Principle of operation of a closed expansion tank

Comprehending the fundamentals of heating systems is essential for maintaining a comfortable and warm atmosphere in our homes. A crucial element that is frequently disregarded is the closed expansion tank. It might not be the most glamorous component of your heating system, but it’s essential to making sure your system runs well.

Think of your heating system as a well-tuned orchestra, where every instrument contributes to the overall harmony. Comparable to a conductor, the closed expansion tank quietly directs the operation behind the scenes. Its main job is to control the heating fluid’s expansion and contraction during the heating and cooling processes.

How then does this humble tank perform its magic? Imagine a balloon that, when inflated and deflated, grows and contracts. With a slight variation, the closed expansion tank functions using a similar principle. It has a cushion of inert gas, like nitrogen, in place of air, and a flexible diaphragm keeps the inert gas and heating fluid apart.

As the heating fluid heats up, it expands, increasing pressure within the system. This pressure buildup without the expansion tank could cause leaks, bursts, or even damage to your boiler. But because of the expansion tank, which keeps the gas compressed and stops pressure spikes, extra fluid is forced into the tank.

Installation of the expansion tank in the heating system of open and closed type

In contemporary heating systems, open or closed expansion tanks are used to counteract the coolant’s thermal expansion. These tanks come with specific installation and operating conditions requirements, as well as a range of benefits and drawbacks.

The primary considerations for choosing and installing an expansion tank in a forced or naturally occurring coolant circulation heating system will be covered in this article.

The tank’s useful volume is its primary parameter, and it needs to be greater than the value of the system liquid’s volume change due to the largest possible temperature change.

Because the coolant in the heating system can expand and contract while it is operating, the volume of liquid in the system is not constant. The heating of the coolant and the resulting expansion of its volume within the heating system’s internal space at a constant size increase pressure on the walls of the pipelines and heating equipment, potentially resulting in their destruction.

An expansion tank—also called an expanzomat, from the English word "expanse"—is incorporated into the heating system’s design to balance out variations in liquid volume and maintain pressure on the internal walls of the component parts. (See "expanse," a verb meaning "to expand"). The coolant expands and fills the expander with the excess that rises above the system’s internal volume. The expander then receives the returned coolant when the temperature falls.

How to determine the required volume of the expander?

The maximum volume of coolant that can enter the tank as a result of the tank heating up must be greater than the required volume of the expander.

The entire volume of coolant in the system is first calculated. The total volume of the system can be obtained by adding the internal volumes of all the pipes and cavities in the boiler, heating batteries, and shut-off valves. Using the information in Table 1, one can determine the volume of liquid in the pipes based on the pipe size. The product’s documentation (passport or manufacturer’s catalog) contains information on the equipment cavities’ volume.

Calculating the coolant volume in a single linear meter of the pipeline (Table 1).

Next, using the information in Table 2, calculate the volume of the expander that is needed given the total amount of liquid. The system pressure is taken into consideration when selecting this value. The larger of the two values in the table determines the required tank volume if the previously calculated value falls between them.

Calculating the expansion tank’s necessary volume is shown in Table 2.

If water is utilized as a heat carrier, then the data in Table 2 above are accurate. The table value of the total volume is multiplied by a correction factor equal to the ratio of the densities of the used liquid and water for liquids with thermal expansion coefficients other than water.

The main varieties of tanks

In a heating system, expanders come in two main varieties:

Single-volume expansion tanks of the open type are in communication with the atmosphere. In order to guarantee the liquid in the pipeline returns naturally when its temperature drops, a tank of this type must be installed at the system’s highest point.

Expander of the open type.

Closed expansion tanks are constructed as a sealed vessel with a portion filled with liquid and a portion filled under a specific pressure with gas or air. The gas is compressed when heated liquid enters the expansion chamber. The liquid returns to the system as it cools, and gas fills the volume difference.

Closed expansion reservoir.

