AFT Blog

As tech support engineers, we sometimes receive questions from users confused about what control valve characteristic curve (inherent or installed) they are inputting into AFT Fathom, AFT Arrow, or AFT Impulse. The inherent control valve characteristic curve plots the valve open percent versus the percent of maximum Cv. This curve is true regardless of the system effects on the valve. The installed control valve characteristic curve plots the valve open percent versus the flow through the valve, and this plot is dependent on the conditions specific to the system. For example, if the control valve flow setpoint is fixed at 250...

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...