The principle of operation of the membrane tank. Expansion tank for heating: what is it for, where and which one is better. The principle of operation and types of compensatory devices

As you know from the school physics course, a liquid expands in volume when heated. Since in heating systems the elasticity of the pipes is not high enough to accommodate the increased volume, the pressure rises sharply. This often leads to rupture of radiators and lines. If you don't find a way to drain the excess water, the entire system can easily fail in just a few hours. For this, additional communications are installed, which allow accumulating pressure in closed-type heating.

Principle of operation

Without this auxiliary equipment, normal operation of any space heating system is impossible. The simplest devices make it possible to compensate for the expansion of the heated liquid and avoid water hammer. For this reason, during use, it is imperative to follow the safety rules. It is quite simple to select the necessary unit and carry out the installation. With the right choice of equipment, long-term stable operation of the entire heating system will be guaranteed.

Tank selection

When designing a reliable heating system, everyone will have to wisely choose such a tank and install it in the heating system. The characteristics of the device will depend on the function to be performed and the type of structure to be installed. There are only three options available on the market.

Closed type. The price of such units on the domestic market can vary from 2,500 to 75,000 rubles, depending on the required volume. An ordinary sealed tank is filled with air. As the pressure in the system rises, the tank space is filled by compressing air. A special membrane is installed in the inside of the tank. It is necessary to protect the unit from rust after the water has become corrosive as a result of mixing with oxygen.

An open tank does not have a sealed lid. The average cost in the domestic market is about 3000 rubles. Such devices are used not only to compensate for expansion, but also to remove air locks from the system. A coolant can be added to the structure through such a tank to compensate for its gradual evaporation.

Water heating at home can be designed using a top-filling cistern. This is a sealed container equipped with a valve. With the help of such a tank, you can quickly bleed water from the home heating system as quickly as possible.

Installation instructions

Installation should be carried out in strict accordance with technology for the highest quality operation of heating devices. The device must be installed above the boiler, and the water pipes must be directed downward for the convenience of draining the coolant in case of a membrane breakage.

Such a system is based on forced circulation of energy carriers, so it must be compensated by circulation pumps. A flat expansion tank for closed-type heating is much more difficult to select and install when compared with other types of devices, since they are not designed to compensate for thermal expansion. The stable functioning of the entire system will depend on the quality of the installation.

Such tanks are installed in areas where there are no turbulences in the flow of the coolant. For this reason, the correct location would be on straight pipe sections in front of the circulation pumps. You will have to familiarize yourself with some general rules for the selection and installation of tanks, which must be observed when designing and assembling the system.

Volume calculation

A tenth of the coolant passing through the system should be placed in the tank. In no case should you choose a smaller size, because the pressure in the expansion tank of a closed-type heating will be too high, and it will not be possible to prevent hydraulic fracturing. This calculation is only suitable in cases where water is used as a heat carrier. Select a larger container volume if ethylene glycol is circulating in the system.

Such an expansion tank must be supplied with a special one. It is almost always included in the factory kit. If the tank does not have a valve, you need to buy and install it. The pressure in the expansion tank of a closed-type heating can be reduced thanks to such a device.

If the calculation was carried out incorrectly, and a unit with insufficient volume was purchased, you can buy another one. A frequent increase in pressure in heating systems will serve as a clear sign of a mistake made when choosing a tank.

Accommodation

The height of the tank mounting from the floor will play absolutely no role in this. The tightness will be maintained, and the air will be discharged through special valves. During installation, it is advisable to take into account that the flow of the coolant from above will be the most optimal option. This makes it possible to get rid of the air entering the fluid compartments.

When an expansion tank is selected for closed-type heating, the price of the entire system may be higher when compared with the option of buying two-circuit electric or gas boilers, which already have a mechanism for lowering the pressure.

Suitable amount of water

In heating systems, the required volume of water is determined depending on the size of the room, the power of the boiler and the number of heating elements. In conventional systems, 14 liters are calculated per 1 kW of voltage. This amount should be sufficient for good circulation and normal heat transfer.

Calculation methods

It is not always easy to find a suitable expansion tank for closed-type heating. Installation instructions for a space heating system can sometimes only be carried out with outside help. Each owner can take advantage of several available ways to select the appropriate tank. The easiest way is to find a special calculator program on the Internet that facilitates the calculation according to the specified parameters and makes it possible to determine the size of the tank for full compensation in the system.

You can also address this question to the specialists working in the design bureaus. This is the most reliable and most expensive option. Thanks to this method, you can avoid design errors and prepare it for stable long-term operation.

Some people try to calculate the required volume of the tank using the formulas on their own. In this case, it is necessary to take into account how much the pressure in the expansion tank of a closed-type heating can change. The volume increase coefficient at a coolant temperature of 95 degrees is 0.04, and at 85 o C - 0.034. Specialized programs make it possible to carry out calculations based on the total volume of water in the system, calculated according to the power of heating boilers.

Accurate calculations determine the overall efficiency of heating, ensuring uninterrupted operation, excluding possible malfunctions in the event of disturbances in the operation of the equipment.

The maximum permissible pressure in the expansion tank of a closed-type heating is determined by threshold values. It is desirable that they can be regulated. The volumes of the tanks are initially selected with a margin so that they can perform all the necessary functions in case of inaccuracies in the calculations without creating a threat of accidents. You should not save money when buying, and it is preferable to trust the installation of all equipment only to professionals.

Do not forget that the level of protection of housing from the cold will depend on the reliability of the heating system, since any malfunctions can leave the building completely without heat. Correct installation makes it possible to avoid many problems, and any house will be protected during the most severe cold weather. Naturally, over time, each expansion tank for closed-type heating can be damaged. Malfunctions in the heating system occur from time to time. It is better to seek the help of qualified professionals to troubleshoot all problems.

This type of equipment is separated by rubber baffles. Air is pumped into the upper part of them to supply the initial pressure. The heating medium is supplied to the lower part and the heating installation starts up. As the temperature rises, the amount of water increases and excess water is released into the tank. When the coolant returns to its original volume in the heating system, the pressure is automatically adjusted. The membrane then assumes its normal position.

Tanks with cylinder installation

Such equipment makes it possible to regulate the pressure more accurately. The air chamber is located around the entire perimeter of the tank. The rubber compartment expands when the coolant enters it. The main feature of such membranes is the ability to replace them in case of wear. The rubber material must always comply with sanitary standards and specific requirements for elasticity, heat resistance, duration of possible operation, moisture resistance.

Conclusion

The heating installation must always be equipped with an expansion vessel. This equipment is designed to maintain a stable and constant pressure, ensuring the normal functioning and proper operation of closed-type systems and the circulation of the coolant in them.

The main task of such cisterns is to reduce the possibility of hydraulic fracturing due to the sharp increase in pressure in the pipes. This can lead to malfunctions in the operation of individual elements of the heating system.

An expansion membrane tank is an element of a closed heating system designed to compensate for the thermal expansion of the coolant and maintain the required pressure.

Note! In addition to being used in heating systems, membrane tanks are also used in water supply systems. They "soften" the water hammer that occurs when the pumping stations are turned on / off, and also maintain a constant pressure in the system.

