Membrane expansion tank in the heating system. What pressure should be in the expansion tank. Membrane expansion tank of the heating system: the principle of operation, how to choose. Purpose, pros and cons

An expansion membrane tank is a mandatory component, without which the functioning of the system is not possible. It is he who creates the necessary pressure for the full operation of the water supply system, makes reserve water supplies and even performs a number of protective functions. In connection with such a high importance of equipment, the question naturally arises: how to choose and correctly install a tank? To understand, let's approach the issue in a complex way: to your attention the structure and principles of operation of the expansion device, its types, features of choice, as well as the connection diagram and useful instruction video setup.

Functions and working principle

A membrane tank is a sealed, predominantly metal tank, consisting of two separated chambers: air and water. A special rubber membrane acts as a separator - it is usually made of strong butyl, which is resistant to the development of bacterial microorganisms. water chamber equipped with a pipe through which water is supplied directly.

The main task of the expansion membrane tank is to accumulate a certain volume of water and supply it at the request of the user under the required pressure. But the functions of the device are not limited to this - it also:

protects the pump from premature deformation: due to the water reserve, the pump does not turn on every time the tap is opened, but only when the tank is empty;
protects against water pressure drops when several taps are used in parallel;
protects against hydraulic shocks that can potentially occur when the pumping unit is turned on.

Instrument operation

The principle of operation of the tank is as follows. When the pump is turned on, water begins to be pumped into the water chamber under pressure, and the volume of the air chamber at this time decreases. When the pressure reaches the maximum allowable mark, the pump turns off and the water supply stops. Then, as water is taken from the tank, the pressure decreases and, when it decreases to the minimum allowable mark, the pump turns on again and resumes pumping water.

Advice. During the operation of the tank, air can accumulate in the water chamber, which provokes a decrease in the efficiency of the equipment, therefore, at least once every 3 months, it is necessary to carry out maintenance of the compartment - to bleed excess air from it.

Types of membrane tanks

There are two types of expansion membrane tanks:

Advice. When choosing between a replaceable and a permanent diaphragm, consider one important factor: in the first case, the water is completely in the membrane and does not come into contact with the inner surface of the tank, which eliminates corrosion processes, and in the second case, contact is maintained, so it is impossible to achieve maximum protection against corrosion.

Features of choosing a tank

The main factor in choosing a membrane tank is its volume. When calculating the optimal volume of the tank, the following nuances should be taken into account:

the number of users of the water supply system;
number of water intake points: taps, outlets for shower and jacuzzi, outlets for household appliances and boilers that work with water;
pump performance;
the maximum number of pump on/off cycles per hour.

To calculate the approximate volume of the tank, you can use the following guidelines from specialists: if the number of users is no more than three, and the pump capacity is no more than 2 cubic meters / h, then a tank with a volume of 20-24 liters is enough; if the number of users is from four to eight, and the pump performance fluctuates between 3-3.5 cubic meters / h, a tank with a volume of 50-55 liters will be required.

When choosing a tank, remember: the more modest its volume, the more often you have to turn on the pump and the higher the risk of pressure drops in the plumbing system.

Advice. If you assume that over time there will be a need to increase the volume of the membrane tank, buy equipment with the ability to connect additional tanks.

Tank connection diagram

The membrane tank can be installed both vertically and horizontally, but in both cases the connection diagram will be identical:

Determine the mounting location. The device must be located on the suction side of the circulation pump and before the branching of the water supply. Make sure that the tank has free access for maintenance work.
Secure the tank to a wall or floor with rubber grommets and ground it.
Connect a five-pin fitting to the tank nozzle using an American fitting.
Connect in series to the four free outlets: a pressure switch, a pipe from the pump, a pressure gauge and a branch pipe that supplies water directly to the intake points.

Tank connection

It is important that the cross section of the water pipe to be connected is equal to or slightly larger than the cross section of the inlet pipe, but in no case should it be smaller. Another nuance: between the expansion tank and the pump, it is advisable not to have any technical devices so as not to provoke an increase in hydraulic resistance in the water supply system.

Instructions for setting up equipment

After the membrane tank is installed and connected, it is important to correctly configure and start it. Let's dwell on the main points of this stage.

