Abstract: A pressure relief valve comprises a poppet member that is biased toward and sealingly engages a slidable tubular valve seat having unrestrained axial rotation and a central relief flow passage. When the system pressure reaches a threshold pressure the valve seat and poppet are both axially displaced such that at the moment that the poppet is unseated from the valve seat, the valve seat is in motion. The motion of the valve seat when the poppet is unseating or reseating allows the valve seat to comply with any eccentricities of the poppet to achieve uniform seat stresses and low leakage rates as well as acceptable flow rates and low hysteresis.