In modern heating systems, a three-way valve is used quite often, since it is a means of quality control of the coolant - by temperature, and not by flow. After all, supplying optimally heated water to radiators is the best way to save energy.
Thermo-mixing cranes also have other useful functions, which you will learn about in this article. But first, it’s worth considering how the three-way valve works, and also to understand its internal structure.
Varieties of 3-way valves
All thermostatic three-way valves for heating are divided into 3 types according to the device and the principle of operation:
- mixing;
- separation;
- switching.
The purpose of each of the 3 varieties can be judged by the name. The first type of valve mixes two coolant flows with different temperatures, the second separates, the third is engaged in switching water between 2 lines. Recognizing them externally is not difficult, usually the principle of operation is depicted on the case in the form of a drawing. Here's what a three-way mixing valve looks like:
A similar designation is on the separation element. As for the switching cranes, there may not be any images on their case, but there are significant external differences in shape.
By mixing or separating the streams, the optimum temperature of the coolant supplied to the radiators of the heating system or the contours of the warm floor is achieved. Switching is used in gas double-circuit boilers, when the heated water must be sent alternately to different heat exchangers.
Device and principle of operation
To understand what it consists of and how a three-way thermomixing crane of the most common saddle type works, you should study the diagram below. Inside the brass body with three nozzles, 3 chambers are arranged by casting, the passages between which are blocked by poppet valves. They are fixed on one axis - the rod emerging from the body on the fourth side.
The principle of operation is as follows: when you press the stem, the passage for one flow will begin to open and gradually be closed for the other, as a result of which water of the required temperature will be obtained in the mixing chamber of the valve. She leaves the brass case of the element through the third pipe. The force of pressing the rod is controlled by a thermal head with an external temperature sensor installed in accordance with the scheme.
The whole process is worth explaining in more detail:
- Imagine that insufficiently warmed coolant comes from the side of hot water. Then the mechanism passes it on, and the third pipe is closed. The remote sensor is filled with a thermosensitive fluid and is connected via a capillary tube to a reservoir (bellows) inside the thermal head.
- When the sensor heats up, this fluid expands, its volume in the tube and bellows increases, as a result, the latter begins to press on the stem of the three-way valve. The moment of pressing is determined by the adjustment on the scale of the thermostatic head, adjusted to the desired temperature.
- After that, cold from the third nozzle is mixed with the stream of heated water and the temperature of the water at the outlet of the thermal valve remains unchanged, although heating of the coolant at the inlet continues.
- If the incoming water continues to heat above normal, then to maintain the set temperature at the outlet, the thermostatic valve can completely block the inlet and open the lateral duct. In this case, the rod lowers to its lowest position.
- As soon as the sensor marks the coolant cooling, the head slightly releases the stem, the valve seat opens on the hot side and mixing of heated water begins.
The method of adjusting a three-way valve with a thermostatic head with a sensor is the most popular, because it is quite accurate and simple, and does not require electricity.
Use of drives
In addition to the thermostatic head, the valve can be controlled in other ways. The first one is manual, when the depth of the rod is determined by the rotation of the handle outside the housing. Not the best option and is suitable only if the temperature of the water entering the nozzles is unchanged. Another option is control by means of a servo- and electric drive, receiving commands from the controller. To work with different actuators, another type of valve is used - rotary, whose device is shown in the figure:
There is a certain resemblance to a ball valve, only the working rotary element has a different hole shape in order to let the coolant pass in two directions at once. The principle of operation is simple: the axis is rotated by the required angle, rotated by the drive. The latter is controlled by a controller receiving pulses from one or more sensors. Typically, valve actuators are installed in complex or automated weather-controlled heating systems.
Schemes for connecting the valve to the heating system
When there is an understanding of what a three-way valve is and what its work is, you can consider various connection schemes, depending on the purpose and role of the element in heating the house. The installation of a 3-way heat mixing valve is carried out in 4 cases:
- To protect the solid fuel boiler from the effects of condensate and temperature shock after sudden blackouts.
- The coolant in the underfloor heating circuits must be heated to 45 ° C, the temperature is maintained by a mixing unit with a three-way valve.
- To maintain the required water temperature in different branches of the system.
- When you need to connect an indirect heating boiler to a single-circuit gas boiler.
In order to protect the solid fuel thermal unit from condensation, it is impossible to allow the supply of cooled water to the boiler tank from the radiator network during its heating. To do this, use the following boiler connection diagram with a bypass and a three-way mixing valve:
In a system of underfloor heating, this element performs the same functions. The circulation pump drives the coolant along the heating circuits until it starts to cool. As soon as this happens, the sensor and the thermal head will work, after which the three-way valve will add hot water coming from the boiler to the closed circuit. How to do the installation of the collector of underfloor heating, pump and valve correctly with your own hands is shown in the diagram:
The next example of the use and connection of this important part is the connection of a solid fuel heat generator and a buffer tank with a heat accumulator. To warm it up quickly enough, the temperature of the supplied coolant should be from 70 to 85 ° C, which is not needed at all in the radiator heating system. The three-way valve installed behind the tank together with a separate circulation pump helps to lower it.
Important. When installing the mixing valve, remember that the pump should be located on the side where the always-open branch pipe of the three-way valve is located.
The complex heating system of a large cottage can have many consumers connected by means of a hydraulic boom and a distribution manifold. Moreover, in each of the circuits it is necessary to supply a coolant with a different temperature. The highest boiler is needed for indirect heating, so there is no control valves on the piping to it.Other consumers need a cooler coolant, and therefore they are connected through three-way valves.
In the scheme with an indirect heating boiler and a single-circuit gas boiler, one also cannot do without a 3-way valve. The task of the element is to switch the flow of coolant to the coil of the hot water boiler on the command of the controller (the electric drive is triggered).
Budget items with fixed water temperature
In simple heating systems of country houses that receive thermal energy from a TT-boiler, it is allowed to put a three-way valve of a simplified type, acting independently. To work, he does not need a thermal head with a temperature sensor, and the rod is not there. The control thermostatic element is installed inside the housing and configured for a specific outlet water temperature, for example, 60 or 50 ° C (indicated on the housing).
A heat mixing valve of this type always maintains a fixed temperature for the coolant at the outlet; this setting cannot be changed. This gives rise to a plus and minus in the use of such reinforcement:
- The advantage is a lower price than the cost of a thermal head assembly. The difference is significant - about 30%.
- The disadvantage is that it is not possible to regulate the heating of the outlet coolant. When an element from the factory is set to 55 ° C, it will always supply water with this temperature ± 2 ° C.
Tip. Before buying a valve of simplified design, carefully read the technical documentation for a solid fuel boiler, it often indicates the minimum temperature of the return coolant. More information on the use of mixing valves can be found in a separate publication.
Conclusion
The thermostatic three-way valve is a very useful part of the heating system of a private house, which allows you to effectively use the heated coolant, and therefore, save fuel. In addition, this simple part plays the role of a safety element for solid fuel boilers and allows them to extend their service life. On the other hand, you should not put the valve unnecessarily and anywhere, always consult a specialist in this field.