Expansion tank for heating systems. Diaphragm expansion tank How a heating expansion tank works

Nowadays, a membrane expansion tank has become very popular as a compensating device for coolant. Gravity heating systems with natural circulation are used quite rarely, and therefore open containers are gradually becoming a thing of the past. Modern water supply systems, where pumping stations and indirect heating boilers are installed, also require such devices. This material will tell you how to select and connect such a tank to a particular system.

Design and principle of operation of a membrane tank

Let's start with the fact that structurally, devices intended for heating and water supply (hydraulic accumulators) have some differences and should not be confused with each other. At the same time, the operating principle of a membrane tank is the same regardless of its design.

The general structure of such tanks is as follows: inside a sealed cylindrical metal body there is a rubber membrane (popularly called a “pear”). It comes in two types:

• in the form of a diaphragm dividing the internal space approximately in half;
• in the shape of a pear, its base attached to the water inlet pipe.

Note. The second type of membrane must be replaced; to do this, you need to unscrew the flange of the pipe. The first type cannot be replaced, only together with the body.

The difference between the vessels for different systems is that membrane expansion tanks for heating systems are filled with coolant that is in contact with the metal walls from the inside. In water supply containers, water never comes into contact with metal, and some models even provide for flushing the bulb. These modifications are recommended for use in drinking water supply networks.

Another difference is that membranes for water expansion tanks are made:

• from food rubber;
• adapted to higher pressure than for heating ones.

Accordingly, the “pear” in the tank for heating systems is adapted to operate at a higher temperature. The very principle of operation of the devices is simple: under the influence of external forces (thermal expansion or the influence of a pump), the container is filled with water and stretches the membrane to known limits. An increase in the “pear”, on the other hand, limits the air under a certain pressure. To create this pressure, the tank design provides a special spool.

When the external influence stops and the pressure in the pipeline network drops due to water withdrawal or cooling of the coolant, the membrane gradually pushes water back into the system.

Let's start with the fact that a membrane expansion tank for water supply cannot be used in heating networks and vice versa. The reason is that each system has its own pressure and temperature, as well as requirements for water quality. Meanwhile, they are very similar in appearance; manufacturers even manage to paint the tank bodies the same color (most often red). How can you tell the difference?

Each product is attached to a plate with inscriptions - a nameplate. It contains all the information we need. When the nameplate says that the maximum operating pressure is 10 Bar and the temperature is 70 ºС, then in front of you is an expansion tank for cold water supply. If the inscription says that the maximum temperature is 120 ºС and the pressure is 3 Bar, then this is a membrane heating tank, everything is simple.

The second selection criterion is the volume of the tank, it is determined as follows:

• for a heating system: the total amount of coolant in the home network is calculated and a tenth of it is taken. This will be the capacity of the tank with a reserve;
• for water supply: here the volume of the vessel must ensure comfortable operation of the water pump. The latter should not turn on and off more than 50 times per hour. A sales representative will help you determine the figure more precisely;
• for DHW (boiler tank). The principle is the same as with heating, only you need to take a tenth of the capacity of the indirect heating boiler;

Attention! To compensate for the thermal expansion of water in the boiler, you need to take a tank designed for water supply.

How to properly install a membrane tank

Not only the performance of a particular system, but also the service life of the tank depends on how correctly the membrane-type expansion tank is installed and connected. The first thing to do is to place and secure the tank to the wall or floor in the position required by its instruction manual. If there is nothing about this in it, then below in the text we will clarify this issue.

The second point is that a shut-off valve must be installed on the supply pipe. By closing it, you can always remove the membrane pressure tank for repair or replacement. And in order not to flood the floors of the furnace room, it is worth providing a drain fitting and another tap between the shut-off valve and the container. Then it will be possible to empty the tank before removal.

Tanks for heating systems

In a situation where the documentation for the tank does not prescribe how to correctly orient it in space, we advise you to always place the tank with the inlet pipe down. This will allow it to work in the heating system for some time if a crack appears in the diaphragm. Then the air at the top will not rush to penetrate the coolant. But when the tank is turned upside down, the lighter gas will quickly flow through the crack and enter the system.