Open-type expansion tank

Apart from its primary purposes of pressure stabilization and volume compensation, an open-type expansomator also functions as a vent for excess air in the system and as a source of water replenishment in the event of a minor leak.

Shaped like a rectangle or cylinder, open expansion tanks are composed of polymeric materials or sheet steel. The heating system’s upper point is where an open-type expansion tank is installed, necessitating an extension of the heating pipelines’ overall length. The coolant in the tank is shielded from impurities by the lid, which also allows access to the interior for maintenance.

The forced circulation system’s open expansion tank’s operation principle and connection diagram.

An open expansion tank can be placed in an attic room, a stairwell, or a specially designed box that is fixed to the house’s roof. The expander may be positioned in the utility room or bathroom if the building’s height permits installation inside the living space. Insulating tanks outside of the house’s heated area will help the system lose less heat.

Sheet metal is welded into an open tank.

Principle of operation and peculiarities of installation

The circulation of the water in the open-type tank must be ensured in order to prevent stagnation. To achieve this, a circuit with an expansion and circulation pipe installed between it and the main heating main—the latter’s opening situated about 50 mm lower in the tank—is placed between the two. If the system uses forced circulation, the circuit must be tapped prior to the pump’s inlet and installed on the return line in order for water to circulate effectively. Air bubbles can be released into the atmosphere from the system through circulation.

Expander of the open type featuring upper and lower level relays.

It should be mentioned that the aforementioned is accurate when adding an expander to a heating system that uses forced coolant circulation!

The expander in a naturally circulating system is connected at the top of the supply pipe to permit unrestricted air bubble escape.

At the lowest level of the tank, a control pipe emerges, and at the highest level, an overflow pipe that is used to empty the excess liquid exits. All it takes to check the level is to open the control pipe’s tap. The presence of water flowing from the tap indicates that the tank’s level is higher than the minimum. For this purpose, it is possible to install lower and upper level relays, which, in the event that the water level falls below the minimum value or approaches the overflow point, will sound an alert or illuminate.

The area of the expander’s base multiplied by the height between the lowest and highest level, or the increase in water volume due to thermal expansion, is the expander’s usable volume. It needs to be at least as much as the necessary sum, which is determined by utilizing Tables 1 and 2.

Advantages and disadvantages

The primary benefits of an expansion tank that is open-type:

1. simplicity of construction, which implies relatively low cost;
2. performs the function of pressure relief and venting from the heating system.

Open expansion tanks’ drawbacks

1. special conditions of installation, providing for the installation of additional pipelines;
2. high heat losses and the need for thermal insulation;
3. direct contact with the atmosphere, which may cause corrosion of steel elements of the system;
4. due to the possibility of vaporization, the system needs periodic replenishment of the coolant.

It is noteworthy that open-type tanks are becoming less and less common in residential heating systems due to the aforementioned drawbacks, with closed expanders becoming more and more popular in their place.

Closed type expansion tank

The closed expansion tank is isolated from the atmosphere, in contrast to open expansion tanks. The tank is a sealed steel vessel that is pumped with inert gas through a special valve and partially filled with liquid. Closed tanks are classified into the following categories based on how the internal volume was separated:

Closed expanders in a range of dimensions.

membraneless

Since the internal space of diaphragmless expanders is not mechanically separated, the coolant and gas are in direct contact. The outside gas cylinder or compressor is used to keep the pressure at a certain level. Gas supply and pressure control are automated.

During a period when rubber (rubber) diaphragms had a short lifespan and needed to be replaced frequently, diaphragmless tanks were widely utilized. They didn’t need a diaphragm to function, but the design was made more difficult by the requirement for a compressor or cylinder. These days, separating membrane-equipped closed tanks are frequently utilized.

Membrane

Liquid and gas are kept apart in contemporary expander designs by a flexible diaphragm. Some expanders come equipped with:

1. plate diaphragm (diaphragm);
2. pear-shaped (balloon) diaphragm.

The disk-shaped one, which resembles a hemisphere, is positioned in the center of the tank. It takes on either a convex or concave shape depending on the temperature of the water.

