The principle of operation of the expansion tank in the heating system. Calculation of volume, installation and operation features

A properly selected and connected expansion tank for closed-type heating plays an important role. It will protect the heating circuit and extend the operating life of the equipment. A closed, sealed container will eliminate the need to endlessly repair the system and change devices. It's worth getting to know her. Is it true?

We will tell you how to choose a closed expansion tank model in accordance with the technical data of the system. We'll show you how to install and connect it correctly. In addition, the article provides recommendations that must be followed to extend the life of the equipment.

Types of heating systems

There are two types of heating systems - closed and open. In a closed system, the coolant circulates in a closed circle (see figure below). When open, it enters the heating system, gives off heat and leaves it.

Central heating in multi-storey buildings is an example of an open type system. Hot water enters the building, which passes through the radiators and gives off its heat. After this, it returns to the boiler room, thermal station, etc.

Closed-type heating works according to the following scheme:

1. A heat source (boiler, heat pump, solar collector, etc.) heats the coolant;
2. The coolant enters the heating system;
3. Passing through heating devices (warm floors, radiators, fan coils), the coolant gives off heat and is cooled;
4. After passing through the heating system, the coolant returns to the heat source.

There are also systems with natural and forced circulation. In the first case, the coolant moves through the pipes due to natural convection. In the second, it is pumped through the system by a circulation pump.

Closed heating system. The coolant circulates in a closed loop from the boiler to the heating devices.

Where to put it in the system

The expansion tank in a closed system is placed after the boiler before the pump, that is, so that it creates a flow in the opposite direction. This way the system works more reliably. So the specific installation location depends on where you have the circulation pump.

Installation diagram of an expansion tank for heating

It is connected to the system via a tee. You cut a tee into the pipe, direct the perpendicular outlet upward, and screw the tank onto it. If the wall does not allow you to place a container, you will have to make an elbow, but the tank will be turned upward. Now we can assume that the expansion tank is installed.

Installation example with tap

But for the convenience of checking, it is advisable to install another tee after the tank, and install a shut-off valve on the free outlet of it. This makes it possible to check the membrane tank without draining the entire system - it cuts off the tank. Turn off the tap and bleed water from the boiler. Check the pressure on the disconnected branch (in the boiler). It must be zero. Afterwards, you can carry out all other setup work.

Why do you need an expansion tank?

In closed heating systems, the volume of the coolant varies depending on its temperature (see table). For example, if water is heated from +40°C to +85 degrees, its volume will increase by 2.5%. This may seem like a small value to you, but it is dangerous for the heating system!

The fact is that water or coolant is not compressed - it puts pressure on pipes, fittings, and heating devices. Even slight expansion can lead to leaks. To compensate for this, an expansion tank is used.

Water in central heating systems does not differ in quality; it may contain air. Over time, it accumulates in the upper points of radiators, which is why they heat the room worse.

In closed systems, the coolant may react with the heating system material. which causes gas to be released. Over time, some coolant components may also decompose, releasing air or other gases.

If ordinary water circulates through your closed system, it can also cause air locks. It may contain impurities that react with the material of pipes, fittings and heating devices.

The expansion tank serves as a kind of catcher and reservoir for air and gases. Once they get into it, they no longer return to the general system. Installing a tank helps protect against airing of the system and you will not need to bleed air from the heating radiators.

Calculation of tank volume

First of all, let’s determine the relationship between the required volume and the parameters that influence it. When making calculations, it must be taken into account that the larger the capacity of the heating system and the higher the maximum temperature of the coolant in it, the larger the tank should be. The higher the permissible pressure in the heating expansion tank, the lower it can be. Of course, the calculation method is quite complex, so it is better to consult a specialist. After all, a mistake in choosing an expansion tank can cause frequent operation of the safety valve or other troubles.

