Subcooled water critical flow phenomena in a safety valve are investigated experimentally at various subcoolings between 10 and 125 K, and about 1 MPa of the inlet pressure with three different disk lifts, 1, 2, and 3 mm. The purpose of this experiment is to find the effects of subcooling and disk lift and to visualize flow patterns in a safety valve when the critical condition is established. All of the experiments show the critical characteristics such as constant throat pressure and constant flow rate when the back pressure is sufficiently decreased. Two correlations, critical pressure ratio and non-equilibrium factor, are developed by using the present experimental data represented in the form of non-dimensional disk lift, subcooling, and pressure. Critical pressure ratios and non-equilibrium factors are considerably affected by different subcoolings while the effect of disk lifts on them is relatively small. A non-equilibrium critical mass flow correlation for the safety valve is also developed based on Fauske's non-equilibrium model and the presented experimental data. The predictions of the correlation are within +/-11% of the experimental data.