The 4-Way Brass Mixing Valve 721 is used to mix supply water from a hydronic source with water returning from a system. It is designed for use in either closed loop or open loop hydronic systems. This 4-way valve has standard female NPT threads, as well as a maximum leak through rate of 1% to allow for water expansion during temperature changes. The valve position can be manually set using the handle. An Actuating Motor 741 can be used to automatically operate the valve.