Explain the closed loop control system for a flow through a pipe?

closed loop systems is contain the feedback concept and the feedback is the relation between the   input and output signals in our case it is the relation between the flow rate at start of pipe and the flow rate that comes out of it and there is control unit of our flow which calls valve which play the role of get the variance between input and output flow rate we can adjust it like we need to decrease or increase the flow and by knowing the differnce of the output flow rate from the input and if this rate is the desired one or not and adjust it by the valve which connected to the output flow rate measurment device whatever is it

A flow through pipe is continuously measured and compared with the desired value to get the error signal (error signal is a difference between actual and desired values). Based on this error signal, the controller gives a signal to actuate the valve to adjust the flow (increase (or) decrease depending on the value of error being positive (or) negative). This is called a closed loop control system