The device and principle of operation of a thermostatic mixer

As an example to illustrate the principle of operation of a thermostatic mixer, a standard product with mechanical control is considered. The function of maintaining a constant water temperature in the mixer is performed by a thermostatic cartridge, which converts temperature changes into mechanical movement. Structurally, the thermostatic cartridge consists of:

-Case
-Perforated metal cylinder
-Plastic cylinder
-Sensitive temperature sensor (valve)
-In some models, a safety mechanism may also be installed that prevents accidental adjustment of the mixer settings (relevant if the device is used by children).

The temperature sensor consists of a brass or copper rod (stem) and a piston ampoule with an expanding material, sealed with a membrane. The filler is usually a combination of different types of wax. In some models, bimetallic plates can also be used instead of wax or paraffin. When heated, the contents of the ampoule expand and press on the membrane. The movement is transmitted through a plug to the stem, which shifts the valve, thereby reducing the supply of hot water and increasing the inflow of cold water. When the temperature of the outgoing water is below the set values, the paraffin in the ampoule compresses and the stem shifts the valve in the opposite direction under the action of a spring. This returns the temperature of the mixed flow to pre-set limits.

The use of thermostatic mixers allows:

-to reduce the total water consumption and the time to adjust the temperature, which increase during the temperature adjustment of the water.

-to significantly reduce (up to 40%) the consumption of thermal energy spent on heating water by regulating the temperature of the mixed water and automatically maintaining it at a set level. This is especially relevant for water supply systems where a gas boiler or an electric instantaneous water heater is the main component.
-to eliminate the likelihood of burns due to temperature and pressure fluctuations in the hot water system, as well as due to accidental switching on of hot water.
The main disadvantage of thermostatic mixers is the higher price compared to conventional mixers. In addition, thermostatic mixers are more sensitive to water quality due to additional moving elements, on the surfaces of which iron oxide deposits can form.

The type of control of thermostatic mixers can be divided into the following two types:

1. Mechanical mixers controlled by a handle, valve or lever.

2. Electronic mixers are more technically sophisticated models that run on batteries or mains power. They are equipped with electronic temperature and pressure sensors that automatically respond to the water flow and display the corresponding values ​​on the screen. Such devices can have buttons, a remote control or touch-sensitive control. Advanced models are often compatible with “smart home” systems. The use of such devices in the home is unnecessary in most cases. They are mainly used in the water supply of medical institutions, swimming pools, saunas, public toilets and catering establishments.

There are different models depending on the purpose:

-Shower mixers – characteristic is the absence of a spout and the “tub / shower” switching mode (only a shower hose can be connected to such devices).
-Bath mixer – with a non-rotating short spout, has a “tub/shower” switching mode and allows you to connect a shower hose.

-Universal mixer – with a long rotating spout and the ability to switch between “tub/shower” mode and connect a shower hose.

-Wash basin mixer – characterized by compact size, fixed or rotating spout.

-Kitchen mixer – with a higher, fixed or rotating spout.

In addition, thermostatic mixtures are classified depending on the material from which the body of the device is made:

1. Copper, bronze or brass mixtures – are characterized by high strength and durability, even in conditions of increased temperatures and pressures. Disadvantages are the comparatively high purchase and repair price. In brass models, errors in water supply regulation are more common.

2. Aluminum mixtures – work stably with temperature fluctuations, but are less resistant to vibration.

3. Ceramic mixtures – the selection criterion is usually the attractive appearance. Disadvantages are low abrasion resistance and susceptibility to mechanical stress.

4. Silumin and plastic mixtures – the cheapest models, but have the shortest service life.

The materials from which the external and internal parts of the devices are made must have the approval of the relevant authorities for use in drinking water systems. In particular, the temperature of the external surface of the control organs at the handle locations should not exceed 45°C, and all visible surfaces of the sanitary fittings must be made of corrosion-resistant materials or have a corrosion-resistant protective and decorative coating. Cracks, scratches, dents and other defects are also not allowed.

Recommendations for selection, installation and use

Installation of thermostatic mixers can be carried out on the wall, countertop or sanitary object, either by open installation, in which only the controls and spout are visible, and all internal parts are hidden by panels and trim, or by closed installation.

In general, the installation of this type of mixers differs little from the installation of conventional models. Most installation errors arise due to improper connections, which are due to the fact that models of European manufacture are designed for standard European water supply connections (left – hot water, right – cold water). Such products should not be installed in houses where water is supplied according to a different scheme, without making prior adjustments to the water supply system. The easiest way is to swap the connecting hoses and swap the hot and cold water spouts, however, in some cases it may be necessary to rebuild the water installation in the immediate vicinity of the mounted faucet. There are two options here: if the supply pipes are laid openly, you can use hoses and swap the outlets for hot and cold water. If the pipes are hidden in the wall, there is no way around adapting the installation of the water pipes accordingly.

For electronic mixers that run on electricity, a connection to the power grid is also required. This can be done either in the classic way by connecting the mixer directly to a socket, or through a transformer that reduces the voltage to the technical requirements of the specific device.

Otherwise, the installation is carried out in the following order:

1. The hot and cold water supply on the riser is shut off.

2. If there is an existing mixer, it is dismantled.

3. Eccentric plates are attached to the pipes to adapt them to the new device.

4. The installation of gaskets and decorative elements is carried out.

5. The thermostatic mixer is installed and fixed.

6. The attachments are mounted.

7. The water supply is restored and the functionality of the installed device is checked.

8. The temperature of the water coming from the thermostatic mixer is calibrated. To do this, remove the protective cover of the device, turn on the water and set the required temperature by turning the valve, guided by the values ​​of a conventional thermometer.

For the device to work correctly, the water pressure in the pipe should be between 1 and 5 bar, with the maximum permissible value being

8 bar. The difference between the pressure of cold and hot water should not exceed 10%. If this value is higher (or if the network pressure exceeds 5 bar), an additional installation of a pressure reducer is required.

Since thermostatic mixers are quite sensitive to the quality of the incoming water, the water supply system should be equipped with check valves and deep cleaning filters (recommended mesh size: no more than 315 microns). This, on the one hand, protects the structure from dirt and other deposits, and on the other hand, even prevents potential backflows between the hot and cold water pipes. These fittings do not need to be installed only if they are already integrated into the mixer unit.

To extend the life of the thermostatic mixer, it is recommended to carry out regular diagnostics and filter replacement (if necessary). During maintenance work, the shut-off valve should be closed, and according to the instructions, the mixer should be disassembled, cleaned and reassembled. In addition, it should be avoided to use the mixer during repair work on the water supply system in the building. Such work can lead to hydraulic shock, which can damage the device.

Summary

Thanks to their properties, thermostatic mixers are particularly popular and in demand, especially in apartment buildings where pressure fluctuations in the water supply system may occur. The design, which avoids burns when in contact with water or housing, makes this type of product suitable even for buildings and rooms where children and the elderly use the hot water system.