Expanding an existing PVC irrigation system to cover a newly landscaped area or improve coverage efficiency is a common home improvement project. This process requires methodical preparation and an understanding of the system’s plumbing principles. Before starting, the main water supply must be completely shut off at the backflow preventer or main valve. Failure to isolate the system can result in a high-pressure water release. This guide provides a step-by-step approach for integrating a new sprinkler head into an existing zone.
Planning and Gathering Materials
Precise planning is the initial step, starting with determining the optimal placement of the new head for maximum coverage overlap. Homeowners must calculate the required flow rate, measured in gallons per minute (GPM), that the new head will demand. Adding too much GPM can drop the pressure below the recommended operating range, leading to poor performance across all heads. This calculation determines if the zone can support the addition without compromising hydraulic integrity.
The necessary materials include the appropriate type of sprinkler head (rotor or spray), PVC pipe matching the existing lateral line diameter, and required fittings. A standard PVC T-fitting is often used for a direct tie-in, though a saddle tee may be an option. Tools should include specialized PVC pipe cutters for clean, square cuts, and a supply of PVC primer and solvent cement for the solvent welding process. Selecting the correct primer and cement, matched to the pipe’s schedule, ensures a strong, watertight bond that resists high pressure.
Tapping into the Existing Supply Line
After planning, the work begins by accurately locating the existing PVC supply line where the new head will connect. Once the pipe’s path is determined, a sufficient access trench must be excavated around the pipe for comfortable working space and clean cuts. The trench should provide access to at least a foot of pipe on either side of the planned connection point. Before cutting, the entire zone must be drained completely by opening a bleed valve or end cap, ensuring no residual water remains that would compromise the solvent welding process.
If using a standard T-fitting, two precise, square cuts must be made in the pipe, spaced to match the T-fitting’s dimensions. Using a specialized pipe cutter ensures the cuts are perpendicular to the pipe’s axis, which is necessary for a proper fitting seat. The cut ends of the existing pipe and the interior sockets of the new T-fitting must then be thoroughly cleaned and prepared using PVC primer. The primer chemically softens the PVC surface, preparing it to fuse with the solvent cement.
Immediately following the primer application, a uniform layer of solvent cement is applied to both the outside of the existing pipe ends and the inside of the fitting sockets. The T-fitting must be pushed onto the pipe quickly and firmly, engaging the pipe fully until it bottoms out. A slight twist during insertion helps distribute the cement evenly and ensures a chemical weld. The fitting must be held in place for approximately 30 seconds to prevent internal pressure from pushing it off before the initial bond sets.
The T-fitting must be oriented correctly, with the new outlet facing the planned lateral run, before the cement begins to cure. Once set, the joint requires a minimum of several hours, typically two hours, before low-pressure testing. It requires a full 24 hours before it should be fully repressurized. This curing time allows the chemical bond to develop maximum strength, preventing joint failure under operating pressure.
Connecting the New Lateral and Sprinkler Head
With the T-fitting securely installed and cured, the next step involves running the new lateral pipe to the designated location of the sprinkler head. Accurate measurement of the distance is performed, and the new PVC pipe is cut to length, accounting for insertion depth into the T-fitting and subsequent fittings. The pipe is then joined to the open port of the T-fitting using the same primer and solvent cement technique, ensuring a strong, watertight connection.
The new lateral pipe must be extended directly beneath the intended location of the sprinkler head. A terminal fitting, such as an elbow, is then solvent-welded to the end of the pipe. From this fitting, a riser assembly is installed to connect the lateral line to the sprinkler head. The use of a flexible pipe connection or a swing joint is recommended. This assembly absorbs minor shifts in the soil and prevents stress fractures on the rigid PVC pipe caused by maintenance or ground settling.
Before the final head is attached, the new lateral line should be thoroughly flushed to clear any dirt, stones, or PVC shavings that entered during the cutting and gluing process. This is done by briefly turning the water on while the end of the riser assembly is uncapped, allowing debris to be expelled under pressure. Failing to flush the line can lead to immediate clogging or damage to the internal mechanisms of the new sprinkler head.
After flushing, the final sprinkler head is screwed onto the riser assembly, often using plumber’s tape on the threads to ensure a seal. The head should be installed so its top sits flush with the surrounding finished grade once the trench is backfilled. This elevation allows the head to operate without obstruction, ensuring the spray pattern is maintained as designed. The final step is to ensure the cap is securely fastened, ready for the system’s test run.
Testing the Zone and Restoring Pressure
The final stage is systematic testing of the modified zone to validate the integrity of all connections and hydraulic performance. The main water supply must be turned back on slowly to allow the system to gradually fill and purge air without creating a sudden pressure surge, known as a water hammer. A slow repressurization minimizes stress on the newly cured solvent welds.
Once the system is under static pressure, a thorough inspection for leaks is performed at every new connection point, particularly the T-fitting and the base of the new riser assembly. Even a slow weep indicates a compromised weld that must be repaired before proceeding. After confirming the absence of leaks, the zone can be activated via the controller for a full cycle.
During the test cycle, the spray pattern and arc of the new sprinkler head must be adjusted to match the required coverage area. The nozzle should be set to deliver water uniformly without overspraying paved areas or structures. Simultaneously, the performance of all other heads in the zone should be monitored. This confirms that the addition has not significantly reduced the operating pressure or flow rate of the existing components.
If the zone’s overall performance remains acceptable, confirming the initial GPM calculation was accurate, the trenches can be carefully backfilled. The soil should be compacted gently around the pipe to provide support and prevent future settling that could stress the connections. The new system is now fully integrated and ready for use.