Critical Analysis

The Critical Analysis is a report, placed into your drawing, that provides the flow and pressure statistics of your irrigation system design. It contains the same information as shown in the Critical Analysis dialog box, which appears when you size the mainline. You can also generate a Critical Analysis manually.

Critical Analysis Overview

Generate a Critical Analysis manually:

 

F/X Irrigation ribbon, Critical Analysis flyout

 

 

Irrigation toolbar

 

 

Irrigation Manager toolbar

F/X Irrigation menu, Critical Analysis option

 

 

or type FX_CriticalAnalysis in the Command line

 

A Critical Analysis is created automatically when you size the mainline.

 

The Critical Analysis lists the point of connection (POC) number, the Flow Available, the Pressure Available, and a Design Analysis of the Maximum Station Flow, with the Residual (or leftover) Flow, the pressure loss to provide the Critical Station (most demanding valve), and the Residual (leftover) Pressure.

 

 

Here's an example Critical Analysis dialog box that appears after the sizing of the mainline:

 

 

The image below shows what the same Critical Analysis would look like when inserted in a drawing manually.

 

Placing several of these reports into your drawing for owner or agency review of your work can be an important aid in communicating your design parameters.

Understanding the Critical Analysis

Follow our steps to size the mainline.

 

 

Once you click OK to size the mainline, the system will size and you'll see a Critical Analysis dialog box.

 

 

1. Flow Available: The available flow at your water source or point of connection (POC), along with the given size. You can set your system's available flow using our Source Data tool.

 

2. Pressure Available: The available pressure at your water source based on the Static Pressure at Service setting in your Source Data, as well as additional factors that affect the source pressure.

 

3. Design Analysis: Compares the highest design flow in your system against what is available at your source.The Residual Flow Available is the remaining flow after demand.

 

4. Critical Station: The station in your system with the highest pressure and flow needs – often, but not always, the farthest station from the source. In this example, the Critical Station is Station 24, which requires a pressure of 51.64 PSI. The Critical Station sill be listed as long as your valves are called out properly.

 

5. Residual Pressure Available: The most important item in the Critical Analysis.

 

If your system has insufficient residual pressure, this item will appear as a negative number. If so, the system will not continue sizing the mainline. If you see a negative number as your Residual Pressure Available, you'll need to correct your design to allow your system to function and size without error.

 

The maximum flow should have been controlled with the Circuiting process, and should not have been exceeded if this process were completed correctly.

 

 

How the Critical Analysis Is (and Isn't) Calculated

Our software generates the Critical Analysis by applying the Hazen-Williams Formula to your system design, calculating from the farthest head back to the valve, then from the valve back to the source or POC.

 

The calculations in the Critical Analysis DO NOT work down from the pressure available – instead, they work up from the demands.

 

 

Additional Notes on the Critical Analysis

  • Need to investigate the Critical Station further, or do you simply see a problem station (valve) in your design? Use our Locate Valve tool to find that valve quickly.

 

  • Because the final Pressure Available is essentially a guess until the mainline is ultimately sized, exceeding this factor is a common source of problems with irrigation designs. Also, you'll need to account for the life of the project when designing your system. Factors such as wear and tear of pipe joints can cause a drop in pressure over time. An increase in local demand or a decrease in available municipal flow can also deprive your system of pressure in the future. We recommend having a Residual Pressure Available of about 5% of the Critical Station Pressure, which will account for potential pressure drops as well as pipe corrosion.

 

  • Remember: You can use our Schematic Irrigation tools to preview what your pressure demand and system requirements might be – before you design your system. We recommend saving yourself time and potential frustration by using Schematic Irrigation to determine your system's needs before beginning your design.

 

  • We recommend that the Critical Station have a residual pressure buffer of 5%, to account for potential pressure drops over time. Our software accounts for this buffer automatically.

The Valve Schedule

The Valve Schedule is the logical companion to the Critical Analysis, as it will show the flow and pressure at each station – including the Critical Station.

 

 

The image below shows an example Valve Schedule. All 26 stations from the drawing are shown. Note that the Critical Station, Station 24, has the highest required pressure at 51.6 PSI.

 

Related Webinars

  • 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)
  • 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)

Troubleshooting

Issue: Critical Analysis is wrong

 

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

Last modified on Thursday, 27 September 2018 10:14

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