Three Port Motorised Valves
A three-port motorised valve can be used to MIX, in varying proportions, two flows of different temperatures while maintaining a constant rate of flow in the common outlet port.
A three-port valve with two inlet flows and one common outlet flow is defined as a mixing valve, and so provides a variable temperature outlet at a constant flow rate.
The diagram below shows a Mixing Valve with some typical water temperatures. A Mixing Valve is used normally for radiator circuits.
A 3-port valve may also be used to DIVERT a common flow in varying proportions. The valve will have one inlet and two outlets and provides a constant temperature and variable flow rate.
The diagram below shows a Diverting Valve with some typical water flow rates and temperatures. A Diverting Valve is used normally for circuits with convective heat transfer such as; heat exchangers, primary coil in indirect cylinder, heater battery, cooling coil.
It should be noted that it is the mode of flow within the valve and not in the system that determines whether a 3-port valve is a MIXER or DIVERTER.
The 3-port valve in the diagram below is a MIXING VALVE since it has two inlet flows and one common outlet flow.
The 3-port valve in the diagram below is a DIVERTING VALVE since it has one inlet and two outlets.
Some manufacturers only make a MIXING valve, so for a DIVERTING mode of operation such as a heater battery the valve may be positioned in the return pipe as shown below.
In the above diagrams the pump position is important since the system will not operate properly if the pump is not in the correct part of the circuit. It is possible to place the pump in the return pipes and some manufacturers prefer this due to the way that the 3-port valves are constructed.