A long-life conductivity sensor system and method that is embeddable or immersible in a medium. Solid particles are prepared from a melt of the phenolic antioxidants are added to a dispersion comprising the solid particles of the compound in a mixture of an organic water-miscible solvent and water and the crystals obtained from the dispersion are separated. In preferred forms, the pressure reducing valve includes a valve insert housing a spring that, among other functions, serves as a reset valve to further reduce the space requirements and decreasing the cost and complexity of the valve assembly.