The volume is calculated using a special formula. Here the main quantity is the total volume of coolant that is present in the heating system. This value is calculated taking into account the power of the boiler, the number and types of heating devices. Approximate values: radiator – 10.5 l/kW, floor heating system – 17 l/kW, convector – 7 l/kW.

To make a more accurate calculation of a device such as a vacuum expander for heating, the formula is used: Tank volume = (Volume of water in the heating system * Expansion coefficient of the coolant) / Efficiency of the expansion tank. The expansion coefficient for water is 4% when it is heated to 95 degrees. To determine the efficiency of the tank, another formula is used: Tank efficiency = (Highest pressure in the system - Initial pressure in the air chamber) / (Highest pressure in the system + 1).

Expansion tank useful volume coefficients

Thus, the vacuum expansion heating tank is selected taking into account the strength and temperature characteristics, which should not exceed the permissible values ​​at the connection point. The volume of the tank can either be equal to or greater than the result obtained as a result of the calculations.

How does an open expansion tank work?

An open expansion tank is simply a container partially filled with coolant. Sometimes there is not even a valve for air to escape, but just a hole.

Open expansion tanks have two big disadvantages. First, they are susceptible to corrosion because they come into contact with open air. Secondly, they can only be installed in systems with natural circulation.

If you have a circulation pump installed that circulates coolant through the system, then it will not go further than the open expansion tank. The coolant will simply fill the tank and overflow.

Expansion tank in an open heating system

Specifics of the location of the open tank

The features of such a system are probably already clear based on its name. The circuit is, of course, closed, but it is not isolated from the atmosphere, it is not sealed, and by definition there cannot be excess pressure in it. And the expansion tank is a regular container embedded in the circuit. The main condition is that it must be located above the highest point of the system.

Prices for expansion tanks

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 can transform into its usual gaseous state. In addition, chemical reactions between the coolant and the material of pipes and heat exchangers can also lead to the release of gases. And the accumulation of gas can block the radiator or even an entire section of the heating circuit. So timely removal of gas bubbles is an extremely important task.

True, sometimes open expansion tanks crash into the return line (for one or another layout considerations). But still, this is the highest point of the system, to which a vertical pipe is simply laid. In this case, the gas vent 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 or have certain improvements. In any case, this is a container of a certain volume, which is usually covered with a lid on top. The lid is needed solely to protect against debris or dust getting into the water, and is never airtight. That is, the current atmospheric pressure is always maintained in the tank. And the container itself has pipes embedded in it - from one in the simplest design to several for different purposes.

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

But many craftsmen prefer to make such tanks themselves. The container can be welded 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 little, and making the appropriate insertion of the pipes will also not be difficult for a good owner.

Let's look at several possible schemes for such tanks:

The simplest scheme is that a pipe is simply cut into the container from below, which is connected to the heating circuit.

It is clear that with this design there will be no circulation of coolant through the tank. When filling the system, ensure that the water level in the tank is located 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 necessary over the level of coolant in the tank - evaporation, one way or another, will happen, and if you do not replenish the water, you can cause air blockage in the system circuit or “airing” of the radiators. So you will have to look into an expansion tank of such a simple design regularly to recharge if necessary.

To facilitate visual control, various tricks are used. In particular, you can embed a small diameter pipe into the side of the tank, onto which a short piece of transparent hose is placed. It is clear that the water level in the hose will correspond to the level in the tank - a fleeting 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 this place becomes the attic. That is, the container is not located in plain sight, and climbing up every time to check the level is extremely inconvenient. But this control can be organized in another way. An example is shown in the diagram below:

There are two pipes cut into the tank from the end side.

— The upper one (item 1) determines the maximum permissible filling of the container, and simply works for overflow. A pipe (hose) is led from it into the sewer system or even simply discharged onto the ground - into the garden.

