In a heating system, a very important element is the heating expansion tank. Such a device serves to accept excess coolant at the moment when it expands, thus preventing rupture of the pipeline and taps.
The principle of operation of an expansion tank for heating is as follows: when the temperature of the coolant rises by 10 degrees, its volume increases by about 0.3%. Since the liquid is not burned, excess pressure appears that needs to be compensated. This is precisely why an expansion tank is installed.
Types of expansion tanks
Different types of expansion tanks are used in different heating systems. Previously, systems without circulation pumps used an open expansion tank for heating. But such tanks had many disadvantages, so nowadays they are used very rarely. Due to the fact that air gets into such an expansion tank for heating, corrosion appears, and the liquid evaporates faster and must be constantly replenished. Such a tank must be placed at the highest point of the heating system, and this is not always easy to implement.
Open expansion tank for heating
In such heating systems, where the coolant circulates using a pump, a closed expansion tank for heating is installed; the calculation here is that it is a sealed container that has an elastic membrane inside. A membrane (balloon or diaphragm) divides the tank into two parts. Air or inert gas under pressure is pumped into one part, and the other part is intended for excess coolant. The membrane inside the tank is elastic, so when the coolant enters there, the volume of the air chamber becomes smaller, the pressure in it increases, thus compensating for the high pressure in the heating system. When cooling, the reverse process occurs.
Construction of closed expansion tanks
A closed expansion tank for heating, a flat tank can be flanged (have a replaceable membrane) or with a non-replaceable membrane. The second type is in quite high demand due to its relatively low cost. But flanged expansion tanks are better in many ways - the pressure here can be higher, and if the membrane ruptures, it can be replaced.
The flanged expansion tank of the heating system can be either vertical or horizontal.
Here, the liquid, when it enters the tank, has no contact with the metal surface, since it is located inside the membrane. If the membrane is damaged, it can be replaced through the flange.
Vertical and horizontal flanged tanks
Tanks that do not have a replaceable membrane are fixed rigidly around the entire perimeter. From the very beginning, the diaphragm is pressed against the inner surface, since the volume of the expansion tank for heating is completely filled with gas. After this, the pressure in the heating expansion tank increases, and the liquid goes inside. When the system starts up, the pressure can rise sharply, so this is when the membrane can be damaged.
Selection of expansion tank
Choosing an expansion tank for heating is a responsible matter. In this case, you should definitely pay attention not only to its type and size, but also to the membrane - the following indicators are important: resistance to the diffusion process, operating temperature range, durability, compliance with sanitary requirements.
Today there is a wide range of expansion tanks for heating systems on the market.
In addition, it is necessary to determine the ratio of the boundaries of the pressure range, which is extremely permissible. Before purchasing a tank, be sure to check whether it meets existing quality and safety standards.
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.
Installation of expansion tank
Installation of the expansion tank of the heating system is done in accordance with the project and instructions. Your best option would be to have a specialist do this. If this is not possible, then at least consult with him. The installation of an expansion tank for heating, if it is an open type, is carried out at the highest point of the heating system. A closed tank can be placed almost anywhere, but not directly after the pump.
One of the options for installing an expansion tank in the heating system
It is necessary to pay special attention to such an issue as fastening the heating expansion tank, since the mass of the tank, which is filled with water, increases significantly. Another important point is the possibility and convenience of servicing the tank and free access to it.
Expansion tank maintenance
The role of such a device as the expansion tank of the heating system cannot be underestimated; the instructions for this device provide a list of rules for its maintenance. These include:
- Once every six months it is necessary to check the tank for external damage - corrosion, dents, leaks. If suddenly such damage is found, then it is imperative to eliminate its cause.
- Once every six months, you need to check the initial pressure of the gas space for compliance with the calculated indicator.
- The integrity of the membrane is checked once every six months. If a violation is detected, it must be replaced (if such a possibility is provided).
- If the tank will not be used for a long time, then you need to keep it in a dry place and drain the water from it.
Next is how to check the heating expansion tank - its initial pressure of the gas space. To do this, disconnect the tank from the heating system, drain water from it, and connect a pressure gauge to the nipple of the gas cavity. If the pressure is lower than what was set at the same time when the expansion tank for heating was set up, the tank must be inflated with a compressor through the same nipple.
