Sizing the Mainline Pipe
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Sizing the Mainline Pipe


Before sizing the mainline pipe, it's always a good idea to verify the mainline piping using our Verify Mainline tool to ensure that all piping is connected to equipment.


Looking for information on sizing lateral pipe in your design? See our Sizing Lateral Lines documentation.

Size Mainline Pipe Overview

Open our Size Mainline Pipe tool:



F/X Irrigation ribbon, Size Mainline Pipe flyout


F/X Irrigation ribbon, Size Mainline Pipe flyout







Irrigation Piping toolbar


Irrigation Piping toolbar

F/X Irrigation menu


F/X Irrigation menu, Size Mainline Pipe option



or type MainLineSize in the Command line



If you only have one water source or point of connection (POC) in your drawing, the Mainline Size dialog box will open automatically.

If you have multiple sources or POCs, the cursor will turn into a pickbox and you'll be prompted to select a source. You'll then see the Mainline Size dialog box.

Mainline Size dialog box, overview

1. Single Valve Operating at a Time: Operating a single valve at a time is common for a smaller system. After one valve operates for a given time, it will close and the next valve in line will turn on.


2. Multiple Valves Operating at a Time: Operating multiple valves at a time could be necessary for achieving a particular watering window where you need to maximize the system. If you select this option, you'll need to enter a Maximum Mainline Flow in the field to the right. The current value indicated in that field will be the maximum allowed by the Point of Connection (POC) as established in the Source Data.

If you're using Multiple Valves Operating at a Time, enter a Maximum mainline flow that's realistic, and that will represent operating two or more of your common valves at one time. The larger the number entered will result in a larger mainline size. Just because you have a very large flow available does not necessitate an excessive, and thus excessively large, mainline.


3. Maximum mainline flow: For the Single Valve Operating at a Time option, this number will default to the flow of the valve with the highest flow rate in your drawing. For the Multiple Valves Operating at a Time option, this number defaults to the flow rate of your water source.



4. Velocity: This text displays the maximum velocity currently set in the Pipe Data. If you want, you can adjust that rate using the slider.



5. Calculated pipe size: These text fields will populate with the required size for Standard (non-looped) and Looped mainline in your system design.


6. Elevation data: Select one of these options to choose whether you want to calculate elevation differences between your source and your valves using elevation callouts you've placed using our Spot Elevation tool:

  • No elevations: Do not take elevation calculations into account when sizing the mainline.
  • Use Spot Elevations: If you choose this option, you'll want to place a Spot Elevation near the point of connection (POC), then place Spot Elevations to reflect the change in terrain as will occur on the site. Any valve will automatically look for the nearest spot elevation and assume it's at that elevation. For that reason, we recommend placing an adequate number of Spot Elevation callouts to allow the system to account properly for terrain changes.
  • Last value set: If an elevation has been applied manually to the selected valve using our Edit Equipment tool, select this option to apply that elevation value to the valve when calling it out.


7. Select Valves: If you want, you can size the mainline to only certain valves. You might use this feature if you have an extremely large system and only want to resize a portion of it.


8. New Flow Zone: This is an optional feature. Clicking this button will allow you to insert a Flow Zone to force control of the flow in certain areas of the mainline. See Flow Zones below.

When you click OK, the mainline in your drawing will size and a Critical Analysis dialog box will open. For more information, see our Critical Analysis documentation page.

Mainline Calculation Information

The mainline pipe sizing uses the Hazen-Williams formula to size the pipe. This formula calculates the inside diameter required and related pressure losses for given flows and lengths of pipe from data supplied by the flow in the pipe resulting from the valve requirements, the maximum velocity, and the roughness coefficient. The system is sized to account automatically for looped mainline conditions if they occur.

You can control all data and system requirements using our Pipe Data tool. For further information and instructions, see our Pipe Data page.

Looking for a way to cross-check how our mainline sizing works? See our Pipe Sizing: How to Decipher & Test the Results documentation.

