We come across many golf courses that have the original sprinklers from installation. Many are 20-30+ years of age.  Back then the efficiency or Distribution Uniformity (D.U.) of most sprinkler models was nowhere near as good as the sprinklers available today from all of the golf sprinkler manufacturers.  From Toro we see the 630, 660 and 730 series rotors.  Some older courses with Rain Bird still have the 47 & 51 Impact sprinklers. The sprinklers today have less pressure loss through the sprinkler from the swing joint to nozzle.  In addition there are a wider variety of nozzle selections which allow each course to customize nozzle selection.  Although this can be a challenge since each course has different spacing, topography, wind and temperature variations, at least you have many options to test and see what works best.  

Worn nozzles can have a negative effect on D.U. but determining if nozzles are worn requires some flow testing. (Refer to article on website “Projected Flow Versus Actual Flow”)

Low sprinklers or ones not set level to grade are a typical problem and are often the reasons a course may have wet and dry areas.  Over time, the settling of the soils under and around sprinklers does change.  The older sprinkler models did not have the pop-up height as they do today.  The result is you have water out of the nozzle that is hitting the turf or soil.  If the sprinkler is not level the radius of throw will be higher on one side and lower on the other, thereby affecting the D.U.

A nozzle or base filter clogged by a small rock or foreign debris can cause problems.  When this is seen on multiple sprinklers you should look at the filtration system at the pump station to ensure it is working properly.  The other source could be a problem with the intake line that runs from the water source into the pump station.  If there is hole in the intake, algae or pond weeds could be finding its’ way into the system.  Several of our clients have a diver that cleans all intakes on an annual basis.  If you can eliminate these factors as a cause, then evaluate the repair process of the irrigator when an irrigation component needs repair.  We have seen cases where the irrigator did not flush out debris following a lateral or main line break.  If flushing is not thorough or not performed at all, it can result in rocks and debris getting stuck in the hydraulics and ending up in the filters or nozzles.

Sprinklers with built in pressure regulation can and do fail over time.  If they are failing and the result is low pressure, the gallons, profile and radius of throw is greatly affected.  Failure on the high side can lead to a larger radius of throw and in some cases misting out of the nozzles.  There is an allowable variance in regulation from all the sprinkler companies and it is a good idea to know what that variance is.  For the courses with pressure regulating valves (PRV) on the main line, it is recommended that they be serviced or at least evaluated whenever the pump station is serviced. During one audit we discovered a PRV that the new Superintendent did not even know was on the golf course.  It had been buried and not working properly for an unknown number of years.  That same PRV that should have been regulating pressure down to 90PSI had a downstream pressure of 160PSI. The high pressure caused the failure of numerous pressure regulators at the sprinklers.  On many of these sprinklers that were regulated to 65PSI, we measured up to 110PSI out of the nozzles

Pressure Regulating Valve - Lost and Not Serviced	Pressure Regulating Valve - After Replacement

Low pressure on certain areas or the entire course is a big factor and a problem that leads to wet and dry patterns. Main line pressure testing is something we recommend at every golf course.  Typically, pressure and flow is easy to see at the pump station or remotely if your course has the pump software resident in the central.  If pressure is low at the station the problem can usually be rectified by replacing the faulty component at the station.  Testing at high and low elevations across the course is the next step if pressure at the pump station is “normal”. 

Most golf courses have a central computer that runs the irrigation system.  When there are patterns anywhere on the course, evaluation of the database and hydraulics is a good starting point.  We have seen hydraulic flow zones with the main lines not sized correctly.  Others look like they were done in a rush.  As an example, one course had only one zone for the entire golf course. The flow graph below left shows the projected flow during the nightly cycle with only one flow zone.  The graph on the right displays a vast improvement after the hydraulics were changed in the central.

This particular course had two problems.  The hydraulic flow in laterals and the mains were exceeding design specifications for flow and pressure loss.  Too many heads were coming on at the same time on many laterals, thereby causing low pressure. This situation can also cause water hammer at all times during the nightly cycle. Water hammer decreases the life expectancy of the hydraulic components and is one of the causes of main and lateral breaks.

Many courses over time have changed the nozzles or sprinklers on the course.  These changes typically result in higher flows out of the nozzles.  This alone is not a problem but if the database was never changed to reflect the field changes, low pressures and other problems do lead to wet and dry patterns.

