Type
General type of the vessel.
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Water pressure tank. Water pressure tanks are called auxiliary tanks used in water supply systems. Such a reservoir consists of an external rigid body (usually metal) and an internal cylinder — a bladder made of an elastic material, in which there is a supply of water. This bladder can compress and stretch when the volume of the liquid in it changes, and this liquid itself does not come into contact with the outer walls of the tank (this is one of the key differences between water pressure tanks and expansion tanks). As for the application, such vessels perform several functions at once. Firstly, they ensure the maintenance of a stable pressure during pressure drops in the water supply system. Secondly, the water pressure tank effectively dampens water hammers, protecting the more sensitive components of the system from them. Thirdly, the supply of water in such a reservoir will come in handy in the event of a complete shutdown of the water supply. Thus, the volume of water pressure tanks is quite large — in most models from 20 litres or more; exceptions are extremely rare.
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Expansion tank. A kind of auxiliary tank used in heating systems. Such products differ from the water pressure tanks described above, firstly, by their relatively small volumes, and secondly, by their design: instead of a bladder, a membrane is installed inside, dividing the internal
...space into two parts, and the water in the tank is in contact with its outer walls. Expansion tanks are used to compensate for fluctuations in the volume of the coolant with changes in its temperature. So, if the temperature rises and the liquid in the system increases in volume, its excess enters the tank, which avoids a critical increase in pressure and damage to the circuits. When the temperature drops, accordingly, the required volume of water is returned from the tank to the system.
We emphasize that different types of tanks are not interchangeable: the use of an expansion tank instead of a water pressure tank (and vice versa) is fraught with several unpleasant consequences.Capacity
Nominal capacity of the water pressure tank or expansion tank.
For normal operation of the tank, this volume must be at least a certain value. However, the calculation methods depend on the type of container (see above). So, for water pressure tanks, the total number of consumers (total water consumption) and pump performance are taken into account, for expansion tanks — the volume of the circuit, the thermal expansion of the coolant and temperature fluctuations. Detailed recommendations about these calculations can be found in special sources; another option is to contact a heating/water systems expert. We only note that instead of one large tank, it is quite possible to install several small ones — in the second case, their total volume will have a value.
As for the specific volume values, in most water pressure tanks it ranges from
11 – 25 litres to more than 100 litres (
101 – 150 litres ,
151 – 200 litres and even
more). At the same time, even small water supply systems are often equipped with very capacious water pressure tanks — to have a supply of water in case of failures in the water supply. In turn, the expansion tank does not require significant volumes to perform its tasks, so such products do not differ in capacity — many models hold
10 litres or less(although there are
...exceptions).Maximum operating pressure
The highest operating pressure allowed for the tank.
This parameter must not be lower than the constant operating pressure in the heating/water supply system. However, the specific values depend on the type of system and the type of tank (see above). So, for a water pressure tank, the maximum operating pressure must be higher than the shutdown pressure of the pump. In general, rather high-pressure values are found in water supply systems, so most modern water pressure tanks fall into one of the following categories:
6 bar,
8 bar,
10 bar and
more than 10 bar(although there are models with more modest values).
In turn, the expansion tank must withstand the pressure at which the safety valve in the heating system is activated. Most of these tanks are designed for
3 bar,
4 bar or
5 bar — heating systems rarely use higher pressures (although exceptions are possible here).
In general, when choosing this parameter, the rule “the more the better” works quite well: a good pressure margin will provide an additional guarantee in case of emergencies. The reverse side of this reliability can only be called a slightly increased price.
Connection size
The size of the thread used to connect the auxiliary tank to the heating or water supply. In modern plumbing, standard diameters are used, indicated in inches and fractions of an inch — for example, 2" or 3/8". This indicator must correspond to the characteristics of the tank — otherwise, at best, you will have to use adapters, and at worst, the tank will be completely unsuitable for installation.
Usually, the larger the tank, the larger the connection used to install it (otherwise it would be impossible to provide the necessary throughput at the connection point).