The first step is to find out the internal pressure of the tank. In theory, it should be 1.5 atm, but it is possible that during the storage of the device in a warehouse or during transportation, a leak occurred, which provoked a decrease in such an important indicator. To make sure the pressure is correct, remove the spool cap and measure with a pressure gauge. The latter can be of three types: plastic - cheap, but not always accurate; mechanical automobile - more reliable and relatively affordable; electronic - expensive, but as accurate as possible.

After measurements, you need to decide which pressure will be the most optimal in your case. Practice shows that for the normal functioning of plumbing and household appliances the pressure in the membrane tank should vary within 1.4-2.8 atm. Let's assume that you have chosen these indicators - what to do next? First, if the initial pressure in the tank turned out to be lower than 1.4-1.5 atm, it must be increased by pumping air into the corresponding chamber of the tank. Then you should adjust the pressure switch: open its cover and use the large nut P to set the maximum pressure indicator, and with the small nut ∆P - the minimum indicator.

The setup process is simple

Now you can start the system: as you pump water, watch the pressure gauge - the pressure should gradually rise, and after it reaches the maximum set mark, the pump should turn off.

As you can see, without an expansion membrane tank, you really can not even count on the full-fledged operation of an individual water supply. Therefore, if you want to uninterruptedly enjoy the benefits of civilization, thoroughly approach the choice and connection of the device - all the principles and subtleties are in front of you, so we advise you to study them well and only then proceed to action.

Calculation of the volume of the accumulator: video

Membrane expansion tank for water supply: photo

The heating system, being a complex engineering structure, consists of many elements with 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 heat-carrying liquid. Given that the liquid is a practically incompressible medium, and the heating system is hermetic, this physical phenomenon can lead to the destruction of the boiler or pipelines. The problem could be solved by installing a simple valve that can bleed the excess volume of hot coolant into the external environment, if not for one important factor.

During cooling, the liquid contracts and air enters the place of the discharged coolant into the heating circuit. Air locks- a headache of any heating system, because of them, circulation in the network becomes impossible. Therefore it is necessary. The constant addition of a new coolant to the system is very expensive, heating cold water it is much more expensive than heating the heat-carrying liquid that came to the boiler through the return pipeline.

This problem is solved by installing the so-called expansion tank, which is a tank connected to the system with one pipe. Excessive pressure in the heating expansion tank is compensated by its volume and ensures stable operation of the circuit. Externally, expansion tanks for the heating system, based on the results of the calculation and the type of heating circuit, are different in shape and size. Currently, tanks are produced in various shapes, from classic cylindrical tanks to the so-called "tablets".

Types of heating systems

There are two schemes for the heating networks of the building -. An open (gravity-flowing) heating system is used in centralized heating networks and allows you to directly take water for hot water 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 air separation from the system, as it has the ability to communicate with the outside atmosphere.

Thus, structurally, such a device is a compensation tank of the heating system that is not under pressure. Sometimes, by mistake, a system with gravitational (natural) circulation of a heat-carrying fluid can be called open, which is fundamentally wrong.

With a more modern closed circuit, an expansion tank of the heating system is used closed type with built-in inner membrane.

Sometimes such a device can be called a vacuum expansion tank for heating, which is also true. Such a system provides for the forced circulation of the coolant, while air is removed from the circuit through special taps (valves) installed on the heaters and at the top of the system pipelines.

Device and principle of operation

Structurally, a closed expansion tank in a heating system is a cylindrical tank with a rubber membrane installed inside, which separates the internal volume of the vessel into air and liquid chambers.

The membranes are of the following types:

The gas pressure is adjusted for each system in individually, which describes the instructions attached to such devices as an expansion tank for heating a closed type. Some manufacturers in the design of their expansion tanks provide for the possibility of replacing the membrane. This approach somewhat increases the initial cost of the device, but later, 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 affect the efficiency of the devices, it should only be noted that a slightly larger volume of heat-carrying liquid can fit into a closed-type balloon expansion tank for heating.

Their principle of operation is also the same - with an increase in water pressure in the network due to expansion when heated, the membrane stretches, compressing the gas on the other side and allowing excess coolant to enter the tank. During cooling and, accordingly, a drop in pressure in the network, the process takes place in the reverse order. Thus, the regulation of constant pressure in the network occurs automatically.

It is necessary to focus on the fact that if you buy an expansion tank of the heating system at random, without the necessary calculation, then the stability of work heating network will be very difficult to achieve. If the tank is much larger than necessary, the pressure required for the system will not be created. If the tank is smaller than the required size, then it will not be able to accommodate the excess volume of the heat-carrying liquid, which can result in an emergency.