Design of a diaphragm-equipped expander.

The diaphragm, which has a pear shape, is fixed on opposite ends of the vessel and conforms to its shape. These tanks are unique in that the flexible diaphragm fills with liquid and gas is pumped between it and the metal walls, preventing the coolant from coming into contact with the walls. This prolongs the structure’s service life and prevents corrosion. While diaphragm tanks are designed to prevent it, this design permits diaphragm replacement.

Diaphragm tank with a pear shape.

Butyl and ethylene propylene diaphragms, which are known for their increased durability, are used in modern expanders. Rubber, which has a shorter lifespan and is no longer used, was once used for this purpose.

Tank operation schematic with compressor included.

Advantages and disadvantages of membrane tanks

The following are membrane expanders’ drawbacks:

• high cost;
• the need for periodic pumping of gas or air;
• the need to control the pressure in the system.

Among the benefits are:

• compact dimensions;
• minimal heat losses, no need for thermal insulation;
• absence of direct contact of the heat transfer medium with the atmosphere (vaporization), which reduces the risk of formation and spread of corrosion and the need to recharge the system;
• ability to work at high pressure;
• possibility of installation practically in any place.

Choosing a diaphragm expander

The essential liquid volume in the system is the membrane tank’s primary parameter, and it should be pre-calculated using Tables 1 and 2. The volume of the tank needs to match or exceed the calculated value.

Flat diaphragm expanders are produced by numerous manufacturers in addition to the conventional oval shape. This type of tank is smaller and can be mounted in the gap between the wall and the room’s interior without taking up any valuable space.

Expander with a flat shape.

The diaphragm is the primary component of a modern closed-type tank, and its manufacturing quality and parameters define how long it will last. The membrane’s primary attributes are:

• range of operating temperatures and pressures;
• material;
• diffusion resistance.

Red membrane tanks are used in heating systems, and blue membrane tanks are used in water supply systems. The hygienic standards for heating system expanders’ diaphragms are less strict.

Rules for installation of closed expansion tanks

A heating expander was installed.

1. Installation of a closed expansion tank in the heating system can be carried out at any point in the circuit, but the optimal installation is before the circulation pump (for heating systems with forced circulation of the coolant).
2. It can be installed in any position, but the top-fed version is preferable because it allows air bubbles to escape naturally. This installation will ensure that the tank is operational even if the diaphragm ruptures.
3. If during the operation of the heating system it is found out that the volume of the installed tank is not enough, instead of replacing it, it is more rational to install an additional tank of the required size.
4. When changing from water to another heat transfer medium, it may be necessary to replace the expansion tank with a larger one. Installation of an additional expansion tank is possible.
5. Some models of heating boilers have a built-in expansion tank, in which case installation of an additional one is not required.
6. Installation of a closed expander in a heating system with natural circulation requires installation of an "auto-resetter" (automatic float valve) in the upper point of the system for automatic venting of air when the system is filled and during the boiler operation.

Expansion tank operation

Keeping the diaphragm-style expansion tank in operational order entails:

1. Regular visual inspection for the absence of corrosion;
2. Checking the integrity of the diaphragm;
3. Checking the air (gas) pressure.

When maintaining open-type tanks, it’s important to check the insulation and body from the outside and make sure the liquid level doesn’t drop below the minimum mark.

An expansion tank fixed on a stand.

One of the keys to a residential home’s entire heating system operating dependably, smoothly, and safely is the proper selection and installation of an expansion tank. These days, diaphragm-diaphragm closed type expansion tanks are more frequently installed because they offer both a high degree of operational convenience and an economical price.

