Resources 2025

Figure 1: Calculations|Tips2|Tips3Nov13|Tips4

Written by Ben Keiser | Nov 26, 2013 5:00:00 AM

AFT Fathom can EASILY size valves AND orifice plates with a SINGLE Control Valve junction!  There is no need to perform strenuous hand calculations to determine a valve Cv or an orifice diameter.  Just specify the system boundary conditions, pipe input properties, and the desired flow rate (or pressure) and AFT Fathom will calculate the Cv, K factor, and equivalent orifice diameter/area for you all at once!

Figure 1 illustrates a control valve junction at the location of a valve or an orifice plate.  For known flow, use a Flow Control Valve (FCV).  For known upstream pressure, use a Pressure Sustaining Valve (PSV).  Or use a Pressure Reducing Valve (PRV) for a known downstream pressure.

Figure 1: Calculate Cv, K factor, and equivalent orifice size based on known flow of 500 GPM.




After specifying the input and running the model, the Cv, K factor, and equivalent orifice size (based upon a discharge coefficient of 0.6) will be displayed in the Valve Summary tab of the Output window.  The results based on a known flow rate of 500 GPM are shown in Figure 2.

Figure 2: Resulting Cv, K factor, and equivalent orifice size using Flow Control Valve.




Finally, to verify AFT Fathom’s ability to size a valve or an orifice plate with a Control Valve junction, build identical systems on the same Workspace using the feature ( to read the Duplicate Special feature Tips and Tricks blog post).  Then, morph the duplicated Control Valves into a valve and orifice plate by holding the Control key down and dragging a valve and an orifice junction directly on top of the existing Control Valve junctions.  Figure 3 shows the result of the original Control Valve system that was duplicated twice with , and then the duplicated Control Valves were morphed to a regular valve and orifice junction.

Figure 3: Select the top system with FCV J2 & Duplicate Special twice. Then morph the FCV in the middle system to a valve and the bottom system to an orifice.




Once the resulting Cv or K factor is specified for the valve, and the equivalent orifice diameter with a discharge coefficient of 0.6 is specified for the orifice, the final results in Figure 4 show that the valve and orifice plate were sized correctly.  Notice how the resulting flow rates, valve Cv’s, K factors, and orifice sizes are the same!

Figure 4: Valve J12 and Orifice J22 have been sized correctly based on a Flow Control Valve requirement of 500 GPM.