The aim of this work is to study the fluid hammer and related multiphase phenomena taking place in a confined environment, where pressurized liquid faces vacuum conditions after opening an isolation valve. This paper describes the experimental facility built for this purpose, the tests performed, and shows the comparison with the numerical results obtained with a transient one-dimensional software based upon conservation equations. Because the multiphase phenomena taking place in the liquid front moving along the pipe are complex and difficult to interpret, a graphical tool by means of diagrams was adapted by the authors to characterize the physical phenomena involved. Contrary to the classical water hammer analysis published in the literature so far, the diagrams allow a simultaneous study in time and space for each of the magnitudes involved in the evolution of the fluid hammer.