An in-house simulation program was developed that can be utilized to predict flow characteristics such as pressure and velocities in any flow network system comprising multiple flow components, i.e., pipe, pump, heat exchanger, valves, etc. Although the code is intended for applications to network flow systems in a vehicle, it is written in a generalized manner to handle any possible network configuration of flow components. Therefore, it can easily function in various industrial applications. The network system where the flow is assumed to be one-dimensional is mathematically formulated by applying two conservation rules, mass and energy, to each flow component. These rules produce a set of non-linear equations. These non-linear equations are solved iteratively by adopting the Newton-Raphson scheme. This program has been tested in many different cases to demonstrate its validity and applicability. In this paper, two examples are introduced to show how the program can be used to find solutions in real engineering problems. Throughout the study, it was found that the code can most efficiently be used to verify a proposed design concept in an early design stage of the vehicle development cycle. The thermal analysis portion of the program will be dealt with in Part II of the paper.