— A pipe leading into the room is connected to the lower branch pipe (item 2), on which a regular ball valve is placed in a place convenient for the owners. The height of the embedded pipe determines the minimum permissible water level in the tank. That is, to control the filling, you just need to open the tap slightly - if water comes out of the pipe, then everything is normal. Otherwise, replenishment 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, 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 connect a make-up pipe to the tank (from the water supply), but connect it through a float valve, which is usually used in toilet flush tanks.

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

All the schemes shown above can be figuratively called “passive” - no coolant circulates through the expansion tank. This simply creates free space for the expanding volume of liquid. It's easy and quite workable. But there is also a drawback - the function of the air vent in such tanks is very unproductive. A considerable number of air bubbles, carried away by the flow of water when following the supply line, will simply slip past the insertion point of the pipe leading 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 circuit.

It might look something like this:

The coolant is supplied to the tank through pipe 1 , and through pipe 2 it again enters the supply line. A sharp increase in volume (at the transition from the diameter of the pipe to the tank) correspondingly causes a sharp decrease in the flow rate, which contributes to the ascent and release of the smallest gas bubbles into the atmosphere. The position of pipe 1 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 (item 3) and make-up in such schemes are no different from the options shown above. It’s just that not everything is indicated here, so as not to overload the drawing.

Of course, if such a scheme for connecting an expansion tank is used, then steps are taken to ensure 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 may have further development. You can find examples where the expansion tank is also assigned the function of a distribution manifold 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 from it, through the embedded pipes, the hot coolant is distributed along the risers of the system.

What tank volume will be required?

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

Based on the above values, one could assume that since heating 100 liters of water to 90 degrees gives an increase in volume of 3.5 liters (that is, essentially 3.5%), then we 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 that will compensate for the expansion. Approximately at the upper boundary of this volume, an overflow pipe is inserted. Well, there must be free space above the water level up to the lid. That is, there is no way you can meet 5 percent.

The experience of heating installers shows that the optimal solution would be based on the following approximate ratio: tank volume ≈ 10% of the system volume .

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

• If the heating system is ready, then the easiest way will be to measure with a water meter how much will fit into it before it is completely filled. The technique is very accurate, but rarely helps. Agree, usually the tank capacity is calculated in advance, and not after installing the circuits.
• With a very large error, but you can still accept the ratio: 15 liters of water for every kilowatt of boiler power . It is clear that with this approach it is not difficult to make a mistake.
• Finally, the volume of the heating system can be simply calculated. It must be assumed that if you plan to install an expansion tank, then the system design already outlines the installed contours of pipes of one type or another and diameter, and the boiler model, 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 reality it’s not so scary - if you use our online calculator, to which the link leads (it will open on a separate page).

Prices for expansion tanks GILEX

How to calculate the total volume of the heating system?

Selecting an expansion tank is far from the only case when this parameter becomes necessary. For example, this is required when purchasing antifreeze coolant, when carrying out some calculations of mixing units, etc. Using our calculator for calculating the total volume of the heating system, the reader will perform the calculations without any problems.

Please note that if calculations are made to determine the optimal volume of the expansion tank, then the tank itself should be excluded from the calculations. This is 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.

Such systems, by the way, were completely dominant not so long ago. If only for the reason that it was simply impossible to buy equipment for a closed type system. But today, unfortunately, they have to be considered obsolete.

• A clear advantage is the simplicity of the design. In some cases, there is practically no need to purchase any additional materials at all. If desired, a fully functional tank can be made “on the knee” from “trash” stored in the garage.
• A priori, dangerous pressure cannot arise in an open system, since it is connected to the atmosphere. This eliminates the need for a safety valve.
• Let's add to the advantages the ability of the expansion tank to act as an air vent.

