PASS/HYDROSYSTEM uses the most advanced models/algorithms and libraries for all level of simulation (both proprietary and from the most famous researchers/ developers from all over the world).

This includes minor loss correlations by Idelchik, Miller, Ito; multiphase flow models by Chisholm, Friedel; drift-flux model, mechanistic models by Taitel, Barnea and Tulsa University Fluid Flow Project research group (with automatic closure relations selection); Settling slurry flow DHLLDV framework model by Delft University of Technology; Todini Global Gradient Algorithm for network solver; Powell derivative-free method for optimization; and many others.

The program also calculates very complex networks with flow rate control elements and helps users analyze those networks with visual topology analysis features.

Slug flow parameters (size, frequency, speed of slugs, etc.) for gas-liquid flow can be calculated and reported using TUFFP Unified model. Forces in elbows and flow-turns caused by gas-liquid slug flow are calculated and can be exported to PASS/START-PROF software for accounting them in piping stress analysis.

The PASS/ADD SURGE module implements the classical method of characteristics (MOC), using Riemann invariants and explicit numerical methods. It also considers possible cavitation during transitional flow, taking into account both, column separation effect and distributed vaporous cavitation. Unbalanced waterhammer induced forces on appropriate elements/nodes are calculated and transferred to PASS/START-PROF or other piping stress analysis programs.