Calculation of expansion tanks

To calculate an expansion tank for closed-type heating, you first need to calculate the total volume of the system, which consists of the volumes of the pipelines of the circuit, the heating boiler and heating devices. The volumes of the boiler and heating radiators are indicated in their passports, and the volume of pipelines is determined by multiplying the area of \u200b\u200bthe internal cross section pipes for their length. If there are pipelines in the system different diameters, then you should determine their volumes separately, and then add them.

Further, for devices such as an expansion tank for closed-type heating, the calculation is carried out according to the formula V = (Vc x k) / D, where:

Vc is the 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 the efficiency indicator of the membrane unit. Usually it is indicated by the manufacturer or it can be determined by the formula: D \u003d (Rm - Rn) / (Rm +1), where:

Pm - the maximum possible pressure in the heating network, usually it is equal to the maximum working pressure of the safety valve (for private houses it rarely exceeds 2.5 - 3 atm.)
Рн is the pressure of the initial pumping of the air chamber of the expansion tank, taken as 0.5 atm. for every 5 meters of the height of the heating 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, with a volume of heat-carrying fluid in the system of 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 the volume is very approximate and may result in unnecessary costs for the purchase of a larger expansion tank.

Currently, online calculators for calculating expansion tanks have appeared on the Internet. In the case of using such services for the selection of equipment, it is necessary to carry out calculations on at least three sites in order to determine how correct the algorithm for calculating one or another Internet calculator is.

Manufacturers and prices

At present, 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 in the financial capabilities of the buyer. There is a wide choice of models of devices of both domestic and foreign manufacturers on the market. 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 the main competitors, then it is better to refuse such an acquisition.

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 products, for a high-quality expansion tank for heating, the price will not have a significant difference of about two - three times. Conscientious manufacturers use approximately the same materials and the price difference of models similar in 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 have achieved the release of products that are not inferior in their parameters to the best world 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, while following the instructions, it is possible to self-installation. If the master still has any doubts about his knowledge, then it is best to turn to professionals to ensure the stable operation of the heating network and eliminate possible malfunctions.

When planning the creation of a water heating system in own house, the owner is faced with a choice of several options. The list of the most important questions includes the type of system (whether it will be open or closed), and what principle the coolant will be transferred through pipes (natural circulation due to the action of gravitational forces, or forced, requiring the installation of a special pump).

Each of the schemes has its own advantages and disadvantages. But still, nowadays, more and more preference is given to a closed system with forced circulation. Such a scheme is more compact, easier and faster to install, and has a number of other operational advantages. One of the main distinctive features - This is a fully sealed expansion tank for heating of a closed type, the installation of which will be discussed in this publication.

But before you purchase an expansion tank and proceed with its installation, you need to at least get a little familiar with its device, the principle of operation, as well as which model will be optimal for a particular heating system.

IN what are the advantages of a closed heating system

Although Recently, a lot of modern devices and space heating systems have appeared, the principle of heat transfer through a liquid with a high heat capacity circulating through pipes - without a doubt, remains the most widespread. Water is most often used as a carrier of thermal energy, although in some circumstances other liquids with a low freezing point (antifreeze) must be used.

The heat carrier receives heat from the boiler (furnaces with water circuit) and transfers heat to heating devices (radiators, convectors, "warm floor" circuits) installed in the premises in the required quantity.

How to determine 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 the heat exchange points do not correspond to the conditions of a particular room. As it is right - in a special publication of our portal.

But any liquid has common physical properties. First, when heated, it significantly increases in volume. And secondly, unlike gases, this is an incompressible substance, its thermal expansion must be compensated in some way, providing free volume for this. And at the same time, it is necessary to provide that, as it cools and decreases in volume, air does not enter the pipe circuits from the outside, which will create a “plug” that prevents the normal circulation of the coolant.

It is these functions that the expansion tank performs.

Still not so much in private construction, there was no special alternative - at the highest point of the system, an open expansion tank was installed, which completely coped with the tasks.

1 - heating boiler;

2 - supply riser;

3 - an open expansion tank;

4 - heating radiator;

5 - optional - circulation pump. In this case, a pumping unit with a bypass loop and a valve system is shown. If desired, or if necessary, you can switch forced circulation to natural, and vice versa.