Optimal thermal insulation for heating pipes

Self-insulation of heating pipes on the street

Polyethylene pipes for heating private property

In understanding how a closed expansion tank works for heating and insulation in a house, it"s like having a safety valve for your heating system. Picture this: when water heats up in your boiler, it expands. Without a way to accommodate this expansion, pressure can build up and cause damage. That"s where the closed expansion tank comes in. It"s a small tank connected to your heating system, usually near the boiler. When the water expands, instead of building up pressure, it flows into this tank, which has air trapped inside. As the water fills the tank, the air compresses, acting like a cushion, preventing pressure spikes. When the water cools down, the compressed air pushes it back into the system. It"s like a silent partner, ensuring your heating system runs smoothly and safely, without any unexpected hiccups.

Expansion tank for heating closed type installation

When planning the creation of a water heating system in your own home, the owner is faced with a choice of several options. In the list of the most important questions – the type of system (will it be open or closed type), and what will be the principle of transmission of the coolant through the pipes (natural circulation due to the action of gravitational forces, or forced, requiring the installation of a special pump). Expansion tank for heating closed type installation Each of the schemes has its advantages and disadvantages. But still nowadays the closed system with forced circulation is more and more often favored. This scheme is more compact, easier and faster to install, has a number of other operational advantages. One of the main distinguishing features is a fully sealed expansion tank for heating closed type installation of which will be considered in this publication. But before you buy an expansion tank and proceed to its installation, it is necessary to familiarize yourself at least a little with its device, the principle of operation, as well as with what model will be optimal for a particular heating system.

What are the advantages of a closed heating system

Despite the fact that recently there have been a lot of modern devices and systems for heating the premises, the principle of heat transfer through the circulating through the pipes of the liquid with high heat capacity – without a doubt, remains the most common. Water is most often used as a carrier of heat energy, although in some circumstances other liquids with low freezing point (antifreeze) have to be used as well. Water heating is the leader in terms of prevalence The coolant receives heating from the boiler (furnace with a water circuit) and transfers heat to heating devices (radiators, convectors, circuits of "warm floor") installed in the rooms in the required quantity. How to decide on the type and number of heating radiators? Even the most powerful boiler will not be able to create a comfortable atmosphere in the premises if the parameters of heat exchange points do not correspond to the conditions of a particular room. How to properly calculate the required number of radiators – in a special publication of our portal. But any liquid has common physical properties. Firstly, at heating it considerably increases in volume. And secondly, unlike gases – it is an incompressible substance, its thermal expansion must be compensated in some way, providing for this free volume. And at the same time it is necessary to provide that as it cools down and reduces in volume, air does not get into the pipe loops, which will create a "plug", preventing the normal circulation of the coolant. This is exactly the function of the expansion vessel. Not so long ago in private construction, there was no special alternative and did not exist – at the highest point of the system was installed open expansion tank, which quite coped with the tasks at hand. Basic scheme of the open type system 1 – heating boiler; 2 – supply riser; 3 – open expansion tank; 4 – heating radiator; 5 – optional – circulation pump. In this case, a pump unit with a bypass loop and gate valve system is shown. If desired or necessary, forced circulation can be switched to natural circulation and vice versa. Closed system is completely isolated from the atmosphere. It maintains a certain pressure, and the thermal expansion of the liquid is compensated by the installation of a sealed cistern of special design. Differences of the heating system of the closed type The tank on the scheme is shown pos. 6, cut into the return pipe (pos.7). It would seem – why "why make a garden"?? A conventional open expansion tank, if it can fully fulfill its function, seems to be a simpler and less expensive solution. It"s a sure thing. cost a little, and in addition. With certain skills, it is easy to make it yourself – to weld it from steel sheets, to use unnecessary metal containers. for example, an old canister, etc.п. Moreover, you can find examples of using old plastic canisters. Open expansion tank Is there any point in spending money on a sealed expansion tank?? It turns out that there is, since the closed heating system has many advantages:

• Full tightness absolutely excludes the process of evaporation of the coolant. It opens up the possibility of using, in addition to water, special antifreezes. A measure – more than necessary, if the country house in the winter is not used constantly, but "visits", from time to time .
• In an open heating system, the expansion tank, as already mentioned, should be installed at the highest point of the heating system. Very often this is an unheated attic. And that entails the added hassle of insulating the tank. so that even in the most severe frosts the coolant does not freeze in it .

