The main objective of this chapter is to present a procedure that obtains a first approximation of the geometric physical limits of the Real Hydraulic Flow Path (RHFP) in the Rotor Shells (RS) of the PHIT. The complexity of studying these physical limits, between each half of the flow and the respective inner surface of the shells, must occur with minimal friction and turbulence (shocks) in a very short time, i.e., in the order of a tenth of a second. Even when using computational resources, the results can be far from representing real flows. To improve this, exhaustive laboratory studies on homologous models (which are geometrically similar, with the same specific rotation) should be conducted. Given these facts, the chapter will be limited to developing studies that allow us to graphically or analytically obtain the relationships between flow characteristics and the PHIT geometry, using the Principles of Mechanics applied to Hydrodynamics (Euler’s Equation) and coefficients, preferably dimensionless ones. Having done this, we will be able to develop and validate algorithms that will reproduce scale drawings of the PHIT RO, particularly the shells. These algorithms, and the respective software that will result from them, may be used to prepare the structural calculations, the respective Preliminary Project, and manufacture of models, which, via tests, will establish the Executive Project and the Manufacturing Project according to the contracts agreed upon by the parties involved.