Understanding Irrigation Calculations
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Understanding Irrigation Calculations

Mar 03, 2023
Video Length:  1:12:16
Presented By:  Jake Lott

If you've done any irrigation design without the help of software, you're familiar with the staggering amount of effort and calculations required for sizing and otherwise configuring your system. Even when you're using tools developed specifically to help with these calculations, it's important to understand the calculations themselves – what to look for, how to read equipment performance charts, and how to make changes when something fails. 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.

Webinar Contents:

Note: The following catalog of content covered in this webinar is time stamped to allow you to follow along or skip to sections of the video that are relevant to your questions. You can also search for content on this page using the FIND command in your browser (CTRL + F in Windows, Command + F in Mac OS.)


  • Intro/TOC
  • General Concepts
    • How Pipe Sizing Works (simplified)
  • Starting a Design – Things to Remember
    • Source
    • Pipe
    • Equipment/Site/Client-Dictated Conditions
  • Dealing With Pressure & Flow
    • What to Account For & Where to Find It
    • How to Read It
  • Live Demonstration of Different Scenarios



0:00 – 3:02: Intro/TOC

3:03 – 4:02: General Concepts

How water works (3:03)


How Pipe Sizing Works (simplified) (4:03)

  • Speed the water up
    • More pressure loss
      • Smaller pipe sizes
    • Slow the water down
      • Less pressure loss
        • Larger pipe sizes

4:03 – 16:10: Starting a Design – Things to Remember

Source (4:03)

  • Source comes into play when sizing the mainline.
  • Available pressure and flow
  • Determining the right numbers
  • Did you leave enough buffer?
    • What is your residual?
    • What should be your residual?


Irrigation F/X power user tips:

  • Set water source as "Custom."
  • Zero out your flow and pressure.
  • Size mainline to get exact demands of what the system will need to operate.



Pipe (6:16)

  • Charts correlate to sizing laterals and mainline.
  • Velocity is the only variable to adjust since station flow is fixed.
  • I.D. is very important in the next step.


Equipment/Site/Client-Dictated Conditions (9:43)

Equipment affects working pressure, zone sizes, watering ties, etc.

  • RCVs, drip kit valves
  • Backflows
  • Water meters
  • Master valves
  • All emission devices


Sizing a system (11:55)

  • Size farthest head to valve, then move to POC.
  • Figure total friction loss.


16:11 – 20:07: Dealing With Pressure & Flow

What to Account For & Where to Find It (16:11)

  • Design pressure and emission performance data
    • When adding equipment to a project
  • Mainline and lateral line data
    • Set classes and sizes within Pipe Data
    • Size Lateral / Size Mainline dialog boxes
  • Pressure and flow available
    • Source Data dialog box
    • Critical Analysis (cross-check result)


How to Read It (17:55)

Final cross-checks (17:55)

  • Ensure positive residual flow and pressure
  • Have ability to see which station is the Critical Station


Tools to help (19:28):

  • Edit Equipment
  • Locate Valve
  • New Flow Zone
  • Valve Schedule
  • Mainline Profile
  • Schematic Irrigation
  • Delete Station
  • Boundary
  • Uniformity

20:08 – end: Live Demonstration of Different Scenarios

Note: We use the Hazen-Williams formula to calculate pressure loss.


See our Lateral & Mainline Pipe Sizing: How to Decipher & Test the Results documentation page for more information about how our pipe sizing function works and how to test the results. (21:03)


Setting up test cases (22:47)


Working with pipe caps (24:50)


Flow zones (26:09)


Error checking the system design (34:29)


Sizing lateral pipes zone by zone and toggling the settings (35:49)


Pressure variation (39:46)


Accounting for elevation on the site (41:34)


Accounting for loss through the valve (42:03)


The importance of running a Valve Schedule (43:42)


The importance of calling out your valves (44:48)


Checking the Source Data (46:30)


Sizing the mainline (48:57)


Sizing all valves vs. sizing one at a time when sizing the mainline (49:36)


What to do if you see the message "Pressure available at the point of connection has been exceeded" when sizing the mainline (51:39)


For help on what to do if you see this error message, see our Knowledge Base article on troubleshooting the issue.


Reading the Critical Analysis (53:05)


Finding a particular valve using our Locate Valve tool (53:53)


Placing a booster pump to raise the pressure (55:17)


Sloped sites (58:16)


Using Highlight Station to locate a valve and connected equipment (59:33)


Using our Mainline Profile tool to place an elevation profile of the mainline in the drawing (1:00:32)


Pressure loss through drip control kits (1:04:42)


Running an analysis from the Equipment Info dialog box (Edit Equipment tool) (1:05:46)

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