A successful, efficient sprinkler system relies on meticulous pre-installation planning to ensure optimal performance. This preparation determines the system’s ability to deliver the correct amount of water across the landscape. Proper planning avoids common issues like uneven coverage and prevents component failure caused by improper water pressure or flow. By calculating the system’s needs against the available water supply, the design minimizes water waste and maximizes the longevity of the hardware.
Assessing Water Supply and Property Layout
The foundational step in planning is to create a detailed map of the property and then conduct a water audit to determine the available supply. Begin by sketching the yard, marking all boundaries, structures, and existing permanent obstacles like large trees or walkways. This map should also identify areas with different sun exposure, soil types, and plant needs, as these factors will influence the final watering schedule and head selection.
The water audit requires measuring two critical values at the point where the system will connect to the main supply line. First, static water pressure (PSI) is the pressure of water when it is at rest, tested using a pressure gauge screwed onto an outdoor spigot with all other water sources shut off. This reading establishes the maximum pressure available for the system.
Second, the flow rate (GPM) dictates the maximum volume of water the system can use at any one time. This is measured using the “bucket test,” where a container of known volume is timed while filling completely from the source. The GPM is calculated by dividing the volume by the time in minutes, which provides the absolute limit for the entire system. Designing an irrigation system that demands more GPM than is available will result in significant pressure loss and poor performance.
Designing the Zones and Head Placement
The GPM and PSI data collected directly influences how the property must be divided into distinct hydraulic zones. A zone is a group of sprinkler heads that operate simultaneously off a single valve, and its total GPM requirement must not exceed the available flow rate. Different types of sprinkler heads, such as high-flow rotors and low-flow spray heads, must be separated into their own zones because they require different operating pressures and delivery rates.
The most crucial principle for even water distribution is “head-to-head” coverage. This means the spray from one sprinkler head must reach the location of the adjacent head. This overlap ensures that the water delivered to any spot on the lawn is uniform, preventing dry spots. To achieve this, the spacing between heads should be no more than the published radius of the sprinkler head.
Selecting Sprinkler Heads
Selecting the appropriate sprinkler head depends on the size and shape of the area to be covered. Rotors deliver water over a long distance in a rotating stream, suitable for expansive lawns with a throw radius of 20 to 70 feet. Fixed spray heads are better for smaller, irregularly shaped areas and have a shorter throw, usually between 4 and 15 feet. Areas with shrubs, flower beds, or vegetable gardens should be assigned to a drip irrigation zone, as this method delivers water directly to the plant root zone at a low flow rate, minimizing evaporation.
Selecting System Components and Sizing Pipes
Once the zones and head placements are finalized, the required hardware must be specified, starting with the control components. The system requires electric solenoid valves, typically arranged in a manifold, with one valve corresponding to each zone. These valves are connected to a central controller or timer, which dictates the watering schedule and the duration for each zone.
Pipe sizing is determined by the maximum GPM required by the largest zone in the design to minimize pressure loss from friction. The mainline, which is always pressurized, and the lateral lines, which only pressurize when their zone is active, must be sized to keep the water velocity below the recommended maximum of five feet per second (5 fps). Exceeding this velocity significantly increases friction loss, lowering the pressure available at the sprinkler heads.
For example, if a zone requires 12 GPM, a one-inch diameter PVC pipe is often appropriate for the lateral lines, depending on the specific pipe material and the total length of the run. Using a pipe diameter that is too small for the calculated flow rate will starve the heads farthest from the valve, causing them to spray weakly. The chosen pipe type, such as Schedule 40 PVC for its durability or Class 200 for its cost-effectiveness, must be consistent with the system’s pressure demands.
Finalizing Documentation and Materials List
The final planning phase involves creating comprehensive documentation to guide the installation and serve as a reference for future maintenance. A final, scaled map must be produced, accurately illustrating the location of all trenches, the diameter of the pipe used in each section, the exact placement of every sprinkler head, and the position of the valve boxes. This map is the blueprint for the entire project.
A detailed Bill of Materials (BOM) is then compiled, listing every component. This itemized list ensures that all necessary parts are purchased and that the budget is accurately estimated.
- The number of sprinkler heads by type
- The length and size of all pipe sections
- All required fittings like elbows and tees
- Specific backflow prevention devices
Before any purchase or digging begins, check local municipal codes. These codes often mandate the installation of specific backflow prevention devices and may require a permit for trenching or connecting to the main water line.