Flow device systems for use in an HVAC system (“HVAC”) are described. The system may include a controller receiving sensor signals including differential pressure, valve commands, fan/pump speed, and fan/pump motor power signal from the HVAC. The controller transmits override valve commands for multiple valve positions of the valve and multiple speeds of the fan and pump. A characteristic curve may be determined from the signals provided from the HVAC and the measured flow rate at each valve position or fan/pump speed during transmission of the plurality of override valve commands for the valve positions of the valve and fan/pump speed for fan/pump operation frequencies. Virtual flow rate through the valve, fan or pump is determined using the characteristic curve. In addition, valve dynamic behavior is determined using valve stiction and valve stiction plus deadband. Valve commands are updated based on valve dynamic behavior and a valve characteristic curve.