PID control on Pinch Valve

[Khushwant Parihar]

Hey there I am trying to control the pinch valve using pid , The setup I have is like this 

I have a cylinder which is connect through a pipe and the pipe is pinch valve ( it's a rubber pipe) and then after that there is flow sensor . 

I want to control the user to specify the flow rate he want's and the pinch valve should open and close accordingly 

Here is my approach for trying that Now i don't know how to implement PID into it .

void run_tmc_stepper(int setflow)

{

flowsensorvalue = flow_sensor(); //this will give the value of flow sensor

   stepper_Y.setCurrentPosition(0);

  if(setflow>flowsensorvalue)

  {

    if(diff > 5 )

    {

      stepper_Y.runToNewPosition(-highincrease);

    }

    else if ( diff > 3 && diff <=5)

    {

      stepper_Y.runToNewPosition(-mediumincrease);

    }

    else if (diff <=3 )

    {

      stepper_Y.runToNewPosition(-lowincrease);

    }

    return run_tmc_stepper(setflow);

  }

  else if(setflow<flowsensorvalue)

  {

    diff= diff*(-1);

    

    if(diff > 5 )

    {

      stepper_Y.runToNewPosition(highincrease);

    }

    else if ( diff > 3 && diff <=5)

    {

      stepper_Y.runToNewPosition(mediumincrease);

    }

    else if (diff <=3 )

    {

      stepper_Y.runToNewPosition(lowincrease);

    }

    return run_tmc_stepper(setflow);

  }

  else if(setflow == flowsensorvalue)

  {

    return 0;

  }

}