But disadvantages :

• It has been noted more than once that the tank should be installed at the highest point of the system. It’s good if the house has an insulated attic. But this does not always happen, and it is necessary to provide very high-quality insulation of the container so that it simply does not “get caught” in 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 requires constant monitoring. This problem, as we have seen, can be solved, but still.
• Not only that, due to leakage, 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 noticed, the discussion above was exclusively about water as a coolant. In open systems, it cannot be otherwise - evaporation of expensive antifreeze looks like waste. 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 operation is based on the principle of electrical conductivity of the coolant, that is, the chemical composition is important. And with uncontrolled evaporation, the optimal concentration will quickly be lost.
• Stable low system pressure is not always an advantage. Some heating devices, on the contrary, show their advantages precisely at elevated pressure levels.

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

Operating principle of a closed (membrane) expansion tank

The design of a closed expansion tank differs from a closed one in the presence of a membrane. It is impermeable to air and coolant and divides the container into two parts.

The operating principle of a membrane expansion tank is simple. When the coolant heats up, it increases in volume. Under pressure, the membrane rises. This increases the total volume of the heating system and does not put additional pressure on it.

When cooled below a set temperature, the coolant contracts. The membrane lowers and the volume of the heating system decreases. This compensates for the vacuum created by compression of the coolant.

Advantages and disadvantages of an open heating system

This scheme is still used to heat private houses and cottages. Hot water from the boiler, according to the laws of thermodynamics, without a pump, rises up the riser, and then spreads along the supply lines located with a slope of 0.5 cm/m. At the same time, it fills the radiators. The liquid then flows by gravity back into the boiler or boiler to be reheated.

Main elements of an open heating system:

1. Boiler
   - in an open circuit, gas and solid fuel boilers of single- and double-circuit types are used.
2. Radiators
   - the pressure in an open heating system is low, so any battery model is connected to it. Aluminum heaters work efficiently, heat up quickly and release heat intensively. You can install bimetallic radiators with an aluminum body and a steel water-conducting part. Traditional cast iron options also serve reliably.
3. Pipes
   - in modern houses, models with a diameter of 25–50 mm made of heat-resistant polymer are used. Pipes of the maximum size are installed at the outlet of the boiler, and minimum size at the outlet. This allows you to maintain the required pressure and proper fluid circulation.
4. An open-type expansion tank -
   you can buy it in a specialized store, order it online, or make it yourself.
5. Shut-off valves
   - installed on the riser and collectors for emergency shut-off of water.
6. Control taps and automatic thermal heads
   are additionally mounted on batteries to adjust the temperature.
7. For Mayevsky's wounds
   there are air vents necessary for releasing air and preventing air locks. Installed on radiator housings.

Advantages of an open system:

1. Energy independence
   - this circuit works without a pump, so it is not afraid of power outages. If there is a power outage, the water and pipes will not cool down.
2. Budget-friendly
   - no pumping equipment is required for operation; you can weld the tank yourself, buy it inexpensively, or adapt an ordinary canister.
3. Easy to use
   - owners only need to monitor the condition of its elements and add water.

Flaws:

• The complexity of calculations and installation - when installing collectors, it is important to maintain the required angle - even small errors will lead to stagnation of water and poor heating of the batteries.
• Impossibility of use in buildings with irregular occupancy - non-freezing liquid cannot be poured into such a heating system. When it comes into contact with air in the tank, it evaporates and loses its properties.
• Difficult to operate in houses with a large area and number of floors - for such buildings, a closed heating system is preferable, which is able to warm up a building of any size.

However, despite the disadvantages, an open heating circuit is appropriate in small houses with permanent residence. Therefore, she does not lose her popularity.

Membrane tank design

The design of a closed expansion tank is very simple. At the top there is a nipple through which air is pumped into the chamber. It is necessary to balance the pressure inside the container.

There is a rubber or polyurethane membrane located right in the middle of the tank. It is sealed and does not allow air or coolant to pass through. The membrane divides the tank into two parts. The lower chamber is designed for coolant, which gets there due to heating and pressure expansion. The upper one is for air under pressure, which prevents the coolant from immediately filling the entire cavity.