You may be interested in information on how to properly carry out

Prices for circulation pumps

circulation pumps

A closed system is completely isolated from the atmosphere. A certain pressure is maintained in it, and the thermal expansion of the liquid is compensated by the installation of a sealed tank of a special design.

The tank in the diagram is shown pos. 6, embedded in the return pipe (pos. 7).

It would seem - why "to fence the garden"? A conventional open expansion tank, if it fully copes with its functions, seems to be a simpler and more inexpensive solution. It probably costs a little, and besides, with certain skills, it is easy to make it yourself - weld it from steel sheets, use unnecessary metal container, for example, old can etc. . Moreover, one can meet examples applications old plastic cans.

Does it make sense to spend money on a sealed expansion tank? It turns out that there is, since a closed heating system has many advantages:

Complete tightness absolutely excludes the process of evaporation of the coolant. This opens up the possibility of using, in addition to water, special antifreezes. The measure is more than necessary if country house V winter time they do not use constantly, but "arrivals", occasionally.
In an open heating system, the expansion tank, as already mentioned, must be mounted at the highest point. Very often, an unheated attic becomes such a place. And this entails additional troubles for the thermal insulation of the container, so that even in the most severe frosts the coolant in it does not freeze.

And in a closed system, an expansion tank can be installed in almost any part of it. The most appropriate place for installation is the return pipe directly in front of the boiler inlet - here the parts of the tank will be less exposed to temperature effects from the heated coolant. But this is by no means a dogma, and it can be mounted in such a way that it does not interfere and does not disharmony with its appearance with the interior of the room, if, say, the system uses a wall-mounted boiler installed in the corridor or in the kitchen.

In an open expansion tank, the coolant is always in contact with the atmosphere. This leads to a constant saturation of the liquid with dissolved air, which is the reason for the activation of corrosion in the pipes of the circuit and in radiators, to increased gas formation during the heating process. Aluminum radiators are especially intolerant of this.
A closed heating system with forced circulation is less inert - it warms up much faster at start-up, much more sensitive to adjustments. Completely unjustified losses in the area of the open expansion tank are excluded.
The temperature difference in the supply pipe and in the return pipe in the currents connected to the boiler is less than in an open system. This is important for the safety and durability of heating equipment.
A closed circuit with forced circulation to create circuits will require tons of smaller diameter pipes - there is a gain both in material costs and in simplifying installation work.
An open-type expansion tank must be controlled to prevent overflow during filling, and to prevent the liquid level in it from falling below a critical level during operation. Of course, all this can be solved by installing additional devices, for example, float valves, overflow pipes, etc., but these are unnecessary complications. In a closed heating system, such problems do not arise.
And, finally, such a system is the most versatile, as it is suitable for any type of batteries, it allows you to connect floor heating circuits, convectors, thermal curtains. In addition, if desired, hot heat supply can also be arranged by installing an indirect heating boiler in the system.

Of the serious shortcomings, only one can be mentioned. This — mandatory "safety group", including instrumentation (pressure gauge, thermometer), safety valve and automatic air vent. However, it is rather no no prosperity, but a technological cost that ensures the safe operation of the heating system.

In a word, the advantages of a closed system clearly outweigh, and spending on a special hermetic expansion tank looks quite justified.

How is the expansion tank for closed-type heating arranged and how does it work?

The expansion tank device for a closed-type system is not very complicated:

Usually the whole structure is placed in a steel stamped case (pos. 1) of a cylindrical shape (there are tanks in the form of a “tablet”). For the manufacture of high-quality metal with an anti-corrosion coating is used. Outside the tank is covered with enamel. For heating, products with a red body are used. (There are tanks of blue color- but these are water accumulators for the water supply system. They are not designed for elevated temperatures, and all their parts are subject to increased sanitary and hygienic requirements).

On one side of the tank there is a threaded pipe (pos. 2) for tapping into the heating system. Sometimes fittings are included in the package to facilitate installation work.

On the opposite side there is a nipple valve (pos. 3), which serves to pre-create the necessary pressure in the air chamber.

Inside, the entire cavity of the tank is divided by a membrane (pos. 6) into two chambers. On the side of the branch pipe there is a chamber for the coolant (pos. 4), on the opposite side - air (pos. 5)

The membrane is made of an elastic material with a low diffusion index. It is given a special shape, which provides an "ordered" deformation when the pressure in the chambers changes.

