The two-way valve (a three-way valve may also be used) is installed in 

heating and cooling systems with a closed water circuit (e.g. central heating

systems, fan coil units, chilled ceilings or fan convectors) and serves the flow

volume and temperature control in combination with actuators and

thermostats.When used as a three-way valve, it is for mixing or distributing 

the volume flows in bivalent heating systems or hot water storage cylinders, 

for instance in solar or heat pump installations.