The internal structure of the expansion tank is membrane (closed) type.

Useful tips

It was already mentioned above that the volume of the expansion tank is equal to 10% of the volume of the entire coolant in the heating system of the house. Of course, this is an approximate figure. To accurately determine it, it is necessary to take into account a large number of various coefficients that are included in a complex formula. It will be difficult to make such a calculation on your own, if you are not a specialist. Therefore, take the above ratio as a basis.

By the way, if the safety valve trips very often, you know that you missed the volume. Most likely, you incorrectly calculated the total volume of coolant. In this case, do not rush to replace the installed expansion tank with a new one with a larger volume. You can simply insert another one next to it so that it compensates for the missing liters.

When the question arises of how to install the piping of the expansion tank, there are only two points to consider:

1. The coolant must enter it from the top point.
2. And leave from the very bottom.

Expansion tanks of open and closed type

This is how you can avoid mixing air with water inside the tank.

Very often, ordinary people ask why the expansion tank is boiling? There are two reasons:

• The diameter of the contour pipe is incorrectly selected. Usually a reduced diameter leads to boiling, so experts advise using pipes of at least 32 mm. But also take into account the fact of correct installation of heating radiators. They should not rupture the pipe system, but crash into it.
• Lack of slope of the contours, which we have already discussed above. Therefore, you will have to redo the heating system or install a circulation pump in it.

A few words about the pump. It was already mentioned above that open-type heating and a circulation pump are not always compatible. If you increase the volume of coolant, then a low-power pump can be inserted into the circuit. And this will solve the problem. By the way, they install it on the return circuit near the boiler. How to increase the volume of coolant? Option one is to increase the diameter of the distribution pipes. You can also increase the sections of heating radiators. In general, everything will need to be calculated and thought through. You shouldn't make hasty decisions.

Air pressure in the tank

The water or coolant in the heating system is always under pressure. In private houses it is 1.6-2 atm., in multi-storey houses - many times more. To ensure that the coolant does not lose pressure during normal operation, the upper part of the expansion membrane tank must be filled with air.

The air pressure in the upper chamber should be 0.2 atm. lower than the coolant pressure in the system. A regular bicycle or car pump is suitable for pumping air. The only thing you may need is an adapter.

At the top of the expansion tank there is a nipple with a spool. The operating principle is the same as in car or bicycle wheels. To deflate the air, just press the small tongue inside it.

Some manufacturers fill the tank not with air, but with nitrogen. In fact, this will not change the effectiveness of its work at all. This is an advertising ploy - they are trying to force you to buy more expensive equipment.

Purpose of closed tanks

All of them, regardless of volume and performance, are designed to level out the expansion of the coolant (special liquids, water), which occurs when its temperature increases.

This is done in order to avoid destructive water hammer, damage to fittings, fittings, rupture of heating system pipes, and extrusion of gaskets.

Any closed tank is a sealed steel tank, divided into parts by an elastic membrane, which changes its position as the temperature of the coolant increases/decreases

Example: the coolant (water) expands by four percent as the temperature rises to 95 °C. Which is quite enough for the engineering system to fail.

Expanzomat design and components

Any such modern product consists of the following structural elements:

• housings;
• coolant chambers;
• a gas chamber into which ordinary air or inert gas is pumped;
• membranes.

The option of filling the gas chamber with inert gas is more preferable, because it provides the container with greater durability. But regular air is more accessible.

The membrane is made of elastic materials, therefore it is able to change its position as the temperature of the coolant increases or decreases. This structural element can be of the diaphragm or balloon type, and their operating principle is similar.

The tanks are connected to the heating system using a special pipe. A valve is provided for pumping gas. Closed-type containers are manufactured in a horizontal or vertical layout, which makes it easier to complete the heating system.

Modern expansion tanks intended for use in heating systems come in various sizes, shapes, and their performance characteristics are radically different. All of the above allows you to make the best choice in any situation.