On many older systems it is not unusual to have gate valves that no longer work.  If they have failed in the fully open position, it is not a problem until isolation of the hydraulics is needed to make repairs. On a couple of courses we have suspected that the gate valve had failed and was only partially open and possibly fully closed.  Even though we could turn the gate valve key to what we thought was full open, it was obvious that it was not.  Isolation of the mains and gate valves in order to test if a valve is open or closed may be your best option in order to determine if one has failed closed.  On older systems, replacing parts on a gate valve can be difficult due to rust and corrosion. There is no choice but to replace the entire gate valve.  As silly as it may be, sometimes the irrigation staff has simply forgotten to open a gate valve that had been closed for repair work.  We recommend checking each and every gate valve on the golf course.  Exercising the valves by closing and opening them is a good idea but is often not performed because the Superintendent did not want to chance breaking an older valve or it not opening again.  One client who had low pressure suspected that a large rock had entered the main line after a “blow-out” and the rock had been lodged at the valve and was restricting flow.  After a lot of excavation and cutting into the main line, he proved to be right and found a large rock right at the valve.

In the “olden days” of irrigation design it was not uncommon to size a lateral PVC line from 1.5” at the electric valve, then down to 1 ¼ after the first or second head and then down to 1” at the last head or two.  This was done to save money on pipe and fittings but repairing these requires the irrigator to stock and carry an array of different sized parts.  Downsizing pipe is not a big problem for the courses with individual sprinkler control. But for a course with a “block” system it can have a negative effect on pressure.  This is due to the fact that if all 3-4 sprinklers activate at the same time, the flow and pressure loss can exceed what is recommended for that small of a pipe.  We had one client with this exact problem and they asked us to do some testing in order to see if the downsizing of the pipe was the problem for the wet and dry patterns.  The sprinkler closest to the electric valve had good pressure at 75PSI.  Pressure for the second, third and fourth (last head) on the lateral gradually declined and was at 47PSI on the last head.  After capping the first head, the pressure on the last head went up to 60PSI.  After capping two heads, the pressure on the last head increased to 70PSI. These simple tests proved that the pipe sizing was to blame for the low pressure and wet and dry patterns.   There are various solutions to this problem.  Some can be quite costly but have huge benefits and some are not worth the time and money depending upon the age and condition of the irrigation system.  

Poor sprinkler spacing has a monumental effect on D.U. and is a large cause for patterns at many courses.  Correcting poor spacing is a tough challenge since it is time consuming and can be expensive.  Most importantly, understand that moving even one sprinkler can impact D.U.  Testing different nozzles and in some cases changing the sprinkler pressure regulation may help improve conditions.  Testing of this nature is easy to do but it takes time and patience to see what works best.  We recommend nozzle testing on small areas and trying different nozzle combinations on more than one area at a time.  Basically if you have three different fairways with three different nozzle variations you should see what works best within one week if not sooner.

Should you be considering changing sprinklers or just the main nozzles, using bigger nozzles is not always better.  Consideration should be given to existing spacing, main line pressures and infiltration rates.  In a perfect world, head to head coverage across the entire course during the nightly cycle would be ideal.  When the main nozzles throw much further than the surrounding sprinklers, wet areas can develop.  When head to head throw is short, dry patterns can typically be found.  Most Superintendents call dry patterns “donuts” and recently one called them “beauty rings”.  Either way, if you are changing nozzles or sprinklers, we recommend starting with a short Par 4 fairway in order to determine the best nozzle selection for your golf course.

As a golf course ages, different Superintendents come and go. Some may prefer one sprinkler over another and over time this leads to multiple types of sprinklers all over the course. 

On many courses, budget restraints limit how many sprinklers a Superintendent can replace every year.  These new sprinklers are most often used to replace a broken sprinkler rather than all of them installed on the same fairway, green or tee.  A Superintendent may have been given free sprinklers to test out on a fairway or entire hole. The result of any or all of these factors is a variance in D.U. and precipitation rates on a specific hole or across the entire golf course. During our inventory audits, It is  not uncommon to see up to 5-8 different types of sprinklers by different manufacturers.  Every sprinkler has variations in radius, GPM, operating pressure, loss of pressure through the sprinkler and nozzle combinations. If it is fiscally possible, we always recommend replacing all of the sprinklers on a given fairway or an entire golf hole.

Even if many of the older sprinklers are still working, they can be used as your parts resource for other problematic sprinklers.

On far too many golf courses, we see 8-12 sprinklers that activate from one station. This can lead to pressure and distribution problems.  In addition, applying water to only where it is needed is difficult due to a lack of control.  It is easy to surmise that the irrigation staff daisy chained the field station wires together. This was done due to a cut or failed splice.  We give credit for them having made the heads work but we also refer to this as “Fixing the Symptom of the Problem”  Wire tracking and fault location equipment should have been used to track and repair the problem wire.

Have an addition to this list, please let me know.

If you would like to discuss this question and the answers more in depth, please call

Craig at (415) 342-1030 or email at This email address is being protected from spambots. You need JavaScript enabled to view it.