Diaphragm tank design

The expansion membrane tank for heating is a sealed cylindrical steel body covered with red epoxy lacquer (there are also blue lacquered tanks, but they are designed for cold water). There are 2 chambers in the body: gas and water, which are separated from each other by a movable gas-tight membrane (diaphragm) made of butyl rubber. Thanks to this material, the membrane is able to function stably at various temperatures (from -10 to + 100 ° C) and perform up to 100,000 cycles.

The membrane practically completely excludes the interaction of the coolant and gas. The absence of such interaction allows the pre-pressure in the gas chamber to be maintained longer, which has a positive effect on the service life of the tank.

Note! Modern high-quality membranes are not simply pulled out under the pressure of the expanding coolant, but, as it were, "stick" to the walls of the tank. This principle of operation allows to increase the service life of the membrane.

Both chambers have the same pressure, which allows maintaining the tightness of this section of the heating system. The air chamber is filled with a nitrogen-containing mixture. When the coolant expands, nitrogen is compressed, allowing the coolant to "enter" into the water chamber.

Most modern membrane heating tanks have a nipple built into the body (similar to a conventional automobile one), with which you can "pump" the air chamber by increasing the pressure in it. You can do this yourself at home using a pump or compressor. However, it should be remembered that it is recommended to inject nitrogen, and not air. The fact is that the oxygen contained in the air will cause accelerated corrosion of the walls of the tank body, which will inevitably shorten the service life of the device. Nitrogen, on the other hand, is neutral and does not corrode.

The tank body has an external threaded outlet for easy installation. Depending on the model, the thread can be:

For low pressure tanks (from 0.5 to 1.5 bar) - 3/4 ″ or 1 ″;
For medium pressure tanks (1.5 bar) - 1 ″;
For high-pressure tanks (from 3 bar and above) - from 1 "to DN 100 flanged connections;

The principle of operation of the diaphragm tank

When the heating system starts up, the coolant heats up and increases in volume. This excess volume moves into the water chamber of the expansion vessel. After the coolant has cooled down, the pressure in the air chamber squeezes out the membrane, thereby displacing the coolant from the water chamber back into the heating circuit.

In addition, as noted above, the membrane tank maintains the required pressure in the entire heating system. So for example, if somewhere there was an insignificant leak of the coolant, then the pressure should drop in the entire system, but this does not happen, because the pressure in the air chamber will push the membrane and, with it, the coolant back into the system, thereby creating a limited make-up.

The coolant is in constant contact with air, which leads to the airing of the system and the appearance of air locks. Therefore, it is necessary to regularly remove air or is required. Otherwise, air can lead to corrosion of individual elements of the heating system, as well as to a decrease in heat transfer from heating devices;
Due to the constant presence of the coolant in contact with air, it evaporates. You have to regularly add coolant to the system;
Air microbubbles circulating through the heating system create unpleasant noises in pipes and radiators, and also lead to premature wear of parts. In addition, microbubbles "de-rate" the circulation pump;
Unlike the membrane tank, which can be installed at any point in the system (next to the boiler, in the basement, ...), the open-type expansion tank is installed only at the highest point. This leads to an increase in the cost of the system, because additional pipes and fittings must be used to mount the tank at the highest point.

For any closed heating system, a device must be provided to compensate for the expansion of the coolant. This is necessary to preserve the integrity of the pipes, radiators and the boiler heat exchanger. In addition to the standard air vent, membrane tanks for heating systems must be installed: installation, calculation, the principle of operation of which directly affects the heating efficiency of a residential building.

Purpose and features of membrane heating tanks

First you need to know the functional qualities of this device. When water is heated in pipes, natural expansion and pressure increase occurs. If the value exceeds the standardized value, a stabilization mechanism is required. It is for this purpose that membrane tanks for heating systems are intended, which may differ in technical and design characteristics.

They represent a sealed container, divided into 2 areas - water and air chambers. An elastic membrane is located between them. To connect the water, a corresponding branch pipe is provided, and a pressure build-up system is located in the air chamber. The principle of operation of an expansion membrane tank for a heating system is to increase the usable volume as a result of the displacement of the elastic membrane towards the air chamber. To do this, it is necessary to connect a water pipe to the heating pipe, and create a pressure in the air chamber, the value of which should not exceed the nominal value for the heating system.

Installing a membrane tank in a heating system has the following advantages:

Automatic stabilization of the critical expansion of the coolant;
No water loss due to evaporation;
Can be installed both for a system with distilled water and antifreeze;
Simple installation and replacement of the membrane when its service life is exceeded.

But how to choose the right membrane tank for heating, the principle of operation of which is so simple? To do this, you first need to familiarize yourself with its varieties.

A membrane tank for heating is similar in principle to that for a water supply system. But the design of the latter is not designed for high temperatures. Manufacturers mark them in blue, and heating ones in red.

Types of membrane tanks

At first glance, the design of the device is quite simple. However, for different heating systems with specific technical characteristics, the correct model of membrane expansion tank for heating must be selected. Consider the most popular models that can be installed in both a household and an industrial system.

Fixed tank

Their feature is that the membrane tank for heating according to the instructions is not collapsible. those. the elastic membrane cannot be removed and replaced with a new one. Despite this seemingly disadvantage, these models have one significant advantage - affordable cost. That is why they are installed for small heating systems with relatively stable pipe pressure. Often, the calculation of a membrane tank for heating implies a constant pressure in the air chamber, which the manufacturer specifies additionally. But if there is a likelihood of exceeding the critical expansion rate of the coolant, it is necessary to install a different type of structure.

Flanged with replaceable diaphragm

To install a new membrane, a flange is provided in the structure on which it is mounted. Thus, you can adjust the volume of the membrane tank for heating, install elastic lotions with different elasticity indicators. Such models are installed for heating systems with a high probability of excess pressure in the pipes. First of all, this applies to solid fuel boilers, where it is impossible to quickly adjust the water heating level. Tanks can be made of horizontal and vertical type. To replace the diaphragm, it is necessary to remove the flange, dismantle the old one and install a new one in its place. The most popular manufacturer of such models is the Wester company, a membrane heating tank that can be found both in a small private house and in the heating system of a production workshop.

The usable volume of a membrane heating tank depends on its shape. For large systems, it is best to choose cylindrical structures, and flat models will be optimal for heating with a short pipe length.

Calculation of the diaphragm tank

However, the choice of design is not the only parameter of membrane tanks for the heating system. An important quantity is the volume in one chamber, namely, its filling factor. The correct calculation of a membrane tank for heating is impossible without the following parameters:

The total volume of the coolant in the system is C. As you know from the school physics course, when the temperature rises for every 10 degrees, the liquid increases by 0.3%. This is what will primarily affect the volume of filling the tank;
The maximum and minimum pressure in the system. Often, the critical value does not exceed 5 atm;
Fill factor (Kzap). It directly depends on the pressure indicators in the pipes. In the table you can find the required value for a specific diaphragm tank. In the instructions, the manufacturer indicates the nominal value of the fill factor.

