Source Flow and Related System Requirements

• System Requirements
• Simple Initial Water Source Determination
• Example 1: What Flow Is Anticipated from an Average Valve?
• Example 2: What Flow is Anticipated from Your Most Demanding Valves?

We recommend reviewing your estimated water source flow, as well as the related size requirements of all equipment related to this anticipated flow. This includes the sizes of the water meter, service line, mainline, backflow device, and remote control valves. This relationship is indicated on the Irrigation Design Rules of Thumb “Max Source Flow and Requirements.”

The Land F/X Source Data tool provides an analysis of your project's water source. For more information, visit our Source Data documentation section.

System Requirements

An interplay of these values may give you an idea of the best possible combination of equipment so you can focus on the most efficient water source flow for the entire combination of equipment.

Simple Initial Water Source Determination

It's a good idea to develop an understanding of the water source and system requirements that may be necessary for your project before you are deeply committed to a design. The examples detailed below reflect a quick review process of determining the supply necessary for a simple project, where only one valve will be operated at one time. In these examples, we assume a project with no constraints as to the time to water (or watering window). We also assume that this is a new project where you can pick the water meter size of your choice. If the site has an existing water meter and service line, these items could be your limiting factors.

These rules of thumb are meant to provide an initial understanding of the source and system requirements that may be necessary. After you complete your design, you may need to develop the precise source and system requirements further.

What is the total flow of your design?

To avoid having to lay out all your heads and determining your total flow; simply use our Schematic Irrigation tool and define the areas where you want different types of heads. Then run a flow total from the Circuiting function. The Schematic Irrigation function provides an estimate of the flow, but it is extremely fast and accurate, and is close enough for a quick initial estimation of water demand. You can also lay out all your heads and run a flow total from the Circuiting function, but this process could turn out to be time consuming.

For this example, we will assume you have a mix of spray and rotor heads with a total flow of 970 gpm (3,670 l/m).

How many stations does the controller allow?

Controllers tend to have up to 12, 24, 36, 42, or even 48 stations for conventional wiring. Two-wire systems can have up to 200 stations or more, depending on the brand. For this example, one valve will be operating at a time, so the number of stations represents the maximum number of valves. You can experiment with different numbers of stations (valves) and how these numbers relate to how much water you may need on average for each valve.

For this example, we will start with 24 to 36 stations, but that number might be flexible.

Example 1: What Flow Is Anticipated from an Average Valve?

Divide the flow by a reasonable number of valve stations to see what approximate flow you might expect from each valve if you split the system equally between them. In this case, 970 gpm (3,670 l/m) divided by 24 stations will result in about 40.4 gpm (153 l/m) per valve, and 36 stations at about 27 gpm (102 l/m) per valve.

What do these flow rates translate to for the source? A 1-inch (25 mm) water meter allows a maximum flow of 37.5 gpm (142 l/m), and a 1 1/2-inch (40 mm) water meter allows a maximum flow of 75 gpm (283 l/m). Divide the total flow by that allowed by the source: A 1-inch (25 mm) water meter would require a minimum of 26 valves, and a 1 1/2-inch (40 mm) water meter would require a minimum 13 valves.

You'll most likely run a smaller flow on some of the valves, such as only for shade areas, etc., so the above numbers are the minimum number of valves, which you will probably exceed by about 20 to 30%. If we factor in this 30%, we would need about 17 to 34 valves, depending on the source.

Assuming you have no watering window limitations, and the plant hydro-zones are satisfied with the source limitations, the most efficient system could be a 1-inch (25 mm) water meter with a maximum flow of 37.5 gpm (142 l/m), with the anticipation of about 26 to 34 stations required at the controller.

Meter sizes have a direct connection to cost, and this varies for different cities or agencies. The difference between a 1-inch (25 mm) and a 1 1/2-inch (40 mm) meter might be many thousands of dollars, so check on these costs and get the most efficient size meter you can.

What are the other system requirements for your source?

For the estimated source demand, what are the related limitations of the remote control valves, mainline pipe, and backflow device?

