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.
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.