You should also take into account the coefficient of expansion for water E, which is 0.034 at 85 ° C. Further, the calculation is performed according to the formula. Suppose that the total volume of the heating system is 410 liters, the minimum pressure is 1 atm, and the maximum pressure is 3.5 atm. The filling factor will then be equal to 0.55, and the useful volume of the tank is equal.

This is the optimal calculated volume of the membrane tank for heating. If necessary, it can be changed upwards, but not more than by 15%.

An accurate calculation of the volume of a membrane tank for heating is recommended only after reading the instructions from the manufacturer. It contains all the necessary data for calculations, as well as possible errors and deviations.

Tank installation steps

For a qualified installation of a membrane tank in a heating system, it is necessary that the room meets the operating conditions. The temperature in it should not drop below 0 degrees with a stable indicator of humidity. It is necessary to determine the place of installation, since the system is characterized by pressure drops during start-up. Therefore, it is not recommended to install expansion membrane tanks for heating immediately after the boiler on the outlet pipe.

The next criterion is the absence of turbulence in water flows that can simulate overpressure. It is best to mount membrane tanks for heating systems on the return pipe in front of the circulation pump. Installation technology consists in performing the following steps:

Pipeline tie-in. Typically, the expansion vessel nozzle diameter is 3/4. Therefore, a suitable threaded channel must be installed in the return pipe;
Installation should not be impeded by objects or system elements. External mechanical stress on the tank is excluded;
It is best to use paronite models as gaskets, as they withstand pressure and high temperatures well;
The diaphragm expansion tank for heating must be equipped with an air valve. It is necessary to stabilize and regulate the pressure in the air chamber.

Each time a closed heating system is started, an increased pressure will act on the membrane. Therefore, it is recommended to check the condition at least once every 2 years and, if necessary, replace it.

This is a typical installation diagram that does not take into account the characteristics of a particular heating system and its constituent elements. During installation, frequent mistakes should be avoided, which can lead to incorrect functioning of membrane tanks for heating systems. First of all - setting the maximum pressure in the air chamber. It should be 10-15% less than the calculated critical value. Otherwise, the membrane will not expand towards the chamber, which will lead to a burst of pipes and failure of heating radiators. To avoid this, it is necessary to install a pressure gauge, which is recommended by Wester, whose membrane heating tanks are characterized by high reliability.

To install a membrane tank in the heating system, make sure that there is no such tank in the heating boiler. If its volume is not enough according to calculations, you can mount an additional tank.

First of all, it is necessary to determine the design of the membrane expansion tank intended for heating. If critical pressure surges are not expected, the total volume of the coolant is small - an inexpensive fixed type model can be selected. In all other cases, membrane tanks are required for collapsible heating systems, since it is much cheaper to change the elastic membrane than the entire structure. In addition, when choosing, one should take into account the following factors:

Case metal thickness. It must be at least 1 mm;
Protective inner and outer coating. Since all membrane tanks designed for heating systems are made of metal, corrosion processes should not affect their integrity;
Reduction of heat losses due to an additional insulating layer. The relatively large volume of the water chamber can negatively affect the decrease in the temperature of the water in the pipes. If the design does not provide for a heat-insulating layer, you can make it yourself using polyethylene foam or a similar material;
Pay attention to the design. According to the instructions, the membrane tank for heating can be horizontal or vertical. Installation in any other position is prohibited.

And most importantly, you should only purchase models from trusted manufacturers. These include expansion tanks for heating from Wester. Along with it, the products of the companies Zilmet (Italy), Aquasystem (Italy) and Sprut (China) are characterized by good quality indicators. Their average cost ranges from 2 to 5 thousand rubles, depending on the volume.

Despite the good operating characteristics, a drain safety valve is installed in addition to the expansion membrane tanks of the heating system. If the pressure in the pipes exceeds the critical value even for the expansion tank, the valve will remove excess water.

The diaphragm expansion tank is an indispensable component of the heating system, without which it is impossible to fully heat the room in the cold season. With the help of this device, critical changes in the volume of water are compensated, which are the result of its heating.

Tank device

If the heating system does not include an additional device, into which an excess volume of liquid can pass, then it may fail. The role of a spare tank is played by a membrane tank, which is necessary for smooth operation.

Membrane

The reservoir housing has an elastic membrane that divides its inner chamber into two parts. One part contains a coolant, and the other is filled with air. Nitrogen can be used instead.

Depending on the model, the device may include a replaceable or non-replaceable membrane. In the first case, the coolant is placed in an elastic cavity and does not come into contact with the metal inner surfaces.

Installation (or removal) of the membrane is carried out through the flange, for which bolts are used. Such manipulations are performed when the equipment is being repaired.

If the device has a non-replaceable membrane, then it is equipped with an internal cavity of two sections. Dismantling in this case is not provided.

To protect the system from overpressure, the diaphragm tanks are equipped with safety valves.

Operating principle

The principle of operation of the device is based on the change in the volume of liquid during heating and cooling.
In a closed loop, the water, heating up, expands, while the pressure in the entire network increases. The excess volume of liquid enters the expansion tank, where it reduces the amount of air by stretching the membrane between the chambers.

As the temperature drops, the pressure in the system drops and air displaces water from the tank. Water from the tank will continue to flow until the pressure equilibrates.

Application area

Diaphragm tanks are widely used. They are embedded in systems such as:

heat supply from heat;
heating system connected to the central heating line according to an independent scheme;
heating powered by solar collectors and heating ducts;
any systems with a closed loop and variable temperature of the working environment.

Advantages

The invention of a closed expansion tank with a membrane made it possible to increase the working life of the entire heating system. The device has the following advantages:

allows the use of water of any composition, incl. hypercalcified;
a membrane made of butyl and natural rubber allows the use of equipment for drinking water;
the principle of operation and the membrane design of the device can ensure the reception of a significant amount of the displaced liquid;
easy installation;
minimal losses from evaporation;
low operating costs.

Scheme of use in the heating system.

The compact dimensions of the flat membrane tank allow an economical use of room space, so it is best suited for oversized rooms.

The expansion tank does not allow the occurrence of increased loads in the heating system and is an effective means of preventing emergencies.

Equipment selection

First of all, the volume of the coolant for the heating system is taken into account. If the selection is not performed correctly and the volume is not enough, then cracks and water leaks will appear at the joints.

In addition, pressure may drop below a safe minimum. This will lead to the airing of the internal cavity of the tank, then urgent repairs will be required. Therefore, it is better to select a model based on the characteristics that the accompanying instructions contain.

The value of the initial pressure in the expansion vessel connected to the cold heating network must match the static pressure of the system. The permissible discrepancy between the indicators can be + 30-50 kPa.

This table will help you calculate the required tank volume.

The tank must have a volume of at least 10-12% of the total volume of the heat supply network in which it is used. This will exclude the possible failure of both the reservoir itself and the entire heating system as a whole during a pressure surge.

When choosing a suitable model, you should also take into account the maximum allowable pressure at which the device can function.

Diaphragm tanks protect the heating system from excessive temperature rise and regulate the pressure level in it. Therefore, such devices are equipped with independent temperature and pressure sensors.

Mounting the device

The installation is carried out in such a way that subsequent maintenance can be carried out without hindrance.
The new tank, as a rule, has an excess initial gas pressure that spreads throughout the entire volume. Before installing the expansion tank, it must be inflated to the previously calculated pressure.

