Automated irrigation systems rely on electric solenoid valves to control water flow. The standard design uses a one-to-one relationship, where a single valve controls water delivery to a single, distinct landscape zone. This setup allows for precise control over watering schedules for areas with different plant or sun exposure requirements. While this dedicated approach is industry best practice, it is technically possible to manage two zones with a single valve. However, this consolidation introduces significant complexities in system hydraulics and electrical control, making it generally impractical for optimal irrigation.
The Short Answer to Dual Zone Control
The motivation for controlling two zones with one valve often stems from the desire to save money or conserve limited station capacity on an existing controller. A direct method, sometimes called “ganging” or “splitting” zones, connects two separate zone pipes to the output of a single electric valve. For this configuration to function, the two combined zones must be physically small and have nearly identical water flow requirements, measured in gallons per minute (GPM).
The total water demand of both zones running simultaneously must not exceed the maximum flow rate capacity of the supply line and the controlling valve. Mismatched zones—such as combining a high-flow rotor zone with a low-flow spray zone—will result in an unbalanced system. The area with the lower pressure requirement will receive excess water, while the other zone will be starved, leading to poor coverage and dry spots.
Combining Zones Using Flow Diverters
A more structured method for a single valve to manage multiple zones uses a specialized mechanical component known as an indexing valve or flow diverter. Unlike the direct approach, the flow diverter allows a single electric valve to control water delivery to zones sequentially. The diverter is installed downstream of the solenoid valve and uses water pressure to mechanically route the flow to different outputs.
The diverter cycles water flow to the next zone each time the main electric valve is activated, runs, and is then deactivated, causing a momentary pressure drop. This pressure drop allows an internal mechanism to rotate and index to the next output port. For example, the first time the valve turns on, it waters Zone A; when it turns off and back on, it advances to Zone B.
Programming the controller requires only one station terminal to activate the single electric valve. However, the run time programmed must be the cumulative watering time required for all zones combined. This sequential nature eliminates the ability to customize watering days or durations for individual zones, which is a significant drawback for varied landscapes.
Addressing Pressure and Flow Constraints
The primary technical challenge in dual-zone control is managing the hydraulic consequences, specifically the loss of water pressure and flow rate. Any component added to the water path, including a flow diverter, creates resistance that results in a reduction of pressure, known as head loss. This pressure drop is composed of both major losses from friction within the pipes and minor losses caused by fittings, elbows, and the internal mechanisms of the diverter valve itself.
Insufficient pressure or a reduced flow rate (GPM) directly compromises the performance of the sprinkler heads. If the pressure drops too low, the heads will not achieve their intended throw distance, leading to poor spray patterns and inadequate coverage. This creates localized dry areas, particularly at the edges of the watering pattern. A properly designed system must ensure that the pressure at the most distant sprinkler head remains above the minimum operating pressure required for that specific head type.
Even with a sequential flow diverter, the system must meet the pressure and flow demands of the largest single zone connected to the diverter. The added resistance from the diverter’s mechanical components contributes to the overall head loss, making it more difficult to maintain optimal pressure compared to a system using dedicated, standard electric valves. System performance is directly tied to the total amount of resistance the water encounters before reaching the sprinkler heads.
Essential Wiring and Controller Considerations
When using a flow diverter, the electrical setup is simplified because only the single electric valve feeding the diverter needs to be wired to a station terminal on the controller. Conversely, running two standard electric solenoid valves simultaneously from one station requires connecting them in parallel. This parallel wiring combines the electrical draw of both solenoids onto a single terminal, which introduces a significant risk of electrical failure.
A typical electric solenoid valve draws an inrush current of around 300 to 400 milliamps (mA) to open. Most residential irrigation controllers have a maximum output limit per station, often around 700 to 900 mA, to protect the internal circuitry. Wiring two solenoids to one station can easily exceed this amperage limit, especially if a master valve is also used, potentially causing the controller’s fuse to blow or activating its internal overcurrent protection.
For successful operation with a flow diverter, the controller must be capable of simple on/off cycling of the single station. The precision of the watering schedule relies entirely on the mechanical reliability of the diverter to index correctly each time the water flow is stopped and restarted. Any failure in the indexing mechanism can result in one zone being skipped or perpetually watered, leading to immediate irrigation problems.