The 1-inch (25 mm) water meter allows a maximum flow of 37.5 gpm (142 l/m), and the Remote Control Valve table above indicates that a 1 1/2-inch (40 mm) valve is necessary for flows exceeding 30 gpm (113 l/m), so expect to use primarily 1-inch (25 mm) valves with a possible mix of some 1 1/2-inch (40 mm) valves.

The Mainline Pipe table above indicates that at the velocity of 5 fps (1.52 m/s) a mainline of 1 1/2 inches (40 mm) would allow a flow of 32 gpm (121 l/m) and a 2-inch (50 mm) mainline would allow 50 gpm (189 l/m). Therefore, if you desire a maximum flow from your source of the full 37.5 gpm (142 l/m), anticipate having a 2-inch (50 mm) mainline size for most of the mainline.

The Backflow table indicates that a 1-inch (25mm) backflow would allow 48 gpm (182 l/m), so anticipate a backflow of that size.

In this example, you may very well have a 2-inch (50 mm) mainline connected to a 1-inch (25 mm) backflow device. This is extremely common and efficient. In fact, a 1-inch (25 mm) backflow with the flow of 37.5 gpm (142 l/m) will have a pressure loss of about 11 psi (0,76 bars), and a 2-inch (50 mm) backflow with the same flow will have a greater loss, that being about 13 psi (0,90 bars). Therefore, it's important to make an efficient match between backflow size and flow amount.

The service line in the street to your meter may be the limiting factor. A 1-inch (25 mm) PVC service line would have a maximum flow of between 20 and 24 gpm (76 to 90 l/m). This is far less than the 1-inch (25 mm) water meter flow available, so a larger service line would be in order. A 1 1/2-inch (40 mm) PVC service line would allow 40 to 48 gpm (151 to 181 l/m), which exceeds the water meter maximum of 37.5 gpm (142 l/m). Thus, this size service line will allow the full potential flow of your meter.

Example 2: What Flow is Anticipated from Your Most Demanding Valves?

What if the above project has a demanding valve requirement, such as that of a sports field with rotors? In this example, a soccer field is planned that requires 570 gpm (2,158 l/m) of your total flow. How many valves would you want to feed it, what is the expected flow per rotor, and how many rotors would you typically want on any one valve? For example, if your rotor type required 10 to 12 gpm (38 to 45 l/m) and you wanted about five to six rotors per valve, the demand for a typical valve in this sports field would range from 50 to 72 gpm (190 to 272 l/m). Compare that with the 1- and 1 1/2-inch (25 and 40 mm) water meters above; the 1 1/2-inch (40 mm) meter with a 75 gpm (283 l/m) flow appears to be the minimum size water meter that will function efficiently. The 570 gpm (2,158 l/m) total flow at the sports field divided by the maximum 75 gpm (283 l/m) would translate to a minimum of 8 to 12 valves just for the field itself. The entire flow for the rest of this example project is 400 gpm (1,514 l/m), which, for the 1 1/2-inch (40 mm) water meter, would be about 6 to 10 valves.

The 1 1/2-inch (40 mm) water meter appears to be the most efficient at this early examination. However, if you have a watering window requirement that forces you to operate more than one valve at a time (or larger valves), you may need the next size meter size up, or a 2-inch (50 mm) with a maximum flow of 120 gpm (454 l/m).

What are the other system requirements for your source?

Other system requirements relate to limitations of the remote control valves, mainline pipe, and backflow device.

The 1 1/2-inch (40 mm) water meter allows a maximum flow of 75 gpm (283 l/m), and a 1 1/2-inch (40 mm) valve allows for 60 to 75 gpm (227 to 284 l/m), which is efficient with this meter size. This would require a 2-inch (50 mm) service line to the water meter to supply the required flow completely.

At the velocity of 5 fps (1.52 m/s), a mainline of 2 1/2 inches (63 mm) would provide the proper flow. However, in the case of a sports field, expect longer runs of mainline – thus more likely requiring the next size up, or 3 inches (76 mm) for much of the project. A 1 1/2-inch (40 mm) backflow would allow for the maximum flow.