The diaphragm tank must be installed before branching the water supply. It is necessary to ensure the drainage of water and make-up of the system. The room must be maintained at a positive temperature.

Additional loads on the tank are unacceptable! If the container has a volume of 8 to 30 liters, then wall mounting is allowed. For large volumes, the equipment is placed on its legs.

Grounding must be carried out to prevent electrolytic corrosion.

Setting up the device

In order not to wonder how to check the pressure, it is advisable to install a pressure gauge at the outlet. To remove excess air, it is rational to supplement the equipment with an automatic valve.

The set of the required pressure is carried out in strict sequence. First, the pressure is released through the nipple or using a compressor. Then connect the device to the heating system and fill it with water. The process does not stop until the pressure in the system and in the tank is the same.

When arranging the heating system, it is necessary to pay attention to absolutely all points, from the design of the heating unit to its complete set. Among all the variety of functional elements, a vacuum expansion tank for heating plays an important role in creating high-quality heating equipment. Thanks to this device, the volume of the coolant is regulated, which eliminates the rupture of the heating main, radiators and shut-off valves.

The principle of operation and types of compensatory devices

If you are going to equip a heating unit in a country house, then an expansion tank for heating (expansomat) must appear in it without fail.

The scheme of operation of the expansion tank for heating is simple: with an increase in the temperature regime of the coolant, its volume (we are talking about water, since it is it that is most often used for piping heating units) increases. Due to the fact that the circuit is closed, the liquid does not evaporate or burn, which, in turn, provokes an increase in pressure in the line, which must be reduced in order to avoid an emergency. This stabilization of pressure in the heating system is called compensation, and it is for these purposes that an expansion tank for heating is used.

Types of expansomats

Until recently, heating units were widely used that worked by means of gravitational circulation of the coolant, that is, without centrifugal pumps. Open-type expansion tanks were installed for them. But at the same time, such devices had a lot of shortcomings, so today they are practically not used for piping thermal blocks.

And the thing is that air entered the open expansomats, which provoked the development of corrosion on the inner surfaces of the heat exchangers. In addition, the liquid from the system was regularly evaporated, which required constant monitoring of its amount, since this could lead to a decrease in the efficiency of the entire heating unit. And besides, such tanks should be located at the highest point of the system, which is not always convenient and practical.

Modern heating blocks are characterized by the use of pumping units and closed-type expansion tanks. In this case, the advantage is that the heating circuit is completely sealed.

The scheme of operation of the membrane expansion tank of the heating system is based on the following principle: inside it there is a membrane that divides the expansomat into two parts. One half contains air or gas, which is pumped into it under pressure. Whereas at the expense of the other part, the amount of liquid is directly adjusted. The membrane for the expansion tank is made of an elastic material, which causes the air chamber to contract when water enters it, the pressure in it increases, thereby compensating for the increased pressure in the heating circuit. When the coolant is cooled, the opposite process takes place.

Buried type expansomats can be flanged (with a replaceable membrane block) and one-piece (with a non-replaceable membrane). The second option is the most preferable due to its favorable cost. But at the same time, flange expansion joints are much better in terms of performance, since if the membrane ruptures, it can be replaced with a new one without any problems.

Choosing an expansion tank

The choice of a heating system compensator is quite important, so you need to take it seriously. An important aspect of choosing a compensator is:

type - closed or open;
standard size;
membrane properties:
resistance to diffusion processes;
working temperature;
operational period.

You can find out all these data directly in the store where you will purchase the expansomat.

How to calculate the volume of the expansion joint?

First, we will determine the dependence of the required volume and the parameters that affect it. When calculating, it is necessary to take into account the fact that the larger the volume of the thermal circuit and the higher the maximum permissible temperature regime in it, the larger the size of the compensating tank should be.

So, to determine the volume of the expansion tank, you can use the following formula:

K ov is a coefficient that shows the size of the increase in the cubic capacity of the coolant when it is heated.

According to research data, for every 10 ° C increase in the water temperature in the main line, it becomes 0.3% more. In simplified calculations, a figure of 5% is used. In the event that a non-freeze (antifreeze) circulates along the thermal circuit, this value will be from 8 to 10%, depending on the type of anti-freeze liquid.

V vk - the volume of water in the line.

This data is taken from the calculations of the project, which were carried out at the stage of drawing up the diagram of the heating unit. In the event that you do not possess such data, then you will have to determine the cubic capacity of the coolant yourself. This can be done by draining the fluid from the pipeline. The amount of water is measured with buckets or a flow meter, which is installed on the stream.

R dk is the maximum allowable pressure of the boiler and the entire circuit as a whole. This value is taken from the rating data of the heating element.
P db is the pressure indicator in the air compartment of the regulator, which is indicated by the manufacturer in the technical passport of the unit.

Based on the calculation results, you will receive an accurate value.

The installation of the expansion tank of the heating system is carried out in accordance with all the rules for the installation of such equipment, which are regulated by the project and the instructions of the manufacturer of the equipment. The installation of an open-type compensator is carried out at the highest point of the heating main. Whereas closed tanks are placed anywhere, but not immediately after the pumping unit.

When installing compensating tanks, it is necessary to pay special attention to its fasteners, since its mass together with the liquid is large enough.

As a rule, such equipment is equipped with all the necessary fasteners, however, according to user reviews, they are far from always able to ensure reliable fixation of the tank.

In addition, during the installation of this functional device, it is worth thinking about the fact that it should be convenient for you to use it.

Features of the maintenance of the compensating tank

regular checks for corrosion, dents and smudges - at least once every 6 months;
checking the initial pressure of the gas space for compliance with the calculated indicator - at least once every 6 months;
checking the membrane for deformations and damage - at least once every 6 months;
storage of an unused tank is carried out in a dry place.

That is, in fact, all the subtleties of the device of this functional equipment. We hope this publication will help you equip your home with an efficient heating system.

VIDEO: Overview of expansion tanks with a volume of 2-12500 liters with fixed and replaceable membranes and automatic expansion systems controlled by compressors

Many devices are used in heating and water supply systems. One of the main ones is the membrane tank. With its help, pressure drops are smoothed. Diaphragm tank for heating system, principle of operation which is based on improving the quality of the heating system, consists of a sealed barrel with a flange.

In this way, it connects to the pipeline system.

Diaphragm tank device

The equipment is presented in the form of a sealed vessel, divided into two sections:

The air section includes pressurized air.
The water section is attached to the heating. It passes water of various pressures through itself.

An elastic membrane separates the compartments, due to which it changes in shape. Therefore, the volumes of these compartments change. The air compartment contains a valve with a nipple, which changes the pressure. With its help, the functioning of the membrane tank is regulated.

Air pressure influences water flow as well as volume and pressure.

Principle of operation

As the water compartment increases, the tank expands. As a result, it fills with a lot of water. And the air department gets smaller. The air pressure then decreases, thereby balancing the water pressure. When the pressure in the system decreases, the membrane contracts, after which the lost pressure is replenished.

The water supply in the membrane tank will continue until the air and water pressure are balanced.