One possible location for an expansion tank is a discrete corner.

Additionally, the expansion tank in a closed system can be placed almost anywhere on the system. The return pipe immediately before the boiler inlet is the best location for installation because the tank components will be less exposed to the heated coolant’s temperature effect there. However, this is by no means indisputable, and it can be mounted using this kind of computation. in order to prevent obstructions with the room’s interior, should the system incorporate a wall-mounted boiler, for instance. placed in the kitchen or hallway.

• In an open expansion tank, the coolant is always in contact with the atmosphere. This leads to constant saturation of the liquid with dissolved air, which is the cause of corrosion activation in the circuit pipes and radiators, to increased gas formation in the heating process. Aluminum radiators are particularly intolerant to this.
• Closed heating system with forced circulation – less inert – it warms up much faster at start-up, much more sensitive to adjustments. Completely unjustified losses in the area of an open-type expansion tank are excluded.
• The temperature difference in the supply and return pipes in the currents of connection with the boiler is less than in the open system. This is important for the safety and longevity of the heating equipment.
• A closed scheme with forced circulation requires smaller diameter pipes to create circuits – there is a gain in material costs and simplification of installation work.
• The expansion tank of the open type must be monitored – to prevent overflow when filling, and to exclude the fall of the liquid level in it in the course of operation below the critical mark. Of course, all this can be solved by installing additional devices, such as float valves, overflow connections, etc., tapped into the pipe, which is installed on the return line.п. but it is an unnecessary complication. In a closed heating system, such problems do not arise.
• Finally, this system is the most universal, as it fits any type of batteries, allows you to connect the circuits of floor heating, convectors, heat curtains. In addition, if desired, it is possible to organize and hot heat supply by mounting an indirect heating boiler in the system.

There is just one significant drawback that can be highlighted. This is the required "safety group," which consists of an automatic air vent, a safety valve, and control and measuring devices (thermometer, pressure gauge). That being said, this is not really a drawback. but a cost of technology guaranteeing the heating system operates safely.

In summary, the benefits of a closed system are immense, and the investment in a specialized hermetic expansion tank appears to be well worth it.

How is organized and how does the expansion tank for heating closed type?

For a closed type system, the expansion tank device is not very complicated:

Schematic diagram showing how a sealed expansion tank works

The entire construction is typically housed in a cylindrical pressed steel case (pos.1) (cisterns in the shape of "tablets" are also available). When producing high-quality metal, an anti-corrosion coating is applied. The cistern’s exterior has an enamel coating. Red-bodied products are meant to be heated. (Blue-colored cisterns are present; however, they serve as the water supply system’s accumulators. All of their components must adhere to stricter sanitary and hygienic regulations, and they are not made to withstand higher temperatures.

There is a threaded socket on one side of the cistern (pos 6). 2) for the heating system’s connection. Fittings are occasionally included with the delivery set to make installation easier.

A nipple valve (pos. 3) is located on the other side and is used to create the necessary pressure in the air chamber beforehand.

A membrane (pos. 6) divides the interior of the tank cavity into two chambers. There is an air chamber (pos. 5) and a chamber for the heating medium (pos. 4) on either side of the spigot.

Low diffusion coefficient elastic material is used to make the diaphragm. It is given a unique shape that guarantees "orderly" deformation in response to variations in chamber pressure.

The working principle is straightforward.

• In the initial position, when connecting the cistern to the system and filling it with coolant, a certain volume of liquid enters the water chamber through the spigot. The pressure in the chambers is equalized and this closed system becomes static.
• As the temperature rises, the volume of coolant in the heating system expands, accompanied by an increase in pressure. The excess fluid enters the expansion tank (red arrow) and bends the diaphragm (yellow arrow) with its pressure. The volume of the coolant chamber increases, while the volume of the air chamber decreases, and the air pressure in it increases.
• When the temperature drops and the total volume of the coolant decreases, the excess pressure in the air chamber helps the diaphragm to move backwards (green arrow) and the coolant moves back into the pipes of the heating system (blue arrow).

