In distribution, part of our role is to support professional contractors by clarifying misconceptions—such as the misconceptions about how much pressure is the correct amount for an irrigation system and its individual zones. Explaining the benefits of properly regulating pressure, and your ability to provide optimal performance to the customer, will save water and lead to healthier landscapes.

Here are a few considerations to assist you in determining proper system pressure, and discussing it with your client:

1. Piping Affects Pressure

When water moves through a pipe, it experiences friction—and this friction causes a loss in pressure. To determine the amount of pressure loss in a system, you need to know the size of the piping used, the volume of water being moved, the distance it is being moved, and have an understanding of the roughness of the pipe—or the microscopic imperfections of the pipe that cause the water moving through the pipe to experience friction, causing pressure to be lost.

With this information, you can find out how much pressure is being lost due to friction by using friction loss charts that are available in the back of any manufacturer's product guide and on their websites.

The velocity of the water is also important. This is the speed at which water is flowing through the pipe, and it is directly related to both the volume and pipe size. As your volume or demand increases, the speed at which the water is moving also increases. A common misunderstanding is that decreasing your pipe size will increase your pressure—this thought can be easily changed by understanding the velocity limitations of your pipe. With plastic pipe, the standard in our industry is to limit the velocity to 5 fps (feet per second); with metal pipe, it is 7.5 fps.

Knowing the velocity limitation of pipe, you can review a friction loss chart and see the maximum flow for each pipe size. With Class 200 PVC pipe, the maximum flows are as follows:

• ½-inch 5-GPM (gallons per minute) at 4.21 fps
• ¾-inch 10-GPM at 4.93 fps
• 1-inch 16-GPM at 4.78 fps

For other pipe sizes and types, just review the available charts. Knowing the flow and velocity of a system, along with the use of friction loss charts, can help you find out how much pressure the irrigation system is losing.

2. Pressure Affects Sprinkler Performance

With a new understanding of pressure loss, it’s now possible to review different types of sprinklers to identify which models will be most effective for your system pressure. If you observe misting from your pop-up spray heads, your system is not irrigating efficiently.

Most spray heads are best operated at 30 PSI, based on manufacturer specifications. At 30 PSI, the water droplets produced are larger and more evenly applied to the landscape. As pressure increases, the water droplets become smaller and more water is discharged through the nozzle. With the change in droplet size, your application becomes uneven, and you begin seeing a lot of overspray caused by wind blowing the water away from the landscape.

Multi-stream multi-trajectory (MSMT) nozzles are best operated between 40-50 PSI, based on manufacturer specifications. These nozzles can accommodate higher pressure before you begin seeing uneven application and drift, but it is still best to keep them at optimal pressure.

Rotors are best operated between 40 PSI upward to 70+, based on the manufacturer and type.

3. Regulating System Pressure

Since each irrigation system is different and has specific pressure requirements, it is important to know what pressure regulation options are available.

We can regulate pressure at the point of connection to ensure inlet pressure does not exceed optimal system capacity. Use this method if you know you have high pressure from the start. You can use a pressure-reducing valve, which can be adjusted to your required pressure. For example, Zurn has the NR3XL series of pressure reducing valves.

Another option is to regulate each individual valve. This is very beneficial if you have several zones with different pressure requirements. Valves can be regulated with the use of pressure reducers such as the Accu-Sync from Hunter or the PRS-Dial from Rain Bird. Pressure reducers allow you to adjust your inlet pressure to fit each zone's unique pressure requirement.

You can also regulate each individual sprinkler head, which is the preferred method as it ensures that only optimal pressure (or below) is used. Pressure regulation at each head is achieved through a pressure regulator installed on the stem of the sprinkler head, like the optional PRS option from Rain Bird or the PRS40 from Hunter. No matter the option you choose, it should regulate your pressure to the optimal operating pressure.

At times it may be advisable to use more than one method of regulation to ensure optimal pressure for all parts of the irrigation system.

4. Benefits of Operating at Optimal Pressure

Operating an irrigation system at optimal pressure not only helps ensure that water is being applied properly and evenly to the landscape, but also reduces the amount of water that is being used. For example, the average flow of a 15H nozzle at 30 PSI is 1.79 GPM (gallons per minute). When the pressure is increased to 40 PSI, the average flow increases to 2.14 GPM. Though the increase of .35 GPM may seem small and insignificant, it can quickly add up.

Let’s say you have a large 8-zone residential property with eight spray heads per zone. If the pressure was regulated and maintained at 30 PSI, then each zone would be applying 14.32 GPM. If the pressure were increased to 40 PSI, you would apply 17.12 GPM—resulting in an increase of 2.8 GPM per zone! If each zone ran for 20 minutes each week, the system would apply 448 gallons more than if the sprinklers were operating at optimal pressure.

The misconception of “good” pressure can easily be changed by simply reviewing manufacturer specifications, and understanding how pipe size affects pressure. Implementing these techniques can save small amounts of water, which over time will add up to substantial amounts.

Proper pressure not only saves water, but reduces the amount of overspray onto sidewalks, patios and other hardscape surfaces, which will reduce liability on commercial properties. Any way you look at it, there are considerable savings and advantages to using proper pressure when operating an irrigation system.