Diaphragm tank functions

For the heating system. Heating water leads to an increase in its volume, which requires the use of expansion tanks. With their help, the expansion of the water is compensated. The size of the device must correspond to the heating system: the volume "dampens" the expansion of the water. If there is no membrane tank, then heating leads to defects in the heating system. As a result, the entire system may fail.
In a water supply device, a membrane tank is used instead of a hydraulic accumulator, due to which water accumulates, after which its consumption occurs as intended. For operation, the pressure present in the accumulator is used, and a pump is not required in this case. Since the pump operates infrequently, its service life is extended. As a hydraulic accumulator, it performs the function of water compensation when hot water is connected.
Water hammer protection function. If you suddenly turn on the pump for supplying water, then such an overlap leads to the appearance of a water hammer. It assumes a pressure drop, due to which the pipeline and the entire mechanism fail. The membrane tank will perform the function of protection: due to the high pressure, the membrane will stretch, the water section will be large, and the pressure will decrease.

The use of such equipment is useful in many areas of equipment operation. Therefore, its presence in the heating system is very important.

The expansion tank is a very important element in the heating system. It prevents pressure build-up in the heating system when it heats up. Tanks can be open and closed. Open tanks have a number of disadvantages that are not found in membrane tanks. They are bulky, have a lot of heat loss, and do not work under high pressure. Diaphragm tanks are more perfect, and they do not have the same drawbacks that open ones have.

What is a diaphragm expansion tank

An expansion tank is an important element in heating, because it prevents the coolant from boiling, which can lead to bad consequences.

Such tanks can used in different systems:

with heat pumps and solar collectors;
with an autonomous heat source;
connected to the central heating network according to an independent scheme;
with closed contours.

Diaphragm tanks regulate the pressure in the heating system in case of its increase and with pressure drops, which prevents emergency dangerous situations and times of malfunction of heating systems.

The expansion membrane tank can be with fixed and replaceable baffle. The first ones are made with an internal cavity divided into two parts by a securely fixed membrane, which is located along the perimeter of the section.

Tanks with a replaceable partition differ from fixed ones in that the coolant is in the membrane tank and does not come into contact with the steel surface. Membrane assembly and disassembly simple enough through a bolted flange.

Advice... When installing the membrane tank, it is necessary to securely attach it, because during operation, the mass of the tank increases.

Benefits of diaphragm expansion tanks

Expansion tanks have a huge number of advantages:

do not pollute water;
low costs during operation;
easy installation;
safety, reliability;
installation in any part at home;
impossibility of pouring water out of the tank;
no heat loss;
minimum air supply;
membranes made of natural rubber and butyl can be used in drinking water supply;
used for any type of water;
convenient to use;
radiator and boiler due to lack of contact between water and air last longer, than usual.

Expansion membrane tanks are used in closed heating systems and ensure reliable boiler operation.

Advice... When choosing a membrane tank, you should give preference to closed-type tanks, which are much better than open ones.

Diaphragm expansion tank design

flat or balloon metal body inside divided by a rubber membrane. One part contains air or gas, which is compressed to a certain required level. The air compression level can be found in the passport. The other part of the tank in working order will be filled with water and due to this the level of gas compression will be the same as in the entire heating system. Compressor in tank maintains the pressure in the air chamber.

One of the most important elements of a diaphragm expansion vessel is the diaphragm, which can be of two types:

balloon;
diaphragm.

Diaphragm valves are used in tanks with a small volume and cannot be replaced. Balloon can easy to replace if necessary, this type of expansion tank is also more reliable due to the fact that the water is in the membrane and does not touch the tank body.

Advice... When choosing a diaphragm expansion tank, you need to pay attention to the material from which the diaphragm is made.

Diaphragm tank selection

In heating systems, the membrane load, like the expansion of water, does not change very much, but the temperature of the heating of the liquid can be about 90 ° C.

When choosing an expansion membrane tank, special attention should be paid give to the material from which the membrane is made. The material must be of high quality, reliable and resistant to high temperatures and extremes.

You should also pay attention to the following characteristics of the membrane:

range working temperatures;
long life time;
sanitary and hygienic requirements;
resistance to impact high temperatures;
dynamism.

Advice... When choosing an expansion membrane tank, it is necessary to select tanks with a strong and reliable body so that it lasts longer.

Calculation of the volume of the expansion membrane tank

In order to determine the volume of the expansion membrane tank, it is necessary to determine the total volume of the heating system, which consists of several volumes:

pipeline;
heating device;
boiler.

The easiest way to determine the required volume of the tank is calculate 10% of the total volume of the heating system. If it is 500 liters, then you need a tank with a volume of 50 liters.

If the volume of the expansion membrane tank is less than necessary, this will lead to bad consequences. Cracks will begin to appear, hot water will leak through the threads, and the tank itself can deteriorate very quickly and it will have to be changed.

The membrane tank is selected individually for each heating system.

Advice... If safety valves are installed in a closed heating system, pressure build-up can be avoided and the entire system protected.

Installation of an expansion membrane tank

You will need skill and knowledge to install and connect a membrane tank to a heating system. You should not undertake the installation of the tank yourself if you are not sure that everything will be done correctly.

To install you will need:

step key;
gas wrench;
plastic pipes;
adjustable wrench.

When installing a membrane expansion tank in a heating system, you need to be very careful and careful check the tightness connections.

The expansion tank must be sealed, it cannot be disassembled, opened, it just connects to the pipeline which is closest to the boiler . It is also necessary to install safety devices to prevent pressure build-up.

When installing the tank, it is necessary take into account a few rules:

Advice... In order to extend the service life of heating systems, it is not necessary to use oxygen-containing water and corrosive gases.

Possible breakdowns

The most common breakdown of a diaphragm expansion tank is considered membrane rupture in case of exceeding the permissible pressure and uneven loads. Replaceable membranes break much more often than pressed ones, because for the latter, more durable materials are used, since they can be changed at any time, but pressed ones do not.

Due to the rupture of the diaphragm, if it is not replaced, the tank will eventually falls into disrepair, because water gets on the inner surface of the tank and it becomes unusable under the influence of corrosion.

The quality and reliability of the diaphragm expansion vessel is also influenced by the choice of material from which it is made. Quality material will cost much more.

Diaphragm expansion tanks are an important part of the heating system, because it is thanks to them that it is possible to control the pressure in the heating system. To select a tank, you need take into account the individual characteristics of the system and pick it up.

Tank device

Membrane

The reservoir housing has an elastic membrane that divides its inner chamber into two parts. One part contains a coolant, and the other is filled with air. Nitrogen can be used instead.

Installation (or removal) of the membrane is carried out through the flange, for which bolts are used. Such manipulations are performed when the equipment is being repaired.

If the device has a non-replaceable membrane, then it is equipped with an internal cavity of two sections. Dismantling in this case is not provided.

To protect the system from overpressure, the diaphragm tanks are equipped with safety valves.

Operating principle

As the temperature drops, the pressure in the system drops and air displaces water from the tank. Water from the tank will continue to flow until the pressure equilibrates.

