Fluid pressure occurs in one of two situations:an open condition, called "open channel flow", e.g. the ocean, a swimming pool, or the atmosphere.a closed condition, called "closed conduit", e.g. a water line or gas line.hydrostatic pressure.Closed bodies of fluid are either "static", when the fluid is not moving, or "dynamic", when the fluid can move as in either a pipe or by compressing an air gap in a closed container. The pressure in closed conditions conforms with the principles of fluid dynamics.