Pressure gauge readings for correct operation of the expansion tank
Checking the integrity of the membrane is also an important point. If suddenly, while checking the pressure of the gas space after you have drained the water, air flows through the drain valve, and the pressure in the gas space has decreased to atmospheric pressure, then the membrane is broken.
To replace the membrane, you need to go through several steps. First of all, the tank is disconnected from the heating system, then it needs to be drained. Next, the pressure of the gas cavity is released through the nipple. The membrane flange is dismantled. It is located in the area of the pipe connection to the pipes. The membrane included in the expansion tank device for heating is removed from the hole at the bottom of the housing.
Then you need to check the inside of the case to make sure there is no dirt or corrosion; if there is any, you need to remove them and rinse them with water, and then dry them. To remove corrosion, do not use products containing oils! The membrane holder is inserted into the hole at the top of the membrane. The bolt is screwed into the membrane holder, it is placed in the housing, and the holder is retracted into the hole in the bottom of the housing. The holder is then secured with a nut. After this, a membrane flange is placed on the body.
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 tap 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%,
Where, V s— full volume of the heating system; n%— coefficient of expansion of the liquid in the heating system.
Expansion coefficient value n%, 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 .
Where: 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.
The heating system, being a complex engineering structure, consists of many elements that have different functional purposes. The expansion tank for heating is one of the most important parts of the heating system circuit.
When the coolant is heated, the pressure in the boiler and the heating system circuit increases significantly due to the temperature increase in the volume of the coolant fluid. Considering that the liquid is a practically incompressible medium and the heating system is sealed, this physical phenomenon can lead to the destruction of the boiler or pipelines. The problem could be solved by installing a simple valve that could release the excess volume of hot coolant into the external environment, if not for one important factor.
When cooling, the liquid contracts and air enters the heating circuit in place of the discharged coolant. Air jams are a headache for any heating system; they make circulation in the network impossible. Therefore it is necessary. Constantly adding new coolant to the system is very expensive; heating cold water is much more expensive than heating the coolant that came into the boiler through the return pipeline.
This problem is solved by installing a so-called expansion tank, which is a reservoir connected to the system by one pipe. Excess pressure in the heating expansion tank is compensated by its volume and allows for stable operation of the circuit. Externally, expansion tanks for the heating system, based on the calculation results and the type of heating circuit, are different in shape and size. Currently, tanks are produced in various shapes, from classic cylindrical tanks to so-called “tablets”.
Types of heating systems
There are two schemes for building heating networks -. An open (gravity) heating system is used in centralized heating networks and allows water to be directly withdrawn for hot water supply needs, which is impossible in private housing construction. Such a device is located at the top point of the heating system circuit. In addition to leveling pressure drops, the heating expansion tank performs the function of natural separation of air from the system, since it has the ability to communicate with the outside atmosphere.
Thus, structurally, such a device is a compensation tank of the heating system, not under pressure. Sometimes a system with gravitational (natural) circulation of a heat-carrying fluid may be mistakenly called open, which is fundamentally incorrect.
With a more modern closed circuit, an expansion tank of a closed-type heating system with a built-in internal membrane is used.
Sometimes such a device can be called a vacuum expansion tank for heating, which is also true. Such a system provides for forced circulation of the coolant; air is removed from the circuit through special taps (valves) installed on the heating devices and at the top of the system pipelines.
Device and principle of operation
A structurally closed expansion tank in a heating system is a cylindrical tank with a rubber membrane installed inside, which divides the internal volume of the vessel into air and liquid chambers.
Membranes are of the following types:
Gas pressure is adjusted individually for each system, which is described in the instructions supplied with devices such as an expansion tank for closed-type heating. Some manufacturers provide the possibility of replacing the membrane in the design of their expansion tanks. This approach slightly increases the initial cost of the device, but subsequently, if the membrane is destroyed or damaged, the cost of replacing it will be lower than the price of a new expansion tank.