Application area

Diaphragm tanks are widely used. They are embedded in systems such as:

heat supply with an autonomous heat source;
heating system connected to the central heating line according to an independent scheme;
heating powered by solar collectors and heating ducts;
any systems with a closed loop and variable temperature of the working environment.

Advantages

The invention of a closed expansion tank with a membrane made it possible to increase the working life of the entire heating system. The device has the following advantages:

allows the use of water of any composition, incl. hypercalcified;
a membrane made of butyl and natural rubber allows the use of equipment for drinking water;
the principle of operation and the membrane design of the device can ensure the reception of a significant amount of the displaced liquid;
easy installation;
minimal losses from evaporation;
low operating costs.

Scheme of use in the heating system.

The compact dimensions of the flat membrane tank allow an economical use of room space, so it is best suited for oversized rooms.

The expansion tank does not allow the occurrence of increased loads in the heating system and is an effective means of preventing emergencies.

Equipment selection

This table will help you calculate the required tank volume.

When choosing a suitable model, you should also take into account the maximum allowable pressure at which the device can function.

Mounting the device

Additional loads on the tank are unacceptable! If the container has a volume of 8 to 30 liters, then wall mounting is allowed. For large volumes, the equipment is placed on its legs.

Grounding must be carried out to prevent electrolytic corrosion.

Setting up the device

In order not to wonder how to check the pressure, it is advisable to install a pressure gauge at the outlet. To remove excess air, it is rational to supplement the equipment with an automatic valve.

The stability, reliability, efficiency and durability of the heating system depend on how correctly all its parameters are calculated, how harmoniously its devices, units and necessary devices interact with each other, how well the installation and adjustment are performed. And there can be no trifles in such matters.

It would be completely unreasonable to divide individual devices and nodes into "important" and "not so". Yes, the cost of elements can differ very significantly, the functionality of some is always in sight, while others are completely invisible and even incomprehensible, from the point of view of an inexperienced user... But each fulfills its own "mission" in the overall work of the system. Therefore, for example, the question looks completely amateurish - is the expansion tank so important for the heating system, and is it worth giving importance to the problem of its choice and correct installation? Meanwhile, the importance of this simple device is difficult to overestimate.

Why is an expansion tank necessary in principle?

This is the easiest question to answer. Even someone who did not study very well in high school probably knows simply from life experience - when heated, physical bodies increase in volume. And water is no exception in this regard.

It is interesting that water has another unique quality - it begins to increase in volume and when it cools below the threshold of +4 ° WITH, that is, during freezing - a transition to a solid state of aggregation. But this does not apply to the topic of our consideration now.

Thermal expansion is characterized by a special value - the coefficient. This, specifically for water, is a non-linear indicator that largely depends on temperature. The coefficient itself shows how many times the volume increases when the liquid is heated by 1 degree.

We will not present the entire table of coefficients for water here. It is better to illustrate this extension with a known physical experiment.

So, on the left side of the figure, a tank is shown, to which, up to the overflow hole, exactly 1 liter (1 dm³) of water with a temperature of + 4 ° is placed WITH... This value is the zero reference point for water. A measuring container is installed under the overflow pipe.

The water in the tank starts to heat up. With an increase in temperature, the density of water decreases, that is, while its mass remains equal, an expansion of the volume is observed. When heated to a temperature of + 90 ° WITH about 36 ml of water is collected in a measuring container - this is a volume that has become excessive and passed through the overflow pipe.

Is it a lot or a little? It seems to be nonsense. But if we look at it on a more serious scale, then with a change in temperature, very significant fluctuations in volume are obtained. Judge for yourself - with 100 initial liters, we would already be talking about 3.5 liters of excess.

If you leave water in a closed volume, then it will have nowhere to expand - it is an incompressible body. Therefore, according to the laws of thermodynamics, pressure begins to rise under such conditions. But this is already serious. If the pressure in the closed circuits of the heating system exceeds the permissible threshold, then it will still be a successful outcome if everything is limited to flow at the pipe connections or. But an uncontrolled increase in pressure can bring much more destructive consequences.

In order not to bring the situation to even minor accidents, an additional container must be provided in the heating system, which would be able to receive and give off excess water (or any other liquid heat carrier) formed during its heating. This is the task assigned to the expansion tanks. However, even their name speaks for itself.

With the generality of the main function, the design of the expansion tanks may differ. And the main difference lies in the features of the heating system itself, which can be open or

Expansion tank in an open-type heating system

The specifics of the location of the open tank

The features of such a system are probably already clear from its name. The circuit is, of course, closed, but it is not isolated from the atmosphere, leaking, and there can be no excess pressure in it, by definition. And the expansion tank is an ordinary container embedded in the circuit. The main condition is that it should be located above the highest point of the system.

Expansion tank prices

expansion tank

Why the highest point? Everything is simple - otherwise, the liquid will simply pour out according to the law of communicating vessels.

In addition, this arrangement contributes to the performance of another important function - the open-type expansion tank becomes an effective air vent. There is always dissolved air in water, which is able to pass into a gaseous state familiar to itself. In addition, chemical reactions between the coolant and the material of pipes and heat exchangers can lead to the release of gases. And the accumulation of gas can lock the radiator or even an entire section of the heating circuit. So the timely removal of gas bubbles is extremely important.

True, sometimes open expansion tanks crash into the return line (for one reason or another). But all the same - this is the highest point of the system, to which a vertical pipe is simply laid. In this case, the gas trap function does not work, and this will require the installation of additional valves on the radiators and, again, at the highest point of the system on the supply pipe.

Design options

What is the design of an open expansion tank? It can be the simplest one or have some improvements. In any case, this is a container of a certain volume, which is usually covered with a lid on top. The cover is only needed to protect against debris or dust entering the water, and is never sealed. That is, the current atmospheric pressure is always maintained in the tank. A v the container itself has nipples embedded - from one in the simplest version, to several, for various purposes.

Expansion tanks of an open type can be purchased ready-made - the stores offer a fairly wide range of products of various sizes. Most often they are made of stainless steel or galvanized steel sheet to prevent corrosion.

But many craftsmen prefer to make such tanks on their own. The container is quite possible from sheet material, and often ready-made ones are used - for example, metal or even plastic barrels or canisters, old gas cylinders, etc. All this will cost very inexpensively, and it will not be difficult for a good owner to make an appropriate cut-in of the pipes.

Let's take a look at several possible layouts of such tanks:

The simplest scheme - a branch pipe is simply cut into the container from the bottom, which is connected to the heating circuit.

It is clear that with this design, there is no circulation of the coolant through the tank will not. When filling the system, ensure that the water level in the tank is approximately in the middle of its height. And fluctuations in the volume of liquid in the system will be reflected by an increase and decrease in this level.

Of course, control is needed over the level of the coolant in the tank - evaporation, one way or another, will be, and if you do not replenish the water, then you can cause an air blockage of the system circuit or "airing" of the radiators. So you will have to look into an expansion tank of such a simple design regularly in order to make recharge if necessary.

Various tricks are used to facilitate visual inspection. In particular, it is possible to embed from the side of the tank small diameter branch pipe, on which a short piece of transparent hose is put on. It is clear that the water level in the hose will correspond to the level in the tank - a quick glance is enough to assess the situation.

