Comparison water Pressure Tanks

General type of the vessel.

— 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.

— 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.

The regular way to install an auxiliary tank. Regardless of the type (see above), modern products can use both horizontal and vertical installation methods. It does not affect the main functionality, therefore, choosing a model according to this indicator is based on which option is most convenient for the intended installation location. We note only two specific points. Firstly, if the installation location allows, then it is better to use horizontal models for pumping stations, and vertical models for submersible pumps. Secondly, as it is used, air accumulates in the tank, which inevitably enters there along with water; it accumulates at the top of the tank and is much easier to bleed when installed vertically than when installed horizontally. However, this is only true for vessels with a special valve; in the absence of such a valve, the air can only be removed by completely emptying the tank (regardless of the method of installation).

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).

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.

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).

The material from which the tank is made.

— Carbon steel. A relatively simple and inexpensive type of steel. At the same time, this alloy is strong and reliable, it is resistant to temperature extremes and high pressures. The main disadvantage of carbon steel is that it is inevitably susceptible to corrosion from contact with water. However, for water pressure tanks (see "Type") this moment does not matter, because it is not water that contacts the tank walls, but an elastic balloon. In expansion tanks, in turn, various solutions can be used to protect the inner walls — for example, special coatings. And even without such coatings, the tank rusts rather slowly, its service life is usually calculated at least for years, and little rust is released into the coolant. Therefore, most modern water pressure tanks are equipped with carbon steel tanks (for additional reliability, individual elements in such models can be made of stainless steel).

— Stainless steel. A type of steel that stands out, by the name, with high corrosion resistance: even with constant contact of water with such an alloy, rust does not appear on it. Accordingly, stainless steel tanks are extremely reliable and durable. On the other hand, they are many times more expensive than similar carbon steel containers, and rust resistance is not so critical (see above for more details). Therefore, this option is used rarely and...mainly in water pressure tanks.

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.

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 wat...er 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.