It doesn’t matter where to connect the tank supply – to the supply or return, especially if the heat source is a gas or diesel boiler. For solid fuel heaters, installing a compensating vessel on the supply side is undesirable; it is better to connect it to the return line. Well, at the end, adjustment is required, for which the device of the expansion membrane tank provides a special spool on top.

The fully assembled system must be filled with water and the air vented. Then measure the pressure near the boiler and compare it with the pressure in the air chamber of the tank. In the latter it should be 0.2 bar less than in the network. If this is not the case, it must be ensured by bleeding or pumping air into the membrane water tank through the spool.

Tanks for water supply systems

Unlike expansion tanks for heating, hydraulic accumulators can be oriented in space however you like, it doesn’t really matter. It will also be useful to install fittings on the supply line to the tank to cut it off from the network and empty it.

But the settings for cold and hot water supply are different. The fact is that the pressure in the pipelines is created by a pump that has an upper and lower shutdown threshold. You need to navigate by them. The pressure in the membrane tank operating in the cold water supply circuit must be set to 0.2 Bar less than the lower pump shutdown threshold. This will avoid water hammer in the system.

As for DHW, here the air pressure in the tank should be 0.2 Bar greater than the upper shutdown threshold of the pumping station. This is necessary to ensure that water does not stagnate in the container. You can find out more useful information by watching the video:

Conclusion

It would seem that such a simple unit as a water tank, but it requires so much scrupulousness in detail. In fact, a serious approach is needed when installing any element of a home network, otherwise equally minor troubles will befall you very soon.

Due to temperature fluctuations, the volume of the heating system coolant may change, which can lead to accidents. Therefore, we need to do everything to ensure that it works stably and that this does not happen.

For this purpose, special devices are used, for example, a membrane expansion tank. It is one of the key components of the heating circuit.

Purpose, pros and cons

When the coolant heats up, the pressure in the heating system circuit and boilers increases due to an increase in the volume of liquid. Since it is an incompressible medium and the system itself is sealed, this can lead to pipe or boiler failure.

Some people believe that to solve the problem it is enough to install a valve to squeeze out the excess volume of heated media, but this is not so. When cooling, the liquid will compress, and air will enter the circuit in its place, which will become an obstacle to circulation. Therefore, the air will need to be constantly vented from the radiators, and adding new coolant and heating the water will be very expensive.

For this reason, it is recommended to install a membrane expansion tank for heating. It is a reservoir connected via a pipe to the system. Excessive pressure in it will be compensated by volume, which will ensure full operation of the circuit. The expander takes in a certain amount of liquid as volume and pressure increase, and then, when these indicators decrease, returns it back. Such devices differ from similar devices of other types a number of advantages:

• they can be used in any water, even if it contains a lot of calcium;
• allowed to be used for drinking water;
• have a large useful displacement volume (compared to tanks without a membrane);
• air pumping is required in a minimum amount;
• installation is quick and does not require large expenses;
• operating costs will be minimal.

But it has an expansion tank and disadvantages. Sometimes you may encounter problems when installing it, since it is quite large. Heat loss increases due to the fact that the coolant transfers heat to the expansion chamber.

In addition, there is an increased risk of rust formation in such devices. To avoid uncontrolled heat loss, it is recommended to insulate the device.

Selecting an expansion tank for heating and water supply systems

How and where to install a heating expansion tank

Product design

Indoor heating networks can have open and closed circuits. The first type is used in centralized networks, thanks to which water can be directly withdrawn for hot water needs. The devices are placed at the top of the circuit. Expansion tanks will not only allow you to control the process of pressure drops, but will also perform the function of separating air from the system. If it is of the closed type, then a design with a membrane inside is used.

A membrane-type expansion tank has a relatively simple device. It includes a water reservoir and a rubber membrane, which can be a balloon or diaphragm type.

If the membrane is of the first type, then the coolant is located inside a rubber cylinder, and nitrogen or air is located outside. Such a part can be replaced if necessary, which will save on repairs and not replace the entire device.

The diaphragm membrane for the expansion tank is a permanent partition based on thin metal or elastic polymer.

It has a small capacity and compensates for minor pressure differences. If it fails, it is impossible to replace it, so the tank will have to be replaced completely. But compared to a balloon membrane, it is cheaper.