But it has already been said that the tank should be located at the highest point, and very often the attic becomes this place. That is, the container is not in plain sight, and it is extremely inconvenient to climb up every time to check the level. But this control can be organized in a different way. An example is shown in the diagram below:

Two branch pipes are cut into the tank from the front side.

The upper one (pos. 1) determines the maximum permissible filling of the container, and simply works for overflow. From it, a pipe (hose) is drawn into the sewer or even simply discharged onto the ground - into the garden.

A pipe is connected to the lower branch pipe (item 2), which goes into the room, on which an ordinary ball valve is located in a convenient place for the owners. The height of the embedded branch pipe determines the minimum permissible water level in the tank. That is, to control the fullness, you just need to open the tap - if water comes out of the pipe, then everything is normal. Otherwise, make-up is carried out until water flows through the overflow pipe.

Convenient for punctual owners who remember the need for regular monitoring. But for the forgetful and such a scheme is unlikely to become a "helper". But it is quite possible to "automate" the process of maintaining the level in the tank at the required level. To do this, it will be enough to bring a make-up pipe (from the water supply) to the tank, but connect it through a float valve, which is usually used in toilet cisterns.

That is, the overflow pipe will protect against overflow (it is necessary in any case), and such a simple make-up system will not allow a critical drop in the level.

All the schemes shown above can be figuratively called "passive" - the coolant does not circulate through the expansion tank. This simply creates free space for the expanding volume of liquid. It is not difficult and quite efficient. But there is also a drawback - the function air vent in such tanks is very unproductive. A considerable amount of air bubbles entrained by the flow of water when following the supply line will simply slip past the place where the branch pipe is inserted to the expansion tank. And in order for the tank to become an effective air separator, circulation is often closed through it. That is, it becomes a link in the general water circulation loop.

It might look something like this:

The coolant is supplied to the tank through a pipe 1 , and through the branch pipe 2 it enters the supply line again. A sharp increase in volume (at the transition from the pipe diameter to the tank), accordingly, causes a sharp decrease in the flow rate, which contributes to the ascent and release of the smallest gas bubbles into the atmosphere. Pipe position 1 it can be different, for example, it can be supplied from below. But in any case, its welded pipe inside the tank should be located above the outlet

Overflow pipes (pos. 3) and make-up in such circuits are no different from the options shown above. It's just that not everything is indicated here, so as not to overload the picture.

Of course, if such an expansion tank connection scheme is used, then steps are being taken for its very high quality thermal insulation. Otherwise, completely unproductive and very large heat losses are possible, especially if the tank has to be located in an unheated room.

By the way, the scheme shown above can have further development. You can find examples when the function of the distributing manifold is also assigned to the expansion tank, if the heating system is organized according to the principle of risers.

In this case, they try to place a well-insulated tank as close as possible to the geometric center of the house. And already from it, the hot coolant is dispensed along the risers of the system through the embedded nozzles.

How much tank volume is required?

Now about what should be the volume of an open expansion tank. There are no strict rules on this matter. Everyone can, knowing the value of the coefficient of thermal expansion of water, the capacity of their heating system and its expected temperature mode of operation, estimate how much the volume of liquid will increase.

Based on the above values, one would assume that since heating 100 liters of water to 90 degrees gives an increase in volume of 3.5 liters (that is, in fact, 3.5%), then one can proceed from the norm of 5% of the system capacity. But practice shows that this is clearly not enough. Do not forget that the tank must be pre-filled to at least a quarter of its height (this is the minimum) - so that the system does not "grab" a portion of air. Further, the same "variable volume" is provided, which will compensate for the expansion. Approximately at the upper boundary of this volume, an overflow pipe is cut. Well, above the water level, there must be free space to the lid. That is, you cannot keep up with 5 percent.

The experience of the masters involved in the installation of heating shows that the best solution would be to proceed from the following approximate ratio: tank volume ≈ 10% of the system volume.

This means that you need to know the volume of your system. How do I find it?

If the heating system is ready, then the easiest way will be to detect with a water meter how much will fit into it until it is completely filled. Reception is very accurate, but very little helpful. Agree, usually the capacity of the tank is calculated in advance, and not after the installation of the circuits.
With a very large error, but still you can accept the ratio: 15 liters of water for each kilowatt of boiler output... It is clear that with this approach, it is not difficult to make a mistake.
Finally, the volume of the heating system can be easily calculated. It must be assumed that if it is planned to install an expansion tank, then the system design already includes the mounted contours of pipes of one type or another, and the model of the boiler, and the types of heating radiators, and their number. That is, if you sum up the volumes of all elements of the system, you can find the desired value.

The task may seem daunting. But in fact it is not so scary - if you use our online calculator, to which the link leads (it will open on a separate page).

JILEX expansion tanks prices

expansion tank JILEX

How to calculate the total volume of the heating system?

The selection of an expansion tank is far from the only case when this parameter will become necessary. For example, this is required when buying antifreeze coolant, when carrying out some calculations of mixing units, etc. With our calculator calculation common volumeheating systems the reader will perform the calculations without much trouble.

Please note - if the calculations are made in order to determine the optimal volume of the expansion tank, then the tank itself should be excluded from the calculations. It's easy to do - just move the slider to the "0" position.

Disadvantages of an open heating system

So, let's summarize the expansion tank in open heating systems.

By the way, such systems completely prevailed not so long ago. If only for the reason that it was simply impossible to buy equipment for a closed-type system. But today, alas, they have to be recognized as obsolete.

Explicit dignity simplicity of design is seen. In some cases, it is practically not necessary to purchase any additional materials at all. If desired, a completely functional tank can be made "on the knee" from the "trash" stored in the garage.
In an open system, a priori, dangerous pressure cannot arise, since it is associated with the atmosphere. This obviates the need for a safety valve.
We add to the advantages the ability of the expansion tank to act as air vent.

But disadvantages the open system also has quite a few:

It has been noted more than once that the tank should be installed at the highest point in the system. It is good if the house has an insulated attic. But this does not always happen, and it is necessary to provide for a very high-quality insulation of the container, so that it simply does not "grab" in a severe frost.
If the tank has to be installed indoors (for example, there is no attic at all), then it, placed under the ceiling, will clearly not become an interior decoration.

The water level in the tank needs constant monitoring. This problem, as we have seen, is solvable, but nonetheless.
Moreover, due to leaks, there is a constant process of water evaporation. The coolant from contact with air is saturated with oxygen, which activates corrosion on the metal parts of the circuit and in the boiler heat exchanger.
If you have noticed, the discussion above was exclusively about water as a heat carrier. In open systems, it cannot be otherwise - the evaporation of expensive antifreeze looks wasteful. In addition, many antifreezes when evaporated are not at all safe for health. So if an open heating system is planned in a house that often remains empty in winter, you will have to drain the water from it.
Such a system is not possible if an electrode boiler is used. Its work is based on the principle of electrical conductivity of the coolant, that is, the chemical composition is of great importance. And with uncontrolled evaporation, the optimal concentration will quickly be lost.
A stable low system pressure is not always an advantage. Some heating devices, on the contrary, show their advantages precisely at increased pressure indicators.