The valve in the "safety group" should open to release extra fluid if the heating system’s pressure reaches a certain point. There are expansion tank models that come with their own safety valve.

Expandable tank mounted on a unique bracket

Tank models can differ in terms of their design elements. As a result, they can be assembled without disassembly or with the option to swap out the membrane (a special flange is included for this purpose). The set might come with clamps or brackets to secure the cistern to the wall, or it might have legs to set it on the ground.

The diaphragm’s actual construction may also vary between them.

Disparities between the diaphragm-type and balloon-type diaphragm-equipped expansion vessels (left and right) in terms of design

An expansion tank with a diaphragm is displayed on the left (it was previously discussed above). These are typically not disassembled models. A balloon-shaped membrane composed of elastic material is frequently utilized (see figure on the right). It’s actually a water chamber in and of itself. The diaphragm stretches and expands in volume as pressure rises. These tanks have a collapsible flange that lets you change the membrane on your own in the event that it fails. Nonetheless, the fundamental idea behind how things work remains the same.

Video: Flexcon FLAMCO Expansion Cisterns Device

How to calculate the required parameters of the expansion tank?

The primary consideration for any expansion tank selection for a given heating system should be its working volume.

Calculation according to the formulas

Installing a tank with a capacity equal to roughly 10% of the total coolant flowing through the system’s circuits can still satisfy recommendations. Nonetheless, a more precise computation can be performed using a unique formula designed for this purpose:

In the formula, symbols stand for:

Vb is the expansion vessel’s needed working volume;

Vc is the heating system’s total coolant volume;

K is the coefficient that accounts for the coolant’s volumetric expansion during heating;

D is the efficiency factor of the expansion tank.

Where should one obtain the starting values? Let’s examine each row individually:

1. The total volume of the system ( Vс ) can be determined in several ways:

• It is possible to calculate with a water meter what the total volume will fit when the system is filled with water.
• The most accurate way, which is used when calculating the heating system – is the summation of the total volume of the pipes of all circuits, the capacity of the heat exchanger of the existing boiler (it is specified in the passport data), and the volume of all heat exchange devices in the premises – radiators, convectors, etc.п .
• The simplest method gives quite acceptable error. It is based on the fact that to provide 1 kW of heating power requires 15 liters of coolant. Thus, the boiler nameplate output is simply multiplied by 15.

2. The coefficient of thermal expansion, or k, has a numerical value. It fluctuates nonlinearly in response to the liquid’s heating temperature and the proportion of additives such as ethylene glycol used in antifreeze. The values are displayed in the following table. The heating system’s intended operating temperature is where the heating value line is derived. The percentage of ethylene glycol in water is assumed to be 0. Regarding antifreeze, based on a particular concentration.

Coolant heating temperature, °Ρ

Glycol percentage of the overall volume

3. An additional formula must be used to determine the expansion tank’s efficiency coefficient (D) value.

The heating system’s maximum permitted pressure is denoted by Qm. It will be decided by the safety valve’s threshold of operation in the "safety group," which must be specified in the product passport.

Qα is the air chamber’s pre-pumping pressure in the expansion tank. Additionally, this is mentioned in the product documentation and on the packaging. It can be changed by either filling it with a car pump or, conversely, emptying it through a nipple. It is usually advised to set this pressure between 1.0 and 1.5 atmospheres.

Calculator for calculating the required volume of the expansion vessel

To make the reader’s computation process easier. These dependencies are included in a special calculator in the article. After entering the requested data and clicking "Calculate," you will receive the expansion vessel’s necessary volume.

The selected model is the one with the closest indicators based on the obtained value, which is the minimum value. Only upward rounds are made; the extra volume is not required.

Finally, you will be able to select the best option from the model range of the calculated volume that is offered for sale. according to where the expansion tank is anticipated to be installed—on the floor or fixed to the wall.

