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(alt
...hough there are exceptions).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).
Flange material
The material from which the flange of the water pressure tank or expansion tank is made (see "Type").
The flange is a disk located on the side or bottom end of the vessel (in a horizontal and vertical arrangement, respectively). In the centre of the disk is a pipe used to connect the tank to the system. One of the main functions of the flange is precisely the fixation of the pipe in the tank; in addition, in water pressure tanks, an internal membrane is attached to this element using a counter flange.
The flange is one of the most sensitive structural elements to corrosion; that is why the material of this part is important; it is specified in the specs separately and may differ from the material of the container itself. The most widespread nowadays are flanges made of
carbon steel and
stainless steel,
plastic products and combinations of metal with plastic are much less common. Here is a more detailed description of each option:
— Carbon steel. It is steel with a high carbon content, supplemented with a special coating, and is the most popular material for flanges today. The main advantages of this material are ease of production and low cost. On the other hand, such steel is not particularly resistant to corrosion. The mentioned coating (most often zinc) somewhat improves the corrosion resistance. However, this type of flange is
...still not particularly durable: their guaranteed service life is from 4 to 6 years, after which the part will have to be changed. For the same reason, carbon steel is not recommended for drinking water systems. However, many consider this material to be optimal in terms of price and durability/quality.
— Stainless steel. Steel with a special composition that provides high resistance to corrosion (hence the name). From this follows the main advantages of such flanges — high reliability, durability and hygiene; the latter allows you to use "stainless steel" without any special restrictions, even for drinking water supply. However, this material is much more expensive than carbon steel.
— Plastic. Plastic combines the advantages of carbon and stainless steel: on the one hand, this material is inexpensive, on the other hand, it is not subject to corrosion. At the same time, such flanges are not durable, which makes them difficult to use in high-pressure vessels and, in general, reduces reliability. Therefore, this material is not popular.
— Metal/plastic. Combined designs that combine a metal base (usually carbon steel) and a plastic inner liner. It allows you to combine the advantages of both materials and partly compensate for the shortcomings: steel provides overall strength, and plastic, which is not afraid of corrosion, is in contact with water. On the other hand, such parts are relatively difficult to manufacture and therefore are rare.Membrane material
The material from which the internal elastic membrane of the tank is made.
Recall that in water pressure tanks (see "Type") this membrane has the form of a kind of balloon, which is filled with water so that the liquid does not come into contact with the metal walls of the tank. In turn, elastic transverse partitions are installed in the expansion tanks. However, in both cases, one of three materials is usually used for the membrane:
EPDM (ethylene propylene diene rubber),
Butyl (butyl rubber) or
SBR (styrene-butadiene rubber). Here is a more detailed description of each of these options:
— EPDM (ethylene propylene diene rubber). The most popular material for membranes nowadays is both in water pressure tanks and in expansion tanks. This prevalence is due to a combination of reliability, practicality, safety and affordability. Thus, EPDM has high elasticity and a wide operating temperature range, tolerates an average of up to 100K cycles of stretching/compression within acceptable limits, does not react with oxygen and industrial alcohols and can be used in drinking water supply systems. However, in terms of overall strength and resistance to diffusion, this material is somewhat inferior to butyl rubber (see below), but it is also much cheaper.
— Butyl (butyl rubber). High-quality material used primarily in water pressure tanks for
...cold water systems. One of the key advantages of butyl rubber is excellent gas tightness — several times higher than that of EPDM; simply put, much less air penetrates through such a membrane, which allows the tank to work longer without special maintenance. Also, this material is characterized by high strength, solvent resistance and hygiene; the latter allows the use of butyl rubber even in drinking water systems. The main disadvantage of this type of membrane is its high cost.
— SBR (styrene-butadiene rubber). A material primarily used in expansion tank membranes. This specialization is because SBR does not tolerate frequent tension compression very well and is better suited for static loads, which are just typical for such containers. At the same time, this material is reliable, elastic, resistant to water hammer, and very slightly permeable to air. Its unambiguous disadvantages include unsuitability for systems with drinking water.