As you can see, there are a lot of shortcomings. Therefore, a closed-type heating system is considered more perfect. But it uses a completely different expansion tank.

Expansion tank for closed heating system

The main advantages of such a tank can be considered its compactness and the ability to install on any part of the heating system. The fact that it is often drawn on diagrams mounted on a "return" pipe in the immediate vicinity of the pumping unit is, indeed, a recommended position. But there are no serious restrictions on the choice of another place.

Expansion tank prices Wester

expansion tank Wester

The fact that the tank is sealed means that the pressure in the system can rise to very significant levels. This predetermines the need for a "security group" in the loop. Such a group traditionally includes a safety valve set to a certain upper pressure threshold, automatic air vent and instrumentation - pressure gauge or pressure gauge combined with a thermometer.

It is unlikely that this can be fully attributed to the shortcomings - rather, these are the operational features of the system. So the only "disadvantage" of a closed expansion tank can be considered the need to purchase it. But it is not a sin to pay for the comfort in using the system.

By the way, many modern heating boilers, especially wall-mounted ones, are already initially equipped with a built-in expansion tank of the required volume. So you don't have to buy or install anything.

The device and principle of operation of the expansion tank for a closed heating system.

The tank device is pretty simple. The design may vary slightly, but the principle is the same in all models.

And the principle is that the hermetically sealed volume is divided into two chambers by an elastic partition. One chamber, water, is connected through a branch pipe to the heating system circuit. The second is air, in which a certain level of pressure is preliminarily created.

The device can be illustrated by the following diagram:

The tank body (item 1) is usually a prefabricated stamped metal structure. The cylindrical shape is "classic" but there are other options, inside the walls are treated with an anticorrosive compound, a protective enamel coating is applied outside. The color should be red. The fact is that there are also accumulator tanks, which both externally and in their structure differ little from expansion ones. But their blue color suggests that they not calculated to work in high temperature conditions. So there is no complete interchangeability here.

There is always a threaded pipe (item 2) installed on the body, through which the expansion tank will be connected to the heating circuit. Some manufacturers immediately complete their products with fittings with an American union nut - so the process of installing the tank will be even easier.

On the opposite side of the body there is usually a nipple or spool (item 3), very similar to a bicycle one, through which the air chamber is pumped to the required pressure level in it.

The main part of this design is the diaphragm (pos. 6), which divides the internal volume of the tank into two chambers. It is made from a material with high elasticity and extremely low diffusion rate. Previously, rubber was more often used for these purposes, but such membranes still did not differ in durability. Modern devices usually use ethylene-propylene or butyl.

So, the membrane divides the tank into a water chamber (pos. 4) located on the side of the branch pipe, and into an air chamber (pos. 5) from the side of the nipple. And the volume of these chambers is a variable quantity.

As already mentioned, an overpressure is preliminarily created in the air chamber (usually in the range from 1 to 1.5 atmospheres). Under its influence, the membrane falls down, and the water chamber has a minimum volume before filling the system.
The system is filled with coolant and started up. In this case, a certain operating pressure is created in the circuit (optimal for this system). At the same time, the membrane bends somewhat - the volume of the water chamber has increased.
As it heats up, the coolant increases in volume. The only place in the system where this "surplus" can fit is the water chamber of the tank. This means that its volume increases even more, and in the air chamber, which has significantly decreased because of this, the gas pressure increases.
The coolant cools down, decreasing in the total volume - the gas pressure pushes the membrane down. That is, the necessary balance is achieved at any time, the optimal pressure value is maintained in the system.
Well, if something went wrong, and the coolant has nowhere to expand (for example, the thermostatic automation of the system failed), then the safety valve of the "safety group" will work, bleeding off excess fluid and restoring balance - until the cause is identified and eliminated.

By the way, in some models of expansion tanks, the presence of a safety valve is provided in their very design.

The membrane can also have other shapes. So, balloon-type tanks are widely used. The features of their device are shown in the diagram below.

In such tanks, the membrane is made in the form of an elastic balloon (item 1), the edges of which are hermetically fixed in a flange with an inlet pipe (item 2). In fact, this balloon becomes the water chamber of the tank. And the rest of the space is an air chamber (pos. 3) with a preset pressure in it. When the coolant expands, the walls of the cylinder stretch, it acquires a pear-shaped shape (fragment on the right). The volume of the air chamber decreases, the pressure in it increases - and then everything, as in already described above example.

By the way, such tanks are quite popular because it is not difficult to replace a membrane that has come out of a standing position in them - thanks to its flange fastening. Diaphragm tanks very often simply cannot be repaired.

How much volume should an expansion vessel have in a closed heating system?

On sale there are lines of models of expansion tanks with a wide variety of volumes. Which one to choose for his systems? To determine this parameter, it is best to make a small calculation.

The formula for the calculations is as follows:

Vb =Vs ×k / D

We decipher the designations:

Vb- the required volume of the tank (minimum).

Vwith- the total volume of the heating system. How it can be determined has already been discussed above.

k- coefficient of thermal expansion of the coolant.

Here is a little more detail. The fact is that if antifreeze is used instead of water, then the expansion rates can be completely different, and depend on both the temperature and the concentration of glycol additives.

The table below will help you find the right value:

Heating agent heating temperature, ° С	Glycol content,%
	0% (water)	10%	20%	30%	40%	50%	70%	90%
0	0.00013	0.0032	0.0064	0.0096	0.0128	0.016	0.0224	0.0288
10	0.00027	0.0034	0.0066	0.0098	0.013	0.0162	0.0226	0.029
20	0.00177	0.0048	0.008	0.0112	0.0144	0.0176	0.024	0.0304
30	0.00435	0.0074	0.0106	0.0138	0.017	0.0202	0.0266	0.033
40	0.0078	0.0109	0.0141	0.0173	0.0205	0.0237	0.0301	0.0365
50	0.0121	0.0151	0.0183	0.0215	0.0247	0.0279	0.0343	0.0407
60	0.0171	0.0201	0.0232	0.0263	0.0294	0.0325	0.0387	0.0449
70	0.0227	0.0258	0.0288	0.0318	0.0348	0.0378	0.0438	0.0498
80	0.029	0.032	0.0349	0.0378	0.0407	0.0436	0.0494	0.0552
90	0.0359	0.0389	0.0417	0.0445	0.0473	0.0501	0.0557	0.0613
100	0.0434	0.0465	0.0491	0.0517	0.0543	0.0569	0.0621	0.0729

D- coefficient of efficiency of the expansion tank. It, in turn, is determined by the following formula:

D = (Qm – Qb) / (Qm + 1)

The following values are covered under the letter designations:

Qm- the upper threshold of the permissible pressure in the heating system. That is, this is exactly the indicator under which the actuation force of the safety valve in the "safety group" is adjusted.

Qb- pre-created pressure in the air chamber of the expansion tank. If the tank already has such a pumping, then this value will be indicated in the passport. But often the pressure is set independently using a conventional automobile pump and with control by the same automobile pressure gauge. The value has already been mentioned - as a rule, in the range from 1.0 to 1.5 atmospheres.

In order not to force the reader to carry out calculations manually, below is a convenient calculator that will perform the calculation in literally seconds.