From a practical point of view, the shape of the membrane does not in any way affect the operating efficiency of the devices; it should only be noted that a closed-type balloon expansion tank for heating holds a slightly larger volume of heat-carrying liquid.
The principle of their operation is also the same - when the water pressure in the network increases due to expansion when heated, the membrane stretches, compressing the gas on the other side and allows excess coolant to enter the tank. When it cools down and, accordingly, the pressure in the network drops, the process occurs in the reverse order. Thus, regulation of constant pressure in the network occurs automatically.
It is necessary to focus on the fact that if you buy an expansion tank for the heating system at random, without the necessary calculations, then it will be very difficult to achieve stable operation of the heating network. If the tank size is significantly larger than necessary, the pressure required for the system will not be created. If the tank is smaller than the required size, it will not be able to accommodate the excess volume of heat-carrying liquid, which may result in an emergency situation.
Calculation of expansion tanks
To calculate an expansion tank for closed-type heating, you first need to calculate the total volume of the system, consisting of the volumes of the circuit pipelines, heating boiler and heating appliances. The volumes of the boiler and heating radiators are indicated in their passports, and the volume of pipelines is determined by multiplying the internal cross-sectional area of the pipes by their length. If the system contains pipelines of different diameters, then their volumes should be determined separately and then added together.
Further calculations for devices such as an expansion tank for closed-type heating are carried out using the formula V = (Vc x k) / D, where:
Vс – volume of heat-carrying fluid in the heating system,
k – coefficient volumetric thermal expansion, taken for water 4%, for 10% ethylene glycol - 4.4%, for 20% ethylene glycol - 4.8%;
D is an indicator of the efficiency of the membrane unit. It is usually indicated by the manufacturer or can be determined by the formula: D = (Рм – Рн) / (Рм +1), where: 
Рм – the maximum possible pressure in the heating network, usually it is equal to the maximum operating pressure of the safety valve (for private houses it rarely exceeds 2.5 - 3 atm.)
Рн – initial pumping pressure of the air chamber of the expansion tank, taken as 0.5 atm. for every 5 meters of height of the heating system circuit.
In any case, it should be assumed that expansion tanks for heating should provide an increase in the volume of coolant in the network within 10%, that is, if the volume of coolant in the system is 500 liters, the volume together with the tank should be 550 liters. Accordingly, an expansion tank of the heating system with a volume of at least 50 liters is required. This method of determining volume is very approximate and can result in unnecessary costs for purchasing a larger expansion tank.
Currently, online calculators for calculating expansion tanks have appeared on the Internet. If such services are used to select equipment, it is necessary to carry out calculations on at least three sites to determine how correct the calculation algorithm of a particular Internet calculator is.
Manufacturers and prices
Currently, the problem of buying an expansion tank for heating lies only in the correct selection of the type and volume of the device, as well as the financial capabilities of the buyer. The market offers a wide selection of instrument models from both domestic and foreign manufacturers. However, it should be noted that if the purchase price for such devices as a closed-type expansion tank for heating is much lower than that of its main competitors, then it is better to refuse such a purchase.
The low cost indicates the unreliability of the manufacturer and the low quality of the materials used in its manufacture. Often these are products from China. As with all other goods, the price for a high-quality expansion tank for heating will not have a significant difference of about two to three times. Conscientious manufacturers use approximately the same materials, and the difference in price of models with similar parameters of about 10-15% is determined only by the location of production and the pricing policy of sellers.
Domestic manufacturers have proven themselves well in this market segment. By installing modern technological lines in their production, they achieved the production of products whose parameters are not inferior to the best global brands at a lower cost.
It should be borne in mind that it is important not only to buy an expansion tank for closed-type heating, it also requires its correct installation.
Having the necessary skills and following the instructions, you can install it yourself. If the technician still has any doubts about his knowledge, then it is best to turn to professionals to guarantee stable operation of the heating network and eliminate possible malfunctions.
A correctly selected and correctly installed expansion tank of the heating system will prevent its failure and will maintain the pressure at the required level. It is needed as a reserve for water expanding when heated. Depending on the type of system, the built-in expander can be open or closed.
We will tell you how to select a reserve capacity depending on the heating scheme being created. The article we presented describes the design features and specifics of installing expanders. Recommendations are given that, if followed, will ensure ideal operation of any type of heating circuit.
