FCV/PRV/PSV could not control pressure - Pressure was added to achieve control flow/pressure

A Critical Warning message in AFT Arrow

Full Message Text

Several variations are possible depending on which Valve Type is selected in the Control Valve Properties window:

  • FCV could not control flow at Junction X - Pressure was added to achieve control flow. See Valve Summary for more information.

  • PRV could not control pressure at Junction X - Reverse flow through valve, pressure was added to achieve control pressure. See Valve Summary for more information.

  • PSV could not control pressure at Junction X - Pressure was added to achieve control pressure. See Valve Summary for more information.

Explanation

The Control Valve could not control to it's set point and the Always Control (Never Fail) setting is enabled in the Control Valve Properties window. When the Always Control setting is enabled the program has the freedom to add pressure in order to make the solution mathematically possible. Then, the Valve Summary in the Output window gives more information about exactly how much pressure was added via the Pressure Drop Stagnation (dP) or Head Loss (dH) parameters. A negative dP or dH means it was a pressure rise. Normally you would see a positive dP or dH meaning it was a pressure loss. Furthermore, the Valve State output parameter in the Valve Summary will show "Failed - Had to add pressure".

Required Action

If you want the Control Valve to fail open or closed, then you can disable the Always Control setting in the Control Valve Properties window. Whether the valve fails open or closed is dictated by the Use Default Actions setting and related options below it.

If you intended for the Control Valve to actively control, then this critical warning identifies that the pressure is too low at this location and the Control Valve cannot meet the set point. This could indicate a mis-typed input or an operational problem. Double-check the inputs and corresponding units for the model including control valve settings, pumps, pipe sizes, and fluid properties. If there are no input typos, then there are many different conclusions that could be drawn, each one requiring a different solution approach that will depend on your unique system: undersized compressor, higher than expected junction losses or K Factors, higher than expected pipe friction, or pipe fouling changing the internal diameter/velocity.