Accounting for Future Demand

The mainline sizing is demand-based. Therefore, if you want to account for a possible future demand, you will still need to create the demand (and thus confirm the mainline can deliver that water).



To account for this future demand, you can add a cap for Future Use from the Auxiliary Equipment. Caps can stand in for any theoretical or future demand you specify.

For instructions on adding a cap for future use, see the Adding a Cap section of our Adding Auxiliary Equipment to a Project documentation page.

Sizing the Mainline Manually Using a Pipe Cap

If you have a specific diameter of mainline pipe in mind, you might want to size the mainline manually to achieve that diameter.


For example, you might have a 2-inch meter and the system is sizing for a 1.5-inch mainline coming out, but the client wants to see a 2-inch mainline coming from the meter.


Our Size Mainline tool is demand based. To size the mainline manually, you'll need to invent a demand that will force the mainline to have the diameter you want to use. You can achieve this goal by placing a pipe cap and connecting it to your water source. Here's how.

This method is also the easiest way to validate our software's pipe sizing calculations.

Sizing a Looped Mainline

If you need to size a system that includes loops in the mainline, you'll need to take a few factors into consideration:


• Size for Multiple Valves

There's no reason to size a looped mainline with just one valve running at a time. Instead, you should size looped mainline for Multiple valves operating at a time.


This setting will allow you to set a Maximum mainline flow to size for, which is a crucial consideration when sizing a looped mainline.

With a looped mainline, the Multiple Valves option will size all looped pipe at half the calculated flow, while the flow around a loop will vary if you use the Single Valve option.

Sizing for multiple valves


• Check for Errors

It's always a good idea to error check before sizing the mainline. With a looped system, it's especially important to check for errors to ensure that:

  • The mainline is actually looped.
  • The system does not have any piping errors.


You can delete a few segments of your looped mainline and use our Highlight Station tool to confirm that all is good.

Note that our Verify Mainline tool – usually another essential error-checking step – is not as effective in a looped system as it is in a standard system.



• Practice by Setting Up a Test Case

If you haven't sized a looped mainline before, we recommend that you first set up a simple test case, with just a POC to a looped mainline with a pipe cap placed on it. Caps are available from our library of auxiliary equipment.


Try sizing the mainline in this simple system to familiarize yourself with the nuances of our sizing. In this manner, you’ll see that sizes not in the list are absolutely changed out when you resize. As mentioned above, our Verify Mainline tool is not as effective with a looped mainline as it is in a Standard layout. A looped mainline most definitely puts more pressure on the designer to make sure the piping is still connected correctly.

Using Multiple Pipe Classes

Our Pipe Data tool allows you to specify up to 9 classes of lateral pipe and 6 classes of mainline in each of your projects.






As long as you meet a few specific criteria in setting up your pipe classes, the system will automatically assign each of your classes to the correct size of lateral or mainline pipe once you size your pipe.


More information about using multiple pipe classes

Classes assigned to pipe

Sizing Error Resolution


If an inadequacy occurs in the system when you size the mainline, you'll see an error message.


The most common error type is a lack of pressure, which triggers a message that Pressure available at the POC has been exceeded.

Pressure available at the POC has been exceeded error



If you click Yes, the system will resize and automatically reduce the velocity down in small units until it reaches 3.25fps (0.99m/s).




Unable to size the mainline error

If the system is unable to size with this lower velocity, you'll see another error message: Unable to size the mainline. Highlighted valves have pressure or flow requirements that exceed that available at the POC.




Click OK.



A Critical Analysis dialog box will appear, and valves that could not be sized will be highlighted in your drawing.