Expansion tank. Operating principle, selection, inflation pressure

Principle of operation

For each system, the gas pressure is adjusted according to the instructions for the device. The type of membrane does not affect the efficiency of the device. But if it is of the balloon type, more heat-carrying liquid can be placed in the tank. Operating principle of a membrane expansion tank for a heating system It is the same for structures of different types:

Constant pressure is adjusted automatically. In order for the system to work stably, you need to choose the right tank and make calculations. The required pressure cannot be generated if the tank is larger than needed, and if it is smaller, it may not contain excess liquid. This could cause an accident.

Selection rules

In order for a product to work fully, you need not only to select it correctly in terms of volume, but also to take into account its other characteristics. You should pay special attention to the following nuances:

Now on the market you can see a large number of models of Russian and foreign production. They differ in cost, but a suspiciously low price should alert you. This may be due to the fact that low-quality materials of Chinese origin were used in production. Domestic models are much better in quality, they are cheaper than foreign analogues from well-known brands, but are not inferior to them in terms of characteristics.

As already mentioned, the main characteristic that you need to focus on when buying a tank is its volume. Some experts recommend choosing products whose size is within 10% of the total volume of coolant in the heating system. The fact is that the coefficients of thermal expansion, even with high heating, cannot be higher than 0.08. Therefore, calculations should be carried out as accurately as possible, taking into account indicators such as:

• maximum permissible pressure of the heating system;
• coolant volume;
• initial pressure in the tank;
• coefficient of thermal expansion.

When selecting the volume, you need to take into account all the components of the heating system. This can be found out by studying the design documentation. If it is missing, then you can perform an approximate calculation, based on the fact that 1 kW will account for 15 liters of water. The coefficient of thermal expansion of the coolant is determined using the composition of the liquid. In apartment buildings it often contains glycols, which improve its performance.

The coefficient can also be calculated based on the coolant temperature. The maximum pressure of the system is determined using the minimum value allowed for the components. The transition valve is adjusted to it. The initial pressure in the system, provided the coolant is cooled, corresponds to the minimum pressure. On some devices it is adjusted by pumping or bleeding air. The pressure in the tank is controlled by installing a pressure gauge.

The use of a membrane tank for heating has a number of limitations depending on the manufacturer, design and material of manufacture. In some cases, the requirements for the composition of the coolant are very strict. In particular, this concerns limiting the amount of antifreeze and ethylene glycol in its composition.

In addition, expansion tanks cannot be used when pressure limits are exceeded. It is also mandatory to establish a security group that limits and controls it.

Installation requirements

Installing a membrane tank with your own hands is not so difficult; it is not necessary to hire a specialist for the work. The installation requirements are as follows:

If the container has a volume of 30 liters or more, it is prohibited to attach it to supporting structures. Most often it is equipped with special legs and placed on the floor. When installing, it is recommended to follow these tips:

• the pipe must have a three-quarter circumference; accordingly, a similar threaded channel must be present in the return;
• installation is carried out so that parts of the system or other objects do not interfere with the work;
• It is recommended to use paronite gaskets that are resistant to high temperatures or pressure;
• To regulate or maintain the pressure in the gas compartment, the conservator must be equipped with an air valve.

If the system is closed, then each time it is turned on, high pressure is applied to the membrane. Therefore, you should check its condition at least once every 2 years and replace it if necessary. In some cases, everything changes completely.

During installation, gross mistakes must not be made, otherwise the equipment will not function normally. The most common miscalculation is the incorrect indication of the maximum pressure in the gas compartment, which is about 90% of the critical one. If this is allowed, the membrane will not expand towards the compartment. As a result, the pipe will burst, due to which the heating radiators will not be able to work. To correct the error, you need to install a verified pressure gauge. You also need to make sure that there is no tank in the boiler itself. If after calculations it is determined that its volume is small, then additional capacity will be required.

The expansion tank in the heating system is very important. It depends on how correctly it will work. Installing it is not difficult, but you need to pay special attention to this process, since even a small mistake can cause an emergency in the future.

