This paper presents an analysis of flashing and non-flashing water flows through a safety relief valve. A set of experiments has been carried out on the CROSBY safety valve and its model. The pressure distributions inside the valve, the inlet and outlet temperatures and the mass-flow rates (critical or otherwise) have been measured. The characteristics of the valve giving the mass-flow rate as a function of the square root of the pressure drop are given. The experimental results are compared with equilibrium and relaxation two-phase flow models. The non-equilibrium character of fast evaporation and its substantial influence on the two-phase flow behaviour are demonstrated.