Adjustable thermostatc and pressure balanced mixing valve - 85 degree to 150 degree setting range - 75 PSI maximum operating differential pressure - 20 PSI maximum recommended differential pressure - 200 degree maximum hot water inlet temperature - The 521 series three way thermostatic mixing valve is used in systems producing domestic hot water or in hydronic and radiant heating systems. It maintains the desired output temperature of the mixed water supplied at a constant set value compensating for both temperature and pressure fluctuations of the incoming hot and cold water.