Mixing valves are mainly used in heating installations. They are used for proportional mixing of the working medium returning from the installation, with the supply medium, or for mixing factors from two different sources. Thanks to them, it is possible to use single-function heating boilers also for heating of utility water. They can be manually controlled or equipped with an electric actuator - then they cooperate with such controllers as: switches, thermostats, programmable thermostats, control units, boiler or heat exchanger automatics. Four-way mixing valves additionally protect the solid fuel (coal, pellet, wood) boiler against the phenomenon known as: low-temperature corrosion.