There’s still one more detail. Certain heating boilers come with an integrated expansion tank. This does not negate the need for computations, as there are instances where the built-in tank’s volume is obviously insufficient. In this scenario, an additional unit with a working volume equal to the discrepancy between the parameters in the constructed tank and the calculated values for the entire system will need to be purchased and installed.

And one last thing. Installing an expansion tank with a minimum 15-liter capacity is recommended even for small coolant volumes if the heating system works on the forced circulation principle.

Expansion tank for heating closed type installation with your own hands

Installing the expansion tank on one’s own is not difficult for someone with plumbing experience. The diagram illustrates how it taps into the system in principle:

Suggested plan for a closed heating system’s expansion tank tapping

A cut is made on the return pipe (pos. 1), in the vicinity of the heating boiler entrance (pos. 2), preferably in front of the circulation pump (pos. 3). This cut is where a tee is packed (pos. 4). Installation techniques can vary depending on whether metal, polypropylene, or thermoplastic pipes are being used.

The ball valve is packed (pos. 7) on the socket (pos. 6) of the expansion tank itself (pos. 5). Assuring that the expansion tank can be disconnected in the event of repairs or routine maintenance is essential. It makes sense to connect the tap and cistern with a union nut (also known as "American") for the same reason (pos. 8). When the tap is in the working position, it should always be open.

There is a pipe segment that connects the tap to the tee (pos. 9). Its length and configuration (the number of bends or turns) are irrelevant; however, it is typically constructed in the quickest and most practical route possible from the tank installation location to the return pipe.

Let’s now examine the cistern itself and what needs to be done.

An overview of the procedure that needs to be carried out

Expansion tank for heating closed type: device and principle of operation

The heating system is made up of numerous components, each serving a distinct functional purpose, making it a complex engineering construction. One of the most crucial components of the heating system circuit is the expansion tank.

Why is an expansion tank in the heating system necessary??

Because of the temperature increase in the heat-carrying fluid’s volume, heating the coolant in the boiler and heating system circuit greatly increases pressure. This physical phenomenon has the potential to destroy the boiler or pipelines because the liquid is essentially an incompressible medium and the heating system is hermetically sealed. If there were one significant exception, the issue could be resolved by installing a straightforward valve that can release the excess hot coolant volume into the outside atmosphere.

Air will replace the released coolant in the heating circuit when the fluid compresses during cooling. Any heating system’s worst enemy are air plugs, which make network circulation impossible. As a result, the heating radiators must be bled of air. It is very expensive to constantly add new coolant to the system, and heating cold water is more expensive than heating the heat-carrying liquid that the return pipeline brought to the boiler.

Installing a "expansion tank," which is a reservoir connected to the system via a single pipe, solves this issue. The heating expansion tank’s volume balances out the excess pressure inside, enabling steady circuit operation. The form and dimensions of the heating system’s external expansion tanks vary according to the type of heating circuit and the outcomes of computations. These days, tanks come in a variety of shapes, from traditional cylindrical tanks to what are referred to as "tablets."

Types of heating systems

Building heating networks come in two varieties: open and closed. In centralized heating networks, open (gravity) heating systems are utilized to enable direct water intake for hot water supply requirements, something that is not feasible in individual homes. This kind of device is found at the circuit’s highest point in the heating system. Because it can communicate with the outside atmosphere, the heating expansion tank not only levels pressure drops but also serves as a natural air separator for the system.

From a structural standpoint, this apparatus functions as a heating system’s non-pressurized expansion tank. It is fundamentally incorrect to refer to a system with gravity (natural) circulation of the heat-carrying fluid as open.

Use a closed expansion tank heating system with an integrated internal diaphragm in a more contemporary closed scheme.

It is also accurate to refer to such a device as a vacuum expansion tank for heating at times. With this kind of system, the coolant is forced to circulate, and air from the circuit is evacuated via unique taps (valves) that are mounted atop the system pipelines and on the heating devices.

