The number of bubblers an irrigation zone can support is calculated based on the water supply’s capacity and the bubblers’ consumption rate. Bubblers are low-volume, high-flow emitters designed to deliver water quickly and directly to a plant’s root zone, making them suitable for deep watering of individual trees and shrubs. An irrigation “zone” is a group of bubblers controlled by a single valve. Its size is limited by the amount of water that can flow through that valve and the connected pipes. Determining the available water supply is the first step, as it sets the absolute boundary for the entire system.
Establishing the Water Supply Baseline
The primary constraint on any irrigation zone is the available flow rate from the water source, measured in Gallons Per Minute (GPM). This flow rate represents the total volume of water the system can physically move. A simple way to measure this flow is through the “bucket test,” which involves timing how long it takes to fill a container of a known volume, such as a five-gallon bucket, from the outside spigot.
To calculate your actual GPM, divide the bucket volume by the number of seconds it took to fill, and then multiply that result by 60. For example, if it takes 30 seconds to fill a five-gallon bucket, the calculation is (5 / 30) 60, which equals 10 GPM. This result is the absolute maximum flow rate available to your entire system.
Pressure, measured in Pounds Per Square Inch (PSI), represents the force pushing the water through the pipes. Static pressure is the force when no water is moving, measured using a gauge attached to an outdoor spigot. Working pressure is the pressure when water is flowing, and it is always lower than static pressure due to friction within the pipes. Although most residential systems operate between 40 to 80 PSI, the flow rate (GPM) is the immediate limiting factor for calculating the number of bubblers.
Flow Requirements for Bubbler Emitters
Bubbler emitters are rated by their water consumption, typically expressed in Gallons Per Hour (GPH). Flow rates can range from 0.5 GPH for small plants up to 10 GPH or more for large trees. This consumption rate represents the demand side of the calculation, which must be balanced against the supply capacity measured in GPM.
Bubblers come in two main types: fixed-flow and adjustable. Fixed-flow bubblers maintain a consistent, manufacturer-specified GPH rate, offering certainty in design calculations. Adjustable bubblers allow manual flow rate changes, which provides flexibility but introduces variability that must be accounted for.
To match the bubblers’ consumption (GPH) with the water supply’s capacity (GPM), you must convert the bubblers’ GPH rating into GPM. This conversion is straightforward: divide the bubbler’s GPH by 60, since there are 60 minutes in an hour. For instance, a bubbler rated at 60 GPH consumes 1 GPM (60 GPH / 60 = 1 GPM).
Calculating the Maximum Bubblers Per Zone
The theoretical maximum number of bubblers per zone is determined by dividing the total available GPM from the water source by the GPM required for each bubbler. This calculation provides the absolute limit for the zone’s capacity. For example, if available flow is 10 GPM and each bubbler requires 1 GPM, the theoretical maximum is 10 bubblers (10 GPM / 1 GPM = 10 bubblers).
Designing a system to its theoretical maximum is not recommended because it leaves no room for pressure fluctuations or system wear. Applying a safety margin to the available GPM is a crucial step. Most irrigation professionals recommend using only 80% to 90% of your measured available GPM to ensure consistent performance across the zone.
If your available GPM is 10, using an 80% safety margin means your design flow rate is 8 GPM (10 GPM 0.80). Continuing the example of a 1 GPM bubbler, your practical maximum number of bubblers per zone would be 8 (8 GPM / 1 GPM = 8 bubblers). This margin helps maintain adequate pressure for all bubblers, especially those furthest from the valve.
Impact of Pipe Size and System Layout
The theoretical limit calculated using the available GPM is constrained by the physical characteristics of the pipes, fittings, and valves. As water moves through the system, it encounters resistance, causing a loss of pressure known as friction loss. This pressure drop increases significantly with the length of the pipe and the velocity of the water moving through it.
The diameter of the pipe is the most significant factor affecting friction loss. Smaller pipes force the water to move faster to deliver the same volume, greatly increasing turbulence and pressure loss. For instance, a 3/4-inch pipe should not be subjected to flows exceeding 7 to 8 GPM to keep the water velocity below the recommended maximum of five feet per second. Exceeding this limit causes excessive friction loss and potential damage.
Even if your water source provides 15 GPM, you cannot design a zone to use that full flow if the pipe running from the valve is only 3/4 inch. In this scenario, the pipe size limits the usable flow for that zone to 7 or 8 GPM, overriding the higher capacity of the water meter. Proper design requires sizing the main lateral lines to handle the total calculated GPM demand while keeping water velocity low to minimize friction loss. This ensures the last bubbler receives the necessary working pressure.