Critical Analysis dialog box




You'll now have several options for actions you can take to deal with certain valves that will not size:



Option 1: Reduce the Velocity in the Lateral Line and Mainline Sizing

If your negative Residual Pressure Available is a small number (-3.0 psi / -0.21 bar or less), you could consider going to the Pipe Data and lowering the Maximum Flow Velocity in the lateral line piping, as well as resizing the lateral line valves that were having a problem. The default for Maximum Flow Velocity is 5.0 fps (1.5m/s). Depending on the pressure you need to mitigate, lower it to a level of about 3.75 fps (1.14 m/s) and resize the problem valves. Next, resize the mainline – most likely with a comparable lower velocity in the Pipe Data.



Option 2: Use Different Heads at the Problem Valves

The problem may be originating from one or two valves with heads that require a high operating pressure. You might delete those heads on the problem valve(s) and redo the system with a different head that has a lower operating pressure. Note, however, that this will usually necessitate heads with a shorter radius, meaning more heads will be required.



Option 3: Use a Different Design Pressure for the Problem Valve Heads

You could select the Edit Equipment option (see Review With Edit Equipment section below) and click one of the heads at the problem valve. Then click the Design Pressure button and attempt to simply reduce the design pressure required for that head to a lower amount. (The issue may be occurring because you have originally chosen a very high, somewhat over-optimistic design pressure when you first added the head to your project.)



Resize the problem valves to reflect this new lower pressure requirement.

Note: When you change the Design Pressure, the new radius amounts – resulting from resizing the system – will be changed, and the existing configuration may not be appropriate for this new lower pressure.



Option 4: Add a Booster Pump

If the pressure difference is fairly great, such as 10 psi (0.69 bar) or greater, adding a booster pump may be your only alternative. Because of the cost and power requirements, this is usually a last resort.

Review with the View Data/Edit Equipment Tool

The View Data / Edit Equipment tool is valuable for reviewing the requirements of a piece of irrigation equipment, such as a head or valve, or any given length of pipe.


Open this tool:


F/X Irriagtion ribbon, Edit Equipment button


F/X Irrigation ribbon, Edit Equipment button



Irrigation Piping toolbar


Irrigation Piping toolbar



or type EquipInfo in the Command line

Mainline Pipe Size Label Organization

When you size a mainline system using the Mainline Pipe Size tool, labels of the pipe size notations are automatically placed off to the side of pipes that are transitions from one size to another, and not on every single pipe length. Thus, the first and last pipe locations, or transitions, are the only pipes called out with a pipe size.



A few of the pipe labels that are automatically placed into the drawing may conflict with other labels, the piping, or some of the background drawing. You can easily move, delete, or add to these labels by using our Pipe Label tool.



Open Pipe Label:


F/X Irrigation ribbon, Pipe Label flyout


F/X Irrigation ribbon, Pipe Label flyout




Irrigation Piping toolbar



F/X Irrigation menu


F/X Irrigation menu, Pipe Label option



or type PipeLabelCleanup in the Command line

Flow Zones

Flow Zones allow you to set a limit on the flow in a certain area of the mainline in your design.

For further information and instructions, see our Flow Zones page.

Note that Flow Zones only limit flow – they don’t increase or decrease it. If you have a flow of 100 GPM downstream of an 80 GPM flow zone, for example, the zone can’t reduce the flow – it's already 100.

The mainline will size for the amount entered in the Maximum Mainline Flow box – in the example above, 208.81 gpm – but the Flow Zone areas will be forced to size for their given Flow Zone amounts.

Valve-in-Head (VIH) Rotors

Valve-in-head (VIH) rotors are generally piped with constantly pressurized pipe, which, by definition, is mainline. Although you'll use our Lateral Pipe tool when piping to and between VIH rotors, the system will recognize the valves in the heads and will treat the pipe as if it's mainline. When sizing this pipe, you should use our Size Mainline tool. See our VIH Rotors page for more information.

Deciphering & Testing the Results of Our Pipe Sizing Tools

Wondering how our pipe sizing tools calculate their results, or hesitant about the numbers that are generated when you size your pipes? We've created some pipe sizing tests that will help you interpret the sizing results and determine whether your pipes are being sized correctly.

