A mixing valve is a component of plumbing fixtures that allows for the regulation of central heating by mixing the heating medium (hot water drawn from the heat source supply, e.g., boiler) with the return from the heating system (i.e., cooled water returning from the system where it has released its heat through radiators or underfloor heating). The mixing valve thus enables the regulation of the temperature of the heating medium by mixing water.
This allows for the blending of both factors and thus achieving the most favorable temperature for us on both sides of the central heating system (i.e., on the heat source side - e.g., boiler or fireplace - and on the receiving installation side, i.e., our central heating).
✅ Mixing valves - mixers - usually come in two variants - three-way valves and four-way valves. Occasionally, valves with a greater number of ways also appear.
Which mixer to use? Three-way valve or four-way valve?
✅ This question is for HVAC designers, installers, or simply those familiar with the specific installation - as it depends specifically on the characteristics of the building and the heating concept in the particular property. It's not the case that, for example, a three-way valve has an advantage over a four-way valve or vice versa. Each of them offers a slightly different arrangement, and without inspecting the building or at least having knowledge of the basic assumptions of the given HVAC system, it's difficult to choose the appropriate mixer.
Among mixers, the three-way valve is by far the most popular - it's easiest to understand its operation using this example. Below is the diagram of the three-way valve and its operation:
The diagram depicts 3 paths - as found in the most common mixing valve, namely the 3-way valve.
Cold return is very harmful, especially for modern heating devices such as gas boilers. To limit it - or preferably eliminate it altogether - you can shorten the circuit by installing a low loss header at the appropriate location or by splitting the system into two using a plate heat exchanger.
✅ However, there is a cheaper and simpler method - you can do this by using mixing - that is, by installing a three-way or four-way valve. To avoid boiler corrosion, the valve should be set so that the water returning to the central heating boiler is not lower than 50-55°C (different data may vary around this threshold). Of course, when it comes to low-temperature systems, where the device operates at, for example, 45°C - such as with condensing boilers or heat pumps - the return temperature should be appropriately lower. The aim is to ensure that the temperature difference is not higher than 10°C, and preferably 5°C for more sensitive devices.
This mainly applies to steel boilers; old cast iron boilers do not require mixing, although they can be used for other reasons, such as gaining temperature control capabilities. However, cast iron boilers are increasingly rare devices.
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A three-way valve with an actuator is a more advanced version of a mixer - of course, this can also refer to a four-way valve with an actuator. Basic mixing valves usually have a manual control handle, but as we know, in modern central heating systems, we prefer automation for convenience. Therefore, a three-way valve enhanced with an actuator - will open and close automatically when needed, and we can control it from the room controller on the wall - or even from a smartphone.
A three-way valve with an actuator is often a key component in new HVAC (Heating, Ventilation, and Air Conditioning) systems or other industrial systems, including refrigeration. The main function of such an automated mixing valve is flow control - but in a way that allows for changing the flow direction or blocking it independently of manual control.
The three-way valve is equipped with three outlets, which can be used for conducting, mixing, or distributing the flow of the medium - we know that. ✅ The actuator - mounted on this mixer - is responsible for controlling the valve movement (opening/closing the flow) -> which enables its automatic or remote control. Thus, a three-way valve with an actuator is extremely useful in temperature control, fluid or gas flow regulation, and maintaining optimal conditions in various industrial processes and HVAC installations.
Mixing valves in pump groups play a primary role in ensuring optimal flow balance of fluids - in heating or cooling systems, to which so-called mixing-pump groups are applied. These are advanced devices controlling temperature, pressure, typically equipped with an integrated check valve to prevent water backflow.
✅ In pump groups, mixing valves are commonly used to regulate the temperature of underfloor heating or traditional heating systems (radiator-based), where maintaining a constant room temperature is required. Thanks to their adjustable feature - mixing hot and cold water in the right proportions, mixing valves allow for adapting the system to changing weather conditions and user needs, resulting in convenience, energy savings, and thermal comfort.
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