Tanks intended for installation in closed heating systems are equipped with pressure gauges to monitor internal pressure. Similar products intended for installation in systems of ordinary private houses operate at low loads not exceeding 3.5-4 bar, so they do not require measuring instruments.

You can also find two types of tanks on sale:

• with a non-replaceable or stationary diaphragm-type membrane, that is, a break, the wear of which will lead to the replacement of the entire device;
• with a replaceable balloon-type membrane.

In the first case, the products are distinguished by a more affordable price, in the second by greater functionality, maintainability and durability.

The design of flanged tanks allows you to replace a worn or damaged membrane, and in some cases you can even do this yourself. And replaceable membranes can withstand greater pressure.

Expansion tank operation diagram

When the coolant is cold, the tank membrane occupies as much space as possible. As the temperature rises, the pressure on it increases.

As a result, the specified structural element overcomes the resistance of the inert gas or air and changes its position, freeing up more space for the resulting excess liquid.

Expansion tanks are not involved in the process of heating rooms, but their task is more than important. Since each such product prevents breakdowns of the heating system, which can occur due to water hammer and increased coolant pressure

When the coolant cools down, the opposite process occurs to that described above. And then the cycles are repeated many times.

Calculation of the expansion tank using the formula

If you do not want to go into details, you can install a tank with a capacity of 10% of the total coolant volume. But sometimes it’s better to calculate everything exactly. By equipping a large heating system, you can save a lot.

To calculate the required volume of the expansion tank, you need to know the following:

• Minimum coolant temperature;
• Maximum coolant temperature;
• Heating system volume;
• The percentage of ethylene glycol or propylene glycol in the coolant.

Important!

If you are going to heat a house or cottage where you do not live permanently, be careful when selecting the type of coolant. They have different freezing temperatures and expansion coefficients.

To calculate the volume of the expansion tank you need to use the formula:

V = V1 x ( Q – Q1)

In this formula:

• Q1 – expansion coefficient at minimum temperature (see tables below);
• Q – expansion coefficient at minimum temperature (see tables below);
• V1 – volume of coolant in the heating system in liters;
• V – volume of the expansion tank in liters.

If an expansion tank is already installed in the heat source, then it must be taken into account. To do this, subtract the built-in capacity from the obtained “V” value. The resulting number is the required volume of your expansion tank.

Important!

If you have a forced circulation heating system, the minimum total capacity of the expansion tank is 15 liters.

Thermal expansion coefficient of ethylene glycol solution

Volume expansion coefficient of propylene glycol

In order to determine the amount of coolant in the heating system, you need to take into account the volume:

• Connected devices (radiators, underfloor heating, etc.);
• Pipes;
• Collector (comb);
• Heat source (for example, how much coolant is in the boiler or boiler coil).

The volume of pipes can be calculated using the formula:

V = L x 0.0785 x D x D

In this formula:

• L – heating pipe length;
• D – diameter in cm;
• V is the volume of coolant in the pipe in liters.

You can see the volume of coolant in the batteries in the specifications or instructions for them. If there are none, you can find out the amount of coolant in the publication “The volume of water in a heating radiator - aluminum, cast iron, bimetallic.”

Recommendations for choosing a container

The most important feature that you should pay attention to when choosing an expansion tank model is the volume of its tank. For closed systems with a small circuit, the volume of coolant in which does not exceed 150 liters, the capacity is easy to calculate.

So, it should be:

• when using water as a coolant - 10% of the volume of the entire heating system (for example, if this figure is 100 liters, then the expansion tank must hold at least 10 liters);
• when using glycol liquid as a coolant - 15% of the volume of the heating system.

In the latter case, the capacity should be larger due to the greater expansion coefficient of the specified antifreeze.