An autonomous heating system must have an expansion tank for heating, or a compensator. Its function is to compensate for the excess pressure that occurs in the system when the coolant expands due to heating. With a rapid increase in temperature, the coolant liquid expands and a pressure surge occurs, the so-called water hammer. It can destroy pipeline elements and connecting fittings. Other names for expansion devices: hydraulic accumulator, expansomat.

Design and principle of operation of expansion tanks for heating

Heating systems can be open or closed. Accordingly, heating expansion tanks exist in open and closed types.

Open type tanks

An open expansion tank for heating is a parallelepiped-shaped container made of stainless steel. This tank is placed at the highest point of an open heating system, usually in the attic.

Pipes connected to the tank:

• mainline;
• circulation;
• alarm, with locking device.

In this type of heating system, the coolant (water) circulates naturally, without pumps. Despite the comparative cheapness and simplicity of such heating, it is gradually becoming a thing of the past due to numerous shortcomings.

• In an open tank, the coolant constantly evaporates, so you need to monitor the water level and add it as necessary. For the same reason, it is problematic to use another coolant, such as antifreeze - it evaporates even faster.
• It is possible for water to overflow from the tank, so it is necessary to ensure its drainage into the sewer or drainage system.
• An open expansion tank requires good thermal insulation so that the water does not freeze in severe frosts.
• Installation in the attic will require additional pipes and connecting elements.
• Air entering the system from the expansion device provokes corrosion of the pipeline and radiators, and also leads to the appearance of air locks.

A system with an open compensator is suitable for heating small one-story houses. Larger houses are heated with closed systems.

Closed tanks

A closed, or membrane expansion tank of a heating system contains an elastic membrane inside, which divides the internal volume of the compensator tank into two compartments, gas and liquid. The gas part contains air under pressure (in some models - nitrogen or inert gas), and the liquid part receives excess coolant when heated.

Closed tank (membrane)

The higher the temperature, the more the liquid part of the accumulator is filled. At the same time, the gas part contracts and the pressure in it increases. When the threshold value is reached, the safety valve is activated and excess pressure is released. And when the heating system cools down, the reverse process occurs and the coolant returns from the tank to the pipeline.

Operating principle of a membrane expansion tank

There are two types of membrane compensators.

1. With a diaphragm type membrane. These are small sized tanks. The diaphragm membrane in them is non-removable and cannot be replaced: if it breaks, you will have to completely replace the device.
2. With a balloon (pear-shaped) membrane. It can be changed when worn out; it is used in large thousand-liter tanks.

The volume of expansion tanks for heating can vary widely from two to several thousand liters. The shape of the closed hydraulic accumulator is flat or cylindrical. In a flat expansion tank, the membrane-diaphragm is located vertically, in a cylindrical tank it is horizontal.

It is worth paying attention: a membrane compensator is sometimes mistakenly called a vacuum expansion tank for heating. However, this device does not use a vacuum. The heating system may have a vacuum deaerator to remove air microbubbles from the water.

Installing a membrane expansion tank

Unlike an open one, a membrane accumulator can be installed directly at the heating point, next to the boiler, for ease of maintenance. Usually it is placed in a straight section in front of the circulation pump, preferably so that water (or other coolant) enters the compensator from above. It must be equipped with a pressure gauge, a safety valve and connected to the return line.

Hydraulic accumulators with a volume of up to 30 liters are mounted on the wall, larger ones are installed on the floor. When mounting on a wall, the tank should be securely fastened, since its weight increases sharply when filled with water.

Several membrane tanks in a heating point

Important performance characteristics and compensator volume calculation

When selecting an expansion tank, take into account the maximum operating temperature and pressure. For example, the coolant can heat up to +120° C, and the peak pressure in the heating expansion tank can reach 6-10 bar (the usual average value is 2-4 bar). Therefore, the characteristics of the membrane, its durability, heat resistance, and compliance with sanitary standards are important.

The volume of the compensator depends on the volume of coolant as a whole in the system. It is not necessary to calculate the volume mathematically accurately; a simplified method is often used: select a tank with a capacity equal to 10% of the total volume of the coolant. And if this volume is unknown, then they proceed from the power of the boiler and the type of heating devices. The ratios are as follows: for heating radiators they take – 11 l/kW, for heated floors – 17.5 l/kW, for wall-floor heaters – 7.5 l/kW.

