Minimally-Invasive-Surgery plays an important role as a modernized technique that offers patients more convenience compared to traditional surgical methods. By using trocars and specialized instruments through the small incisions, the injured area is diagnosed and treated effectively. Rinsing fluid is used for visualization and expansion in the operation area. Hardware-in-the-Loop simulator was implemented for the controller development of pressure expansion in the closed area by controlling the fluid flows. Methods of pressure estimation were proposed for the replacement of pressure sensor.