The advantage of modern expansion tanks is the reaction of their membrane to any change in coolant temperature. Which guarantees safety of use. But it should be remembered that tanks are designed to operate in certain conditions, so they must be selected correctly

The volume of the tank for larger systems, the circuit of which circulates more than 150 liters, is most conveniently calculated using the parameter of the total volume of the system and a table for selecting a tank.

To calculate the total volume of the system, you can use the following methods:

1. Measure the volume of coolant circulating in all individual elements of the system (boiler, radiators, pipelines) and then sum up the results obtained. This method is highly labor intensive, but at the same time it is the most accurate.
2. Multiply each kilowatt of boiler power by 15, assuming that on average there are about 15 liters of coolant per 1 kW. This method is simple, but you should remember that you can trust the result only when you are confident in the correct selection of the heating element for the system.
3. Drain all water from the system and refill it, calculating the required displacement.

You can also use formulas or an online calculator to calculate the required tank volume. Why is it necessary to know the volume of coolant, its temperature and pressure in the system.

The method with formulas is more complex and the volume obtained as a result of calculations will not differ significantly from the rough calculation given above. Moreover, the found value must be rounded up.

Many manufacturers of expansion tanks offer the consumer assistance in selecting the right tank. To do this, tables are provided to make selection easier. However, they must indicate that the information provided is advisory in nature and the buyer bears responsibility in any case.

The most practical solution when choosing will be an expansion tank designed for closed-type heating systems, equipped with a safety valve.

The reason is that when the pressure rises to critical standards, the device will start working and bleed it. That is, this valve can significantly increase the safety of the entire heating system.

When purchasing a container, you should take into account that red paint is most often used to mark expansion tanks used for heating.

This feature will help to distinguish the desired product from other similar ones, for example, water supply tanks of similar size and shape - hydraulic accumulators, which are predominantly coated with blue enamel.

But if necessary, you can find tanks of various colors, which will help you place the one you need in any room without compromising its aesthetic qualities.

Containers can be horizontal or vertical, and manufacturers also provide the opportunity to mount them in different places. For this product, they are equipped with various accessories. And when purchasing, you should pay attention to this, determining the best option in advance.

When choosing, you should also pay attention to the quality of the materials used in the production of the container body and membrane. And the presence of a guarantee for the purchased equipment and instructions for installing and connecting it to the system.

Features of choice

It may seem to you that the expansion tank has a simple design and you can choose it only based on volume. But there are a few more points to consider:

1. The membrane material must be resistant to reagents and additives used in coolants;
2. The inside of the tank must be covered with high-quality paint or other coating.
3. The protective coating on the inside of the container should not react with the coolant;
4. The membrane must be resistant to high temperatures;
5. The maximum permissible pressure in the tank must correspond to the characteristics of your heating system;
6. All connections and seams must be resistant to high pressure and water hammer.

How to install?

There are no significant restrictions affecting the installation location of the expansion tank in the system. Nevertheless, it is advisable to carry out the installation at any convenient point in the return line of the existing heating system.

The reason is that the coolant there is cooler. And this allows you to significantly extend the life of the expansion tank and its membrane.

In addition, if you install the tank near a solid fuel boiler, then in certain situations steam may enter the coolant chamber. As a result, the container will lose the ability to compensate for the expansion of the coolant.

Installation of the tank can be done in two ways. These include installation:

• on the wall;
• on the floor.

But it should be understood that the first option is intended only for cases where the expansion tank has a moderate volume.

Tanks should be installed as far as possible from boilers. And the optimal solution would be to locate it in the return line. Since the coolant temperature there is noticeably lower, which eliminates premature failure of the membrane

You should not skimp on connecting the tank to the heating system.

So this procedure should be performed using:

• a shut-off valve with a so-called “American” - this design element will allow you to quickly remove the tank from service and, if necessary, replace it, without waiting for the coolant to cool down;
• a tee with a drain tap, which will allow you to quickly empty it before replacing the tank;
• pressure gauge for measuring pressure;
• safety valve or nipple to regulate the pressure inside the equipment.