A design feature of open type expanders is the contact of the coolant with the atmosphere. The circulation in systems with an expander of this type is convection. When heated, the volume of liquid increases, its excess is absorbed by the reservoir of the container.
When the temperature drops, the liquid returns by gravity, under the influence of gravity.
Due to zero pressure in the tank, the device does not require a strong metal structure, therefore:
- any metal is used in the manufacture of the case;
- a ready-made container made of heat-resistant plastic can be used;
- The shape of the tank is not important.
In country houses, such equipment can be assembled from available materials. As a container, you can use a plastic canister or barrel equipped with an inlet pipe and an outlet for overflow.
Open type expanders can be made in the form of a rectangular tank with a leak-proof lid on the top plane
Externally, it is an ordinary metal tank, the upper plane of which is equipped with a hole for servicing and adding liquid. The leak-proof lid provides protection against clogging. Fastening units are provided at the bottom or on the side plane.
Image gallery
The expander itself can be installed at any point in the system, but when performing installation work it is advisable to take into account the following recommendations:
- the best place for installation is the return line, to the pump insertion point;
- It is better to supply coolant from above, which will reduce air penetration and maintain functionality if the membrane is damaged;
- the lack of main volume can be compensated by installing an additional expander with a smaller capacity.
When installing, it is not forbidden to take into account the interior of the room, if necessary. To control the level, the expander must be equipped with a pressure gauge.
A closed expander is usually placed in front of the boiler, before the circulation pump is installed
The possibility of placement close to the boiler eliminates the question of the need to insulate the tank. The equipment is located in a warm room, which ensures ease of use.
Which design is better?
Systems, depending on the design and material of the expansion tank, differ in the list of pros and cons. But, according to experts and experienced users, the advantages in functionality are on the side of closed options.
Pros and cons of an open tank
A self-flowing system requires larger diameter pipes, which in turn directly increases costs. The budget for installations with a leaky expander increases slightly, although it remains relatively small.
The main advantages of this option are simplicity, plus the low cost of components and installation work. Another positive feature is that there is no need to control the pressure level.
An open-type expander for small systems can be assembled from available materials, and its installation will not be difficult
However, there are much more disadvantages:
- the use of anti-freeze is dangerous due to toxic fumes;
- installation possibilities are limited only by the top point of the system;
- constant contact with the atmosphere increases the risk of air locks and corrosion;
- slow warm-up;
- temperature changes accompanying convection circulation accelerate equipment wear;
- used in heating low-rise buildings, maximum two floors;
- large heat losses and energy consumption for heating.
Another disadvantage of an open system is losses from evaporation and overflows. Therefore, when installing the tank, care should be taken to ensure that the filler hole is accessible.
Image gallery
What is the purpose of installing an expansion tank? The heating system is filled with a fixed amount of liquid (water or antifreeze), which is prone to thermal expansion. This means that an increase in coolant temperature inevitably leads to an increase in pressure in the system. Since pipes, radiators and other elements of the engineering structure are inelastic, increased pressure will lead to depressurization of the system - a breakthrough will occur at the weakest point.
Water has low compressibility, so a special device is built into the system - a membrane or open tank. Its function is that as pressure increases, air will be compressed. This makes it possible to provide protection against water hammer. The installed expansion tank protects the system from excessive pressure build-up.
The main task is to perform reliable installation of the tank
Membrane tanks are designed for a closed-type heating system - they are a container with an elastic, waterproof membrane inside, which divides the internal volume into two parts. The membrane is needed to prevent air from coming into contact with the coolant. Otherwise, airing of the network and an increased risk of corrosion of steel elements of the system cannot be avoided.
In an open-type system, the tank communicates with the atmosphere, due to which air is released from the pipes. For this reason, the installation location of an open tank is strictly regulated - it must be located at the highest point of the system.
How to connect an expansion tank
How to reliably connect an expansion tank in an open system!? An open-type heating system is characterized by the fact that the movement of coolant in it is ensured by convection.
