Do you suspect a pressure problem with an irrigation system—or would you like to see if a system is performing to spec?

Having enough water pressure is key to making any irrigation system function the way it was designed to. That's why so many irrigation issues can be traced back to having excessive or low water pressure.

Whether you need to inspect a new or old system, here are a few fundamental steps to follow as you look for potential pressure problems.

1. Have the right tools on hand.

First, having a few simple tools will make your troubleshooting  efforts much easier:

• Pressure gauge - For measuring water pressure in pounds per square inch (psi)
  Hunter MP Gauge Tee Adaptor

• Hose bib adaptor - For taking pressure readings at a hose bib
• Pitot tube - For taking pressure reading at a rotary nozzle
• Pressure gauge adaptor tee - To measure nozzle pressure on spray bodies
• Measuring wheel - To measure distance/spacing between sprinklers
• Irrigation multitool - For making quick adjustments or repairs

When selecting a pressure gauge, choose one with the pressures you anticipate to fall to the middle of the range, rather than the high or low end, said Ewing Education instructor, Tom Glazener.

That means if you are routinely measuring 15-30 psi, then a 60 psi gauge is probably appropriate.

Most irrigation needs can be handled with the 0-100 psi gauge, but if you are measuring high static pressures, a 200 psi gauge may necessary. However, resist the temptation to make a high range gauge work for all cases!

2. Perform a static water pressure test at the source.

Your static water pressure is the pressure your system has when the irrigation system is off, at rest or not running. Ideally you should do this test when pressure is probably at its lowest (usually in the morning) or when the system is normally scheduled to run.

Where to check static water pressure:

• Hose bib. Using your pressure gauge with a hose bib adapter, you can check the pressure at a hose bib or another unregulated connection point.
• Backflow preventer or pressure regulator. Test the pressure on the upstream side of the device at the first test cock.

Many times pressure regulators are placed on systems that already have low pressure where they aren't necessary, so it's important to note the static pressure upstream. You should also test downstream of the device and turn the system on to ensure there isn't any excessive pressure loss that could indicate a problem or blockage in the device. (Some pressure loss is normal here—see the system loss potential for backflow devices in Section 4 below.)

If this process isn't familiar to you, this video will show you how to test water pressure at a backflow device and what to look for: 

3. Check your emitter operating pressure requirements.

In general, there are three main types of emitters and their pressure requirements tend to fall into these ranges:

Drip Emitters               15-40 psi

Spray Heads                 20-40 psi

Rotary Heads               30-90 psi

As most irrigation pros know, the specific operating pressure requirements for any drip emitter or sprinkler varies by manufacturer and model. Manufacturer catalogs or your smartphone can be helpful for finding the specific pressure requirements for the emitters being used on site.

4. Understand the total system loss potential. 

When an irrigation system is running, it automatically begins to lose water pressure due to friction as water moves through it. For an average residential system, this is about 15-25 psi loss on a typical residential rotary sprinkler system, from the water supply to the last head:

• 5 psi loss through the meter
• 4 psi loss through the backflow device (DCA or PVB)
  • 14 psi loss for a reduced pressure backflow device
• 3 psi loss through the zone valve
• 2 psi loss through the mainline
• 1 psi loss in the lateral line

Depending on where you took your static pressure reading, you can subtract what you expect the system total loss to be from your static water pressure to determine what the operating pressure at the furthest head should be. (Keep in mind, this is a rule of thumb and your actual system total loss may vary!)

[box size="large"](Static Water Pressure) – (System Total Loss) = Operating Pressure at Furthest Head[/box]

Now you can compare the operating pressure to the manufacturer requirements for your nozzles to see if it falls within the acceptable range. Of course, if it is too low or high, it's almost certain the system will perform poorly.

5. Measure your working nozzle pressure.

What you expect the operating pressure to be and the actual working water pressure at the nozzle could be different due to poor design, leaks, a clogged valve or another problem with the system.

To check the working pressure, test the furthest zone from the point of connection or the “worst‐case” zone: the largest zone, the zone with the most elevation change or one that is experiencing problems.

Large turf sites sometimes have multiple valves running from the same point of connection, which would also impact operating pressure. Be sure to test these areas under normal operating conditions.

Testing PSI at the Nozzle

1. Find the last sprinkler head on the zone you are testing.
2. Attach your pitot tube to your pressure gauge or connect your gauge and adapter tee to the spray head.
3. Turn on the zone and head over to the sprinkler you are measuring. Note: Be prepared to get wet!
4. For rotary heads: Hold the pitot tube in the water stream, about 1/4-inch away from nozzle for an accurate pressure reading. For spray heads: Read the pressure gauge.

Once you know the pressure at the nozzle, you can compare it to what you expected and to the manufacturer’s specs.

While you’re at it, test the first head on the zone, too. The pressure shouldn’t vary more than 10% from first sprinkler to the last in each zone to maintain good performance. If it does, you could have an issue with your sprinkler spacing or lateral pipe sizing.

Note: You may also want to check to see if you have mixed nozzle arcs (full, half and part circle) on the zone. Many times, even with matched precipitation rate nozzles, it can be difficult to achieve even coverage with full circle and part circle nozzles on one zone.

Is the pressure high?

If all reading are pointing to your system having too much pressure, you'll need to look at some possible solutions like pressure regulators, flow control valves or pressure regulating spray heads, says Ewing Account Manager, Doug Donahue. In this video, Doug demonstrates one of those potential solutions, pressure regulating spray heads:

6. Check your sprinkler spacing.

Grab that measuring wheel, and check your sprinkler spacing against the manufacturer recommendations. If after any possible nozzle adjustments and barring any major obstructions or problems upstream, you still aren’t getting proper head-to-head coverage, you’ll need to look some possible options to increase system pressure.