If the capacity of the selected compensator is insufficient, the safety valve will release pressure too often. In this case, it is enough to purchase and connect in parallel another expansion tank.

It is quite difficult to take into account all the nuances, especially since in each house the heating system necessarily has its own characteristics. In order not to make a mistake when choosing and installing a device, it is better to contact a specialized company.

Video: installation of an expansion tank

Diaphragm expansion tank for a closed heating system

The membrane expansion tank is designed to compensate for the thermal expansion of the coolant and maintain the required pressure in closed heating systems.

Liquids that are used in heating systems increase their volume when heated due to thermal expansion. For example, the volume of water when heated to 90 o C increases by 3.55%. If ethylene glycol-based antifreeze is used as a coolant in the heating system, the volume of the liquid increases even more.

Diaphragm expansion tank for heating. Device and operation scheme. Through the air valve (nipple), the air chamber is filled with compressed air using a car pump.

In a closed heating system without an expansion tank, even a slight increase in temperature will lead to a sharp increase in pressure and activation of the safety valve. Excessive coolant will flow out through the valve.

A membrane expansion tank for heating is a vessel divided into two parts by a movable membrane. One part of the vessel is connected to the heating system and filled with coolant. Air is pumped into another part of the vessel at a certain pressure.

When the volume of liquid in the heating system changes, the membrane in the tank moves in one direction or another. As a result, the volume occupied by the liquid in the tank also changes. The compressed air on the other side of the membrane acts as a spring, maintaining the operating pressure of the coolant and preventing the safety valve from operating.

Operating limitations and safety requirements

Depending on the design of the expansion tank and the materials used, manufacturers impose certain restrictions on their use in heating systems.

As a rule, manufacturers impose certain requirements on the composition and corrosive properties of the coolant fluid in the heating system. For example, they limit the content of ethylene glycol in an antifreeze solution.

It is prohibited to use the expansion tank at pressures exceeding the permissible values ​​specified in the manufacturer’s technical documentation. At the point where the expansion tank is connected to the heating system, it is necessary to install a safety group that monitors and limits the pressure in the tank.

In heating systems of private houses and autonomous heating of apartments, tanks and other heating equipment with an operating pressure of at least 3 are used. bar.

The expansion tank for heating is not allowed to be used in drinking water supply systems.

Installation, installation and connection of the expansion tank

The expansion tank is connected to the return pipeline of the heating system on the suction side of the circulation pump. 1 - membrane expansion tank; 2 - connecting shut-off valves and drain valve; 3 - circulation pump; 4 — make-up valve

The expansion tank is installed in a heated room. The tank is placed in a place that is easily accessible for maintenance. Installation is carried out in such a way that there is access to the air nipple, flange and connecting fittings.

Small expansion tanks are usually attached to the wall using a bracket. Fastening parts, as a rule, are not included in the product package and must be ordered separately. Large tanks are installed on the floor, on legs.

The expansion tank is connected to the return pipeline of the heating system on the suction side of the circulation pump.

The connecting fittings for the expansion tank allow you to disconnect the tank from the system, drain water from the tank, and seal the shut-off valve.

At the connection point, on the line to the tank, it is necessary to install shut-off valves that are protected from accidental closure. In addition, a drain valve should be installed to empty the tank. Manufacturers of tanks usually offer special connecting shut-off and drainage fittings for their products. These kits must be ordered separately.

To connect the tank to the return pipeline, pipes with an internal diameter equal to the diameter of the tank connecting pipe should be used.

The expansion tank is connected to the heating system after flushing the system.

The built-in membrane expansion tank is located on the rear wall of the double-circuit gas boiler

Membrane expansion tanks are sometimes built into boilers. For example, double-circuit gas boilers, as a rule, already have a built-in expansion tank of a certain capacity. If the volume of the built-in expansion tank turns out to be small for the heating system, then it is necessary to install a new tank outside in front of the boiler on the return pipeline. The volume of the new tank is selected as usual, without taking into account the capacity of the built-in tank.

Setting the pressure in the expansion tank

Before commissioning the heating system, before filling the tank with coolant, air is pumped into the expansion tank through the air valve - nipple using a car pump. The amount of air pressure is controlled by a car pressure gauge built into the pump or a separate device. Many manufacturers sell expansion tanks already filled with air or nitrogen to a certain pressure specified in the technical documentation. In any case, it is necessary to check that the initial air pressure in the tank is sufficient.