After installing the tank, it must be configured correctly, taking into account the manufacturer’s recommendations given in the instructions for the purchased equipment. So that the pressure in the tank is appropriate, i.e. less than in the system, which will allow the membrane to deform when the coolant heats up.

If the calculations were carried out incorrectly and the heating system contains a tank of a smaller volume than required, then it will not cope with its duties, but the error can be corrected.

Why do you need to purchase and install a second container in the system? The capacity of which is the difference between the required volume and that available in the tank operating in the system. This method will reduce financial losses.

Installation location

An important position is the installation location. Since we are talking about an open type heating system, it is necessary to determine why it has such a name.

• Open.
• Closed.

We are interested in the open one. The name speaks for itself. In this case, the coolant at one of the points in the circuit comes into contact with the outside air. And this point is nothing more than an expansion tank. Its design has a top cover through which the coolant comes into contact with the air.

Installing a tank in a heating system

• Firstly, it is necessary to take into account the single-level arrangement of all radiators. That is, they should all be located at the same level without height differences.
• Secondly, there is a slight slope of the supply and return circuits. The first one slopes away from the boiler, the second towards it. This allows the coolant to move freely in a natural direction and correctly remove air upward.
• Thirdly, the expansion tank cuts into the supply circuit at the riser, which leads from the heating boiler to the upper pipe distribution. This is the best place, because the main accumulation of air is in the radiators.

Sometimes it happens that a so-called pocket forms in a pipe heating system. This is very rare, depending on the architectural features of the building. So, air in large quantities will certainly collect in this pocket, and it must be vented somehow.

Experts suggest installing another additional expansion tank here. It will be smaller in volume than the main one

It is only important to correctly select the dimensions of the device and build a heat exchanger drain. If the pocket is not very large, then you can do without a tank

Then a regular air vent is installed in the pipe on the downstream side.

Requirements and recommendations for installing a membrane tank

Small volume tanks are mounted on the wall.
You can install the equipment yourself, following the instructions. When working, adhere to the installation requirements:

1. The first stage is choosing a location. It is necessary to ensure free access to the tank for maintenance. A good place is considered to be the section of the return line between the pump and the boiler.
2. To ensure the safety of a closed circuit, you will need to install a safety valve, an air vent, a pressure gauge and a thermometer.
3. A drain valve is installed in front of the inlet pipe to drain water from the tank.
4. Filters must not be installed in the area connecting the tank and the heating system.
5. Before connecting the equipment, check the pressure of the gas space. If necessary, pump up air.
6. The tank should not be located in a room with sub-zero temperatures.

The tank is securely mounted on the wall, and no additional load should be placed on it. Large volume models are mounted on the floor. A connection diagram with the inlet pipe located at the bottom is recommended. Experts advise making a detachable connection between the pipe and the drain valve in front of it. If necessary, the expansion tank can be easily dismantled.

The manufacturer specifies the requirements for the amount of antifreeze in the coolant. The stated proportions must not be exceeded.

Possible breakdowns

With prolonged use, the membrane may burst.
During operation of the equipment, owners are advised to inspect the housing for leaks and damage every six months. It is also necessary to measure the pressure in the gas chamber. The condition of the membrane is checked once every 2 years. If there is no use for a long time, the water is drained from the tank.

Common faults:

• Pressure drop in the gas compartment - it is necessary to pump air through the nipple using a pump.
• Damage to the housing - mechanical stress or corrosion can cause a crack to appear. The seal of the container can be restored at a service center.
• Leaking from the air valve - due to high loads and hot water, the rubber may crack. It is better to replace the damaged part in a timely manner.

You can repair the equipment yourself. To replace the membrane, you will need to drain the water, remove the container and relieve the pressure. Then unscrew the flange bolts holding the rubber part. The old membrane is removed and replaced with a new one. All procedures are carried out in reverse order.