In many domestic machines, the cooling system is similar to the heating system. The design has a circulating pump. As a rule, expansion tanks are installed open type. However, this is not very convenient. In closed systems, membrane tanks are used. Their design, which has a relatively small size, is designed for fairly high temperatures. Connection is made using pipes of small diameter.
In a closed, fluid-filled system, as the water temperature rises, the hydraulic pressure tends to increase. Too high a pressure can lead to the failure of individual parts. Expansion tanks for heating systems are used to exclude such situations. They are used to compensate for the volume of liquid, which becomes larger when heated, and any attempts to compress water lead to an increase in its volume.
The expansion tank of the membrane type (closed) is made in the form of a sealed metal ball or oval. The volume of water should be able to increase. The expansion tank has an internal space divided into two parts . Air is pumped into one. The second half of the space is attached to the system. During heating, the air is compressed.
The expansion tank (closed) requires the installation of a manual pressure control nipple or safety valve and pressure gauge. This is to prevent overpressure. For an autonomous heating system with artificial circulation, a certain pressure is set. As a rule, its value is two or four bars.
An expansion tank is installed next to the boiler. The connection is made to the return pipe in front of the pipe (suction) of the circulating pump. Of great importance should be attached to the fasteners of the tank itself, since in the process of work its mass will increase significantly. The whole structure is a metal housing. It can be flat or balloon type. Air is pumped into the air chamber. He is under a certain pressure. The initial pressure is indicated, as a rule, in the design passport. The entire volume of the unconnected expansion tank is occupied by air.
Before starting, it is necessary to set the gas charging pressure equal to the static pressure. It is installed at the rate of one bar per ten meters of the water column located above the structure. With increasing temperature, water enters the water chamber, thus increasing the pressure in the airspace to the pressure in the entire system. With a larger volume of coolant, a prerequisite is control over the gas pressure in the air cavity. In this case, the expansion tank is equipped with a compressor that keeps the pressure in the air compartment at a constant level.
There is one main element throughout the design. This element - the membrane - can be diaphragm or balloon type. The former are non-replaceable and are usually used in small volume designs. In case of failure of the balloon type membrane, it can be replaced. The advantage of this design is also the lack of contact between water and the housing. The fluid is located inside the membrane. This greatly increases the life of the entire structure.
The expansion tank has a certain volume. For its calculation, special values are used. The main one is the total volume in the entire heating system. If this volume is unknown, then it is calculated in accordance with the capacity of the boiler and taking into account the type of heating appliances.