Device and principle of operation

The heating system’s structurally closed expansion tank is a cylindrical vessel with a rubber membrane installed inside that separates the vessel’s internal volume into liquid and air chambers.

There are several types of diaphragms:

• cylinder type, whereby the coolant is inside the rubber cylinder and pressurized air or nitrogen is outside;
• in the form of a diaphragm dividing the internal volume of the expansion tank for a closed heating system into two parts – with water and injected air or gas.

The instructions that are attached to devices like closed-type heating expansion tanks specify how each system’s gas pressure should be adjusted. Certain manufacturers include a membrane replacement option in the design of their expansion tanks. This method slightly raises the device’s initial cost, but in the event that the membrane is harmed or destroyed later on, replacing it will be less expensive than buying a new expansion tank.

Practically speaking, the diaphragm’s shape has no bearing on the devices’ efficiency; the closed-type cylinder expansion tank for heating does, however, have a marginally larger capacity for heat-carrying fluid.

Their working principle is also the same: the diaphragm stretches, compressing the gas on the other side and allowing extra coolant to enter the tank as the water pressure in the network rises as a result of expansion during heating. The process is reversed when the network cools down and, as a result, the pressure decreases. In this manner, the network’s continuous pressure is automatically regulated.

It should be underlined that acquiring the stability of the heating network will be exceedingly challenging if you randomly purchase an expansion tank for the heating system without doing the required computations. The system won’t produce the pressure it needs if the tank is much bigger than it needs to be. An emergency situation could arise if the tank is smaller than necessary because it won’t be able to hold the large amount of liquid that is carrying heat.

Calculation of expansion tanks

The total volume of the system, which includes the volume of the circuit’s pipelines, the heating boiler, and the heating appliances, must be determined before calculating the expansion tank for closed-type heating. The passports of the boiler and heating radiators show their respective volumes, and the area of the pipes’ internal cross-section times their length yields the volume of the pipelines. If the system contains pipelines with varying diameters, each pipeline’s volume must be calculated independently before being added together.

Moreover, the calculation is done using the formula V = (Vs x k) / D for devices like closed-type expansion tanks for heating, where:

Whatever the situation, it should be remembered that expansion tanks for heating should allow for a 10% increase in the network’s coolant volume, or 500 liters of heat-carrying fluid. The total capacity, including the tank, should be 550 liters. As a result, an expansion tank for the heating system that holds at least 50 liters is needed. This method of estimating the volume is highly imprecise and could lead to extra expenses for buying a bigger expansion tank.

Online expansion tank calculators can now be found on the Internet. When choosing equipment with the help of these services, it is essential to perform calculations on three different websites in order to assess how accurate the Internet calculator’s calculation algorithm is.

Maintaining an effective insulation and heating system in your house requires knowing how a closed expansion tank works. This tank is essential to controlling the pressure changes that arise from the system’s water heating up and expanding.

The closed expansion tank aids in preventing excessive pressure buildup, which might otherwise result in damage to pipes, valves, and other heating system components by giving the expanded water a specific area to move into. In closed-loop heating systems, where water circulates constantly, this function is especially crucial.

A closed expansion tank works on a fairly basic but efficient principle. The pressure inside the heating system rises as the water expands as it gets hotter. This expanded water is able to enter the tank and compress the air within because the closed expansion tank serves as a buffer. By compressing the air, the system’s internal pressure is kept constant, avoiding possible harm.

The significance of correctly sizing and installing the closed expansion tank is one important thing to keep in mind. It needs to be big enough to hold the expansion of water without letting the pressure go over safe bounds. For best results, the installation must also be done correctly, including positioning and connecting to the heating system.

To sum up, a closed expansion tank is an essential part of an insulation and heating system that contributes to its safe and effective functioning. Homeowners can effectively manage pressure fluctuations and extend the lifespan of their heating systems by being aware of the principle of operation and making sure that proper sizing and installation are followed.