracks pressure, look at the graph for high pressures. Remember that high pressure breaks things. Velocity also breaks things, especially fittings, but it is a little more difficult to figure out.

The Irrigation Association has friction loss/velocity charts on its website (bit.ly/1v0oogV) for most types of irrigation pipe. To use the charts, you need to know what type of pipe you have and some idea of how much water is flowing through it. Flow is obtained by multiplying the number of sprinklers that are turned on, fed by the pipe in question, multiplied by the gallonage. If your sprinklers use 33 gallons per minute each and you had eight on a 4-inch, Class 200 PVC pipe, the chart for Class 200 PVC pipe would tell you the velocity is approximately 6.58 feet per second (fps). Plastic irrigation pipe (PVC or HDPE) is not supposed to exceed a velocity of 5 fps, so in this case, the velocity could be causing issues. It may not be a problem if it was a onetime occurrence, but because it has a set schedule in golf irrigation, everything gets repeated, so the high velocity over time (many years) will cause issues.

Pipe and fitting breaks on mainlines are not as common as on laterals unless it was a bad installation. Mainline pipe is installed deeper and rarely has glued joints. The pipe is also trenched in as opposed to pulled which allows the trench to be inspected before pipe installation and to be carefully placed in the trench. Newer irrigation systems use fittings that are much stronger than PVC so they have fewer failures. Pulling pipe during installation of laterals can cause issues long term as you cannot see the pipe being installed and it can rub up against rocks or other obstacles as it installs weakening the pipe. When you look at the repair, it will exhibit a long crack or small hole where it slid along or was installed up against a rock during installation.

Brian Vinchesi, the 2009 EPA WaterSense Irrigation Partner of the Year, is president of Irrigation Consulting Inc., a golf course irrigation design and consulting firm headquartered in Pepperell, Mass., that designs irrigation systems throughout the world. He can be reached at bvinchesi@irrigationconsulting.com or 978/433-8972.