Initial pressure in the air chamber expansion tank - R o :

P o > P st + 0.2 bar ,

Where R st— the static pressure of the heating system at the location where the tank is installed is equal to the height of the water column from the expansion tank connection point to the top point of the heating system (column height 10 m = 1bar)

The initial pressure in the air chamber must be checked and adjusted when there is no liquid in the tank— open the connecting fitting and pour out the remaining coolant from the tank. The expansion tanks built into the boiler are also emptied of liquid.

In the heating system of a private house, it is convenient to install an expansion tank with the air chamber factory-filled with air or nitrogen pressure P o = 0.75 - 1.5 bar . This pressure value set at the factory can be left unchanged, even if it is significantly greater than calculated using the formula R o. In most cases, this pressure is quite sufficient for the heating systems of a private house or apartment.

The expansion tanks built into the boiler are usually already filled with air or nitrogen to the pressure specified in the boiler instructions. Before installing the boiler, it is necessary to check the air pressure in the expansion tank and, if necessary, adjust it - pump in or bleed air.

The initial pressure exceeds the static pressure by at least 0.2 bar. necessary to create pressure in the system, which reduces the risk of vacuum formation, vaporization and cavitation.

At the next stage the tank is connected to the heating system. Then the make-up valve opens and the heating system and tank are filled with coolant with the initial make-up pressure - R start.:

P start > or = P o + 0.3 bar

(for example, if P o = 1 bar, then P start >= 1.3 bar)

R o— initial pressure in the air chamber of the expansion tank.

Often, manufacturers of boilers, for example gas boilers, indicate in the technical documentation the recommended initial pressure for recharging the coolant in the system. The instructions also indicate the minimum coolant pressure, below which the boiler simply will not start working. In this case, fill the system with the initial pressure specified in the instructions for the boiler.

Further, turn on the boiler and heat the heating system to the maximum operating temperature (for example, 75 o C). When water is heated, air dissolved in it is released. We remove air from the heating system. We monitor the pressure gauge readings and record the pressure value in the system with expanded water - R ext.

In custody turn off the circulation pump and turn on the make-up again and bring the pressure in the system at the maximum temperature of the coolant to the final one - R con:

R con< или = Р кл — 0,5 bar ,

Where R cl— opening pressure of the safety valve of the heating system.

(for example, if R cl = 3 bar, then we bring the pressure in the system to P con<= 2,5 bar at coolant temperature 75 o C)

The method described above for adjusting the pressure of the expansion tank allows you to increase the effective usable volume of the expansion tank to the maximum. The tank will be able to absorb the largest amount of water, and then return it to the system.

This can be useful in the case of, for example, small leaks in the system. The tank will be able to release water into the system for a long time - the pressure in the system will decrease at a slower rate. The heating system will remain operational for a longer time. Or, as a result of cooling of the coolant, the pressure in the system may drop below the minimum required to turn on the boiler. In this case, the automation will not be able to start the heating. When adjusting the pressure according to the above method, the risk of such a development is reduced to a minimum.

These advantages of the pressure adjustment method described here are especially relevant for heating systems in country houses, where owners do not visit every day.

Checking membrane integrity

Operate the air valve (nipple) briefly. If water is leaking from the valve, the tank must be replaced, or, in tanks with a replaceable membrane, the membrane must be replaced.

If it is necessary to remove gas from the air chamber of the expansion tank, be sure to empty its water chamber first, and not vice versa!

Before refilling the tank with water, set the required pre-pressure in the air chamber. If these instructions are not followed, there is a risk of diaphragm rupture.

Calculation of the volume of the expansion tank for heating

The volume of the expansion tank is selected in such a way that when the coolant is heated to the maximum operating temperature, the increase in pressure in the heating system does not exceed the permissible value (remains below the response pressure of the safety valve).

Expansion tank volume for heating systems with a capacity of up to 150 liters

For heating systems containing a small amount of coolant, up to 150 liters, the volume of the expansion tank is selected using a simplified formula: ,

Vn = 10 - 12% x Vs Where: Vn — calculated volume of the expansion tank; V s

- full volume of the heating system.