The operating principle is as follows: the coolant heated by the boiler unit is delivered directly to the highest point of the system, as a result of which it flows by gravity into the heating radiators and, when cooled, returns to the boiler through the return pipeline. There is always dissolved oxygen in water, which is released through the process of convection, which means that air bubbles tend to rise.
When considering this diagram, it becomes obvious that the only possible installation location for the expansion tank is the top point of the system. For a single-pipe system, this is the upper part of the accelerating manifold.
Connection diagram for a membrane tank in an open type heating system As a tank, you can use any container of a suitable size made of heat-resistant material. A lid (not sealed) is needed only to protect it from debris getting into the system. If you don’t have a small metal barrel at hand, the tank is welded from sheet steel 3-4 mm thick.
The tank must be installed in compliance with certain rules, in particular:
- the tank must be placed above the boiler unit and connected by a vertical riser through which heated water is supplied;
- It is recommended to insulate the body of the tank to reduce heat loss, especially if the tank is located in an uninsulated attic of the house.
Over time, the water from the tank evaporates and needs to be topped up periodically. This can be done using an ordinary bucket. If the tank is installed in the attic, where it is difficult to reach, a water supply pipe is led to the installation site of the tank, and an emergency overflow is organized to avoid flooding the house with hot water in the event of an emergency. The emergency overflow pipe is usually connected to the sewer network, but owners of private houses often simplify the task by leading it outside through a wall or roof.
Expansion tank in a closed heating system
Equipment for the heating system is selected at the design stage, taking into account the requirements for the performance of the boiler unit, the length of pipelines and the volume of coolant involved. A diagram is being developed that indicates the installation locations of all system elements, including the expansion tank. In a closed heating system, it is necessary to use a membrane device.
Expander in a closed heating system When linking a project to an existing boiler room, it is important to take into account the following points:
- The tank should be placed in such a way as to ensure normal access for installation and further maintenance. Floor-standing models are not recommended to be installed close to the wall.
- If the device is mounted on a wall, it is advisable to place it at such a level that you can easily reach the air spool and shut-off valve. Typically, the tank is placed under the ceiling of the room only if it is not possible to mount it at a convenient height.
- The supply pipe should not be placed on the floor across the passage or suspended at human height.
- The pipes connected to the expansion tank must be secured to the wall. It is important to avoid a situation where the load from them and from the shut-off valves falls on the tank pipes. Separate mounting of pipes and taps makes it easier to replace the expansion device in case of failure.
At the equipment selection stage, it is necessary to calculate the required volume of the expansion tank. The minimum value of this parameter is 1/10 of the total volume of liquid circulating in the system. It is permissible to use a larger tank. But a tank that is not large enough can become a source of problems, since it is not able to compensate for the increased pressure in the system.
Rules for placing the expansion tank For approximate calculations of the volume of coolant in the system, you can take the thermal power of the boiler unit as a basis. On average, 15 liters of liquid are used per kilowatt. Exact calculations are made taking into account the length of pipelines, volume of radiators, etc.
Important! Many models of gas and electric boilers are mini-boiler rooms, that is, they are immediately equipped with a pump for forced circulation of the coolant, as well as an expansion tank. There is no need to purchase a separate tank if the parameters of the built-in membrane tank are sufficient to ensure the functionality and safety of the existing heating system.
When purchasing a membrane expansion tank, pay attention to whether the selected model has a safety valve, thanks to which excess pressure is automatically released. If one is not provided for by the design of the device, you should buy a safety valve separately and install it in close proximity to the tank.
Where is the best place to put the tank?
The optimal place for installing a membrane tank is a straight section of the pipeline, which is characterized by laminar flow of water, that is, the absence or minimal amount of turbulence. A convenient place is the spill area near the circulation pump.
Note! The expansion tank of a closed heating system can be installed at any convenient height. There is no need to place it at the highest point, since it functions solely as a surge protector. Unlike an open-type heating system, the air accumulated in the pipeline is released using special valves - air taps.
From a hydraulic point of view, it is best to install the membrane tank on the return line so that the circulation pump is located between it and the boiler. In this case, the pumping equipment will function optimally.