Mainline Pipe Information

For general information about drawing mainline pipe, see our Mainline Piping page.

Related Webinars

  • Understanding Irrigation Calculations: Join us for a deep dive into exactly what our software is doing when sizing your irrigation design. We'll cover where losses occur in different types of equipment, which schedules are available to help you analyze your system, and how to make the proper adjustments for a successful final product. (1 hr 12 min)
  • Irrigation for Beginners: We'll show how to navigate through the Irrigation ribbon and build a familiarity with our conceptual-level tools. You'll also learn the basics of adding equipment to a project, placing, piping, sizing, and scheduling. (1 hr 45 min)
  • Getting Started with Irrigation F/X: Join us for this webinar to get going with the essential capabilities of Irrigation F/X. We'll show how to navigate through the Irrigation ribbon and build a familiarity with our conceptual-level tools. You'll also learn the basics of adding equipment to a project, placing, piping, sizing, and scheduling. (1 hr 8 min)
  • Understanding Pressure and Flow: Learn the differences between static and dynamic pressure, how specific equipment types affect that pressure, how flow affects pipe sizing, and what to consider when dealing with pressure issues both before and after installation. (1 hr 4 min)
  • Start to Finish Basics of Irrigation Design: This webinar will help give you an understanding of how to specify the proper equipment, talk about important concepts of irrigation design, and create a complete irrigation plan from start to finish. (1 hr 31 min)
  • Irrigation Tools – What You Need to Know: We'll show you the ins and outs of basic irrigation setup using our software. You'll also learn the essentials of placing equipment such as drip, sprays, and rotors. (1 hr 6 min)
  • Irrigation Tips & Tricks: We'll show you some advanced tools you may or may not know about. You'll also learn techniques and best practices that will help speed up your workflow. (1 hr 3 min)
  • Existing Irrigation: Learn the techniques, tools, and tricks you'll need to expand an existing system, including how to use a pipe cap to account for existing flow and add new valves to an existing mainline. (56 min)
  • Advanced Irrigation Troubleshooting: Learn to think like a Land F/X irrigation troubleshooter. We'll show you why your symbols don't match, why you would see the message "Error accessing equipment data" (and how to fix these issues, as well as tips on pressure losses and precip rates, pipe caps, system monitors, and flow zones. (1 hr 3 min)
  • Golf Course Irrigation: We'll demonstrate some of the great tools Irrigation F/X offers to help ensure proper mainline sizing and scheduling. We'll also discuss the use of using flow zones, shut-off valves, and valve-in-head rotors. (1 hr 4 min)


Issue: You can't size the mainline – general mainline sizing troubleshooting


Issue: The Critical Analysis is incorrect


Issue: You saw a message that your irrigation system doesn't have enough pressure


Question: Can I Use a 1 1/4-Inch mainline with a 1-Inch solenoid valve and an output to a 2-Inch lateral line in a 20.9 GPM zone?


Issue: "Unable to size system" error when sizing the mainline


Issue: You have a specific diameter in mind for your mainline, and you want to size the mainline manually


Issue: You need to run multiple (two or more) valves at a time


Issue: Error executing data request: data too long for column 'data_code' (when sizing the mainline)


Issue: The pressure loss for the master valve is not appearing in the Critical Analysis


Issue: 999 PSI pressure rate when sizing the mainline


Issue: Your pipe sizes are in the wrong measurement system – for example, you might be desgining in Imperial units (feet and inches) but the pipe sizes are in metric


Issue: You want to use custom linetypes for different pipe sizes


Issue: You're trying to size the mainline, and the the Recursing pipe process is taking an excessive amount of time


Issue: You used Spot Elevations when sizing your pipes, and the system is either using the wrong elevations, or you're not sure why it chose the elevations it did

Last modified on Tuesday, 06 June 2023 16:39
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