Calculation of the capacity of the expansion tank for a heating system with a volume of over 150 liters The calculation begins with determining the increment in coolant volume - the additional volume that is formed as a result of heating the liquid to operating temperature -.

V e,

V e = V s x n% — calculated volume of the expansion tank; Where, — full volume of the heating system;— coefficient of expansion of the liquid in the heating system.

Expansion coefficient value — full volume of the heating system;, at the maximum operating temperature of the coolant (water) in the heating system, is determined from the table:

T oC	40	50	60	70	80	90	100
nv%	0,75	1,17	1,67	2,24	2,86	3,55	4,34

The expansion coefficient for antifreeze based on an aqueous solution of ethylene glycol (Tosol, etc.) is determined by the formula:

n a % = n v % x (1 + e a % / 100),

Where nv%— water expansion coefficient from the table above; e a %- percentage of ethylene glycol in the antifreeze solution.

At the second stage of calculation(second step) determine the volume of the water seal in the tank, Vv- this is the volume of coolant that initially fills the expansion tank under the influence of static pressure in the heating system. The water seal capacity is determined by the formula:

V v = V s x 0.5%, but not less than 3 liters.

At the third stage find the initial pressure in the heating system - P o. It is equal to the static pressure in the heating system and is determined from the calculation 1 bar= 10 meters of water column. The height of the water column in a heating system is equal to the vertical distance between the lowest and highest points of the system where the coolant is located. Using drawings or in situ, determine the vertical marks of the extreme points of the heating system. The difference between the upper and lower marks will be equal to the height of the water column of liquid in the system.

At the fourth stage calculations determine the maximum operating pressure in the heating system - P e. The maximum operating pressure must be less than the response pressure of the safety valve in the heating system by at least 0.5 bar.

P e = P k — (P k x 10%), but definitely P k - P e => 0.5 bar .

Vn = 10 - 12% x Vs Pk— response pressure of the safety valve.

At the conclusion of the calculation determine the required volume of the membrane expansion tank for heating using the formula:

V n = (V e + V v) x (P e + 1)/(P e - P o)

Choose a tank with a nominal volume greater than the calculated one.

Example of expansion tank calculation

Let's calculate the expansion tank for the heating system with the initial data:

Overall volume Vs = 270 l.

Water column height 6 m., hence the initial pressure P o = 6/10 = 0.6 bar.

Maximum operating temperature of coolant (water) 90 o C. Using the table we determine the expansion coefficient n% = 3.55%.

The safety valve is set to operate at pressure P k = 3 bar .

We make the calculation:

V e = 270 l. x 3.55% = 9.58 l.;

V v = 270 l. x 0.5% = 1.35 l., since 1.35< 3, то принимаем V v = 3 l. ;

P o = 0.6 bar. ;

P e = 3 bar. — (3 bar. x 10%) = 2.7 bar., since the condition P k - P e => 0.5 bar must be met, then we accept P e = 2.5bar.

Vn = (9.58 l. + 3 l.) x (2.5 bar. + 1) / (2,5 bar. — 0,6 bar.) = 23,18 l.

Result:

We accept for installation an expansion tank with a nominal volume of 24 liters.

In addition to the volume, when choosing a specific type of expansion tank, the maximum operating pressure must be taken into account, for which the tank is designed.

A well-installed and adjusted heating system will work reliably with rational consumption of energy resources. One of the main components on which the flawless operation of the boiler and circuit depends is the expansion tank.

The tank parameters are calculated taking into account the boiler power and coolant volume. The difference between the modifications is the size of the pipes and the maximum pressure.

Watch a video about the features of the expansion tank

The main function of the design is to dampen the increased fluid pressure in the system. If the system is not equipped with such a device, a water hammer may occur, as a result of which pipes will rupture or heating equipment will be destroyed.

Externally, the tank is a metal body with filling inside and a pipe going out for connection to the heating system.

Heating expansion tank device

The expansion tank device consists of the following elements:

Safety valve;

Membranes;

Safety valve;

Water chambers;

Gas chamber;

Branch pipe.

Depending on the type, the design configuration may vary.