Scheme of possible tank placement If desired, the tank can be placed on the supply line; this will not affect the operational properties of the heating system. But the membrane tank itself will not last a relatively long time, since the polymer membrane will be in constant contact with the coolant that has just been heated to 90 degrees, and not with water that has cooled to 45-60 degrees and returned through the pipeline.
Attention! Installing a membrane tank on the supply line is highly not recommended if the heating boiler is solid fuel. There is a risk that due to an emergency, the water in the boiler will begin to boil and steam will enter the tank. Water vapor, like air, is a compressible medium, which is why the membrane will not be able to compensate for the thermal expansion of water.
Expansion tank installation process
Now let's figure out how to install an expansion tank in the heating system. There is an important rule for connecting the device: the tank must be connected to the heating system mains using a shut-off ball valve with an American connection. This installation principle makes it possible, if necessary, to shut off the flow of water in the system at any time, remove the faulty membrane tank and install a new one.
Otherwise, you would have to wait for the coolant to cool down and dismantle part of the piping. Ideally, a tee is installed on the supply line, as well as a second tap - in this case, before removing the expansion tank, it can be emptied into a substitute container.
By hanging the expander upside down, if the diaphragm malfunctions, the unit will fail immediately How to correctly orient a membrane expansion tank in space? The tank is installed with the air chamber up or down, and the container is placed “on its side”. From the point of view of operational characteristics, this does not matter much, since in any case the device will perform its functions properly.
However, it is worth considering this point: if the air compartment is located at the bottom, then the coolant is supplied from above, and the bubbles of air dissolved in it will rise into the pipeline and be removed using an air valve. Otherwise, an air bubble will form in the “water” compartment of the membrane tank over time.
In turn, when the tank is positioned with the air chamber upward, its service life is extended. Over time, from constant contact with hot water, the polymer membrane loses its tightness and cracks appear in it. If the air chamber is located at the bottom, then water will immediately begin to seep into the air compartment, which will quickly damage the expansion tank, while air will penetrate into the coolant. When the air chamber is located on top, the diffusion of water through cracks occurs many times slower, and the device can operate much longer.
Useful tips:
- If you install a pressure gauge next to the expansion tank and the valve, thanks to which the heating system is fed from the water supply, it will allow you to control the pressure in the system in order to bleed off excess in time if the safety valve spool is stuck and does not operate automatically.
- Frequently repeated release of pressure by the valve indicates that the capacity of the expansion tank is selected incorrectly. Instead of changing it to a larger tank, just connect a second tank in parallel.
- Replacing the existing expansion tank with a larger one or connecting a second one will also be required if it is decided to replace the water in the system with antifreeze. This is due to the fact that non-freezing coolants have a higher coefficient of thermal expansion.
If there is no pressure gauge, the circuit of the expansion tank should be equipped with a safety group Settings
Before connecting the tank and filling it with coolant, you need to check the pressure level in the air chamber of the tank - it must correspond to the pressure in the heating system. For this purpose, you should remove or unscrew the plastic plug that covers the spool valve (similar to those installed in car cameras). Using a pressure gauge, it is necessary to measure the pressure and adjust it to the indicators of the heating system. To do this, air is pumped up by a pump or, vice versa, it is bleed by pressing the spool rod.
Note! The tank should be adjusted so that the pressure in its air chamber is 0.2 bar less than the design pressure in the system filled with coolant. If the pear-shaped membrane is not pressed on the water injection side, the coolant, compressing during the cooling process, will be able to draw air through.
After completing the settings, open the tap and fill the entire system with coolant. Then the boiler unit starts up.
The adjustment step is not required if the factory pressure in the air compartment of the expansion tank corresponds to the required parameters. Manufacturers of some brands of equipment indicate the pressure level in the tank on the packaging, which makes it possible to select the optimal option when purchasing.
Conclusion
You can correctly install the expansion tank and prepare the customized membrane tank for operation yourself, without the help of a specialist. The experience gained may be useful in the future if you need to quickly determine the source of problems associated with a decrease or surge in pressure in the system, due to which the burner flame goes out. In such cases, it is recommended that you first carefully inspect the system for coolant leaks and measure the pressure in the air chamber of the membrane reservoir.
