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.
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.
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!
