Splitting an existing sprinkler zone separates a single irrigation area into two distinct zones, each controlled by its own valve. Homeowners typically split a zone when the original design stresses the water supply, resulting in low pressure across too many sprinkler heads. This pressure drop causes poor coverage and uneven watering, often leaving parts of the lawn or garden dry. Splitting a zone is also necessary when different areas, such as grass and flower beds, are combined on one line but require drastically different watering times. The goal is to reduce the total water volume (GPM) required for each smaller zone so the system can operate efficiently.
Preliminary Assessment and Preparation
Before starting any excavation, assess the system’s capacity to ensure the split solves the pressure problem. Determine the total available water flow rate (GPM) by timing how long it takes to fill a five-gallon bucket from an outdoor faucet. This total flow must be greater than the combined GPM required by all sprinkler heads in the two new zones. For example, if system capacity is 16 GPM, each new zone should ideally require less than 8 GPM to account for pipe friction loss and ensure adequate pressure.
Before cutting into the system, shut off the main water supply and power down the controller to avoid electrical hazards. Depressurize the system by briefly opening a valve or drain cap to relieve residual pressure. Gather all necessary materials, including the new solenoid valve, appropriate PVC or poly pipe fittings, primer, and solvent cement, to prevent unnecessary delays once the pipe is cut.
Plumbing Modification: Adding the New Valve
The physical process begins with excavating the area where the existing lateral line will be split. This location should be easily accessible and allow the pipe run to be logically divided to separate the sprinkler heads into two groups. Once the pipe is exposed, cut the existing lateral line cleanly at the chosen split point using a specialized cutter. Remove the cut section to allow for the insertion of a new T-fitting.
Install the T-fitting into the cut line to create a branch. One side continues the original zone’s pipe run, and the new branch connects to the added solenoid valve, controlling water flow to the new, smaller zone. All new PVC pipe connections require a two-step chemical process: applying primer to soften the surface, then quickly applying solvent cement. Push the parts together and hold them firmly for about 30 seconds to allow the cement to bond. Allow the connections to cure for the manufacturer’s recommended time, often several hours, before repressurizing. The pipe section leading to the new zone’s sprinkler heads connects to the outlet side of the new valve.
Electrical Connection and Controller Setup
Making the new valve functional requires running low-voltage wiring back to the main irrigation controller. The new solenoid valve has two wires. One wire must be spliced into the system’s common wire, which is typically white and shared by all other zone valves. All outdoor wire splices should be made using waterproof connectors, such as silicone-filled wire nuts or grease-filled caps, to prevent corrosion and ensure a reliable electrical signal.
The second wire from the new solenoid is the dedicated zone wire, which must be run back to the controller box. Connect this wire to an unused, numbered terminal on the controller, which will now correspond to the new zone. The controller operates on low voltage (usually 24 volts AC), but the power should remain off during the wiring process. After connecting the dedicated wire and ensuring the common wire is secured to the terminal labeled “C” or “Com,” the controller can be powered on. The final step is accessing the controller’s programming menu to assign the new terminal a station number and set its unique watering schedule and duration.
System Testing and Fine-Tuning
Once the plumbing and electrical connections are complete, slowly repressurize the system to check for leaks before backfilling the trench. Turn the main water supply on gradually, allowing water to fill the pipes and valves. Closely observe all new glued joints and threaded connections. Any sign of dripping or spraying water at a joint indicates a failed connection that must be repaired immediately.
With the system fully pressurized, manually run the new zone from the controller to confirm the new valve activates and only the intended sprinkler heads operate. The original zone should also be tested to ensure the split has not negatively impacted its function. Fine-tuning involves observing the spray patterns and coverage from the sprinkler heads in both zones. The increased pressure from the split will likely require head adjustments to achieve optimal coverage and uniform water distribution.