Thermostatic valves are a common part of heating or cooling systems. They are used as temperature control - to protect against scalding and also to reduce the risk of damage to your boiler due to low-temperature corrosion. They will therefore save energy and your costs.
Their purpose is to maintain a constant temperature. Mixing hot and cold water so that the set water temperature is always ensured at the outlet. It is a three-way valve that does not need electricity to operate. Inside the valve there is a thermostatic cartridge as a control element. It works on the principle of thermal expansion of matter. In physics it is defined as a tendency of a solid body to change its dimensions responding to changes in temperature - thus the body size changes, while most substances expand when heated.
In the case of thermostatic valves, thermal expansion of material is used in a bimetallic element, where two metal strips of different coefficents are firmly coupled. When the temperature changes, a set change in dimensions occurs.
As the temperature rises, pressure is exerted on the plunger (pressure needle) in the thermostatic valve and the valve closes. Conversely, as the temperature drops, the size of the body decreases, the valve plunger loosens and it opens again.
Thermostatic valves vary in size, thread type, connection dimensions, flow or cartridge replaceability. These wear out over time and need to be replaced; you can get the thermostatic cartridges for fixed temperature valves as a commonly available spare part.
As a rule, the cartridges cannot be replaced in brass valves with adjustable temperature. Instead, exchange kits are supplied. The entire valve core can be refurbished with the kit.
We recommend focusing on the temperature range and the opening temperature - the opening temperature is the one at which the valve begins to open. However, it is fully open only at a temperature 10 °C higher.
We also distinguish thermostatic valves according to use. Cast iron / brass with a fixed mixing temperature for heating or for filling the boiler with hot water help to protect against low-temperature corrosion. There are also adjustable temperature brass valves for domestic hot water, where the valves are used mainly as protection against scalding. Last but not least, there are valves with increased flow, which are used for underfloor heating.
Since every rule has an exception, you can also get a thermostatic filling valve VTC422, which is used as a protection of a boiler for solid fuels, but has an adjustable temperature.
As described earlier thermostatic valves are also divided into fixed and adjustable categories. Fixed are also called filling - they are used to fill boilers or storage tanks with hot water. Thermostatic cartridge can be easily replaced with a cartridge with a different opening temperature.
There are two reasons for filling the boiler with hot water. The first is to maintain the efficiency of the boiler, the second reason is protection against low-temperature corrosion.
Low temperature corrosion is caused by the fact that some components of the flue gas with water vapor, which is present in the flue gas, form acids at a certain temperature. Vapors of these acids then condense when the boiler exchanger surfaces cool to a temperature lower than their dew point. This creates an aggressive acid condensate. It attacks the boiler material, which quickly corrodes.
Another accompanying phenomenon of operation of the boiler's heat exchange surfaces below the flue gases dew point is sticking of fly ash and formation of deposits - tarring. Such a situation can clog the flow cross-section for flue gases, which significantly reduces the life of your boiler.
The thermostatic valve keeps the walls of the boiler at the required higher temperature by mixing cold water from the boiler inlet with hot water from the boiler outlet.
Low temperature corrosion is a problem in the vast majority of boilers. Depending on several quantities (mainly fuel and boiler design), boilers require a minimum return temperature for rated output. In the case of sulfur-free fuels, the range is between 40 and 70 °C.
A load unit with a pump is a system consisting of a thermostatic valve, a pump and thermometers. It is used to ensure and maintain a high and stable return water temperature to the boiler. This parameter contributes to protection against low-temperature corrosion.
The advantage of the load unit over the thermostatic valve itself is that you get an overview of the temperatures on the individual branches. As a circulating pump is included, it is not necessary to purchase another pump separately. This is therefore a great price package.
Thermostatic valves with adjustable temperature are used in domestic hot water distribution. This type of valve allows you to set the outlet temperature of the mixed water in a given range. The biggest advantage is the possibility of changing the outlet temperature by turning the control wheel. This principle can be used, for example, as protection against scalding - for example, in schools. In buildings with central and long hot water distribution, temperature needs to be maintained at a higher level due to temperature losses. At the individual consumption points, it is then necessary to cool the water to a comfortable level, which can be achieved by means of thermostatic valves with adjustable temperature.
In the catalog you will also find thermostatic valves for balancing the circulation, which are necessary for an even distribution of flow in the entire heating system. For the correct function of the individual elements, it is necessary to balance the flow distribution, which is what these valves are used for.
Balancing of heating systems is done by the help of balancing valves, which can be fitted with thermoelectric actuators. Find out more HERE.
Finally, here is a few questions that you may have when buying or using thermostatic valves.
o Thermostatic valves of the VTA series have a wide range of temperatures, depending on the production material - for brass it is 20 to 43 °C, 35 to 60 °C, 45 to 65 °C, 50 to 75 °C with outlet temperature stability +- 2 °C. Nickel valves are supplied in the temperature range 32 - 49 °C, 35 - 50 °C, 35 - 60 °C and 45 - 65 °C. The outlet temperature stability is +- 1 °C (VTA300 series) and +- 2 °C (VTA500 series).
o For the brass range, hot water is available in 7-8 seconds. For the nickel series, it is available in 2-3 seconds.
o During disinfection, water in the heating system must be heated to 60 °C. This prevents the growth of Legionella Pneumophilla bacteria, which causes so-called Legionnaires' disease or (milder) Pontiac fever. But such a high temperature that effectively kills bacteria could cause scalding. It is therefore necessary to install a thermostatic mixing valve (VTA) in front of the water heater and reduce the water temperature accordingly.
o VTA322 with a temperature range of 20 - 43 °C, covers 40 to 80 m2.
VTA522 with the same temperature range covers 85 - 160 m2.
VTA572 20 - 43 °C can control the area of 130 to 240 m2.
According to the ESBE manufacturer these stated parameters are based on the assumption of a temperature difference of max. 7 K and an underfloor heating output of 50 W / m2.
§ You need to make sure that the minimum temperature difference between the hot water supply and the mixed water outlet is at least 10 °C. Also check that one of the ports is not under excessive pressure from a circulation pump.
§ There are two possibilities - either this problem is caused by low pressure on the supply line, or by a non-functional thermostatic cartridge. If you remove the thermostatic cartridge from the valve and put it in water at a temperature at least 10 ºC higher than its opening temperature, the cartridge should open in a few moments. In this case, there is a problem of unbalanced pressure in the valve.