So I was playing around with Fluid Pressure and Flow over on PHET animations and noticed something odd. When a fluid with high flow rate is going from a large pipe to a small pipe a lower density increases the pressure. And a higher density lowers the pressure in the narrow part of the pipe. My knowledge would say that the higher the density the higher the pressure with other variables constant. Was wondering if some one could let me know if this is a software issue or could point me in the right direction to read about this a bit more.