The principle of operation is simple.

In the initial position, when the tank is connected to the system and filled with coolant, a certain volume of liquid enters the water chamber through the pipe. The pressure in the chambers equalizes, and this closed system takes on a static position.
With an increase in temperature, the volume of the coolant in the heating system expands, accompanied by an increase in pressure. Excess liquid enters the expansion tank (red arrow), and bends the membrane with its pressure (yellow arrow). At the same time, the volume of the chamber for the coolant increases, and the volume of the chamber for the air, respectively, decreases, and the air pressure in it increases.
With a decrease in temperature and a decrease in the total volume of the coolant, the excess pressure in the air chamber contributes to the movement of the membrane back (green arrow), and the coolant moves back into the pipes of the heating system (blue arrow).

If the pressure in the heating system reaches a critical threshold, then the valve in the "safety group" should work, which will release excess fluid. Some models of expansion tanks have their own safety valve.

Different models of tanks may have their own design features. So, they are non-separable or with the possibility of replacing the membrane (a special flange is provided for this). The kit may include brackets or clamps for mounting the tank on the wall, or there may be stands - legs for placing it on the floor.

In addition, they may differ in the design of the membrane itself.

On the left is an expansion tank with a membrane - diaphragm (it has already been discussed above). As a rule, these are non-separable models. Often a balloon-type membrane is used (figure on the right), made of an elastic material. In fact, it is itself a water chamber. With increasing pressure, such a membrane is stretched, increasing in volume. It is these tanks that are equipped with a collapsible flange, which allows you to independently replace the membrane in the event of its failure. But the basic principle work does not change at all.

Video: device expansion tanks brand "Flexcon FLAMCO»

Prices for Flexcon expansion tanks FLAMCO

Flexcon expansion tanks

How to calculate the required parameters of the expansion tank?

When choosing an expansion tank for a particular heating system, its working volume should be a fundamental point.

Calculation by formulas

You can find recommendations to install a tank, the volume of which is approximately 10% of the total volume of coolant circulating through the circuits of the system. However, it is possible to carry out a more accurate calculation - for this there is a special formula:

Vb =Vwith ×k / D

The symbols in the formula are:

Vb- the required working volume of the expansion tank;

Vс- the total volume of the coolant in the heating system;

k- coefficient taking into account the volumetric expansion of the coolant during heating;

D- coefficient of efficiency of the expansion tank.

Where to get the initial values? Let's go in order:

The total volume of the system ( VWith) can be defined in several ways:

It is possible to detect by the water meter what total volume will fit when the system is filled with water.
The most accurate method that is used in calculating the heating system is the summation of the total volume of pipes of all circuits, the capacity of the heat exchanger of the existing boiler (it is indicated in the passport data), and the volume of all heat exchange devices in the premises - radiators, convectors, etc.
Quite acceptable error gives the simplest way. It is based on the fact that 15 liters of coolant are required to provide 1 kW of heating power. Thus, the nominal power of the boiler is simply multiplied by 15.

2. The value of the coefficient of thermal expansion ( k) is a tabular value. It varies non-linearly depending on the heating temperature of the liquid and on the percentage of antifreeze in it. ethylene glycol additives. The values are shown in the table below. The heating value line is taken from the calculation of the planned operating temperature of the heating system. For water, the value of the percentage of ethylene glycol is taken - 0. For antifreeze - based on a specific concentration.

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

3. The value of the efficiency coefficient of the expansion tank ( D) will have to be calculated using a separate formula:

D = (Qm – Qb ) / (Qm + 1 )

Qm- the maximum allowable pressure in the heating system. It will be determined by the threshold of the safety valve in the "safety group", which must be indicated in the product passport.

Qb- pre-pumping pressure of the air chamber of the expansion tank. It can also be indicated on the packaging and in the product documentation. It is possible to change it - pumping with a car pump or, conversely, bleeding through a nipple. It is usually recommended to set this pressure within 1.0 - 1.5 atmospheres.

Expansion tank volume calculator

To simplify the calculation procedure for the reader, a special calculator is placed in the article, in which the indicated dependencies are included. Enter the requested values, and after pressing the "CALCULATE" button, you will receive the required volume of the expansion tank.

The efficient operation of the heating system is possible due to the movement of the coolant, which constantly moves through the pipes. When a liquid is heated or cooled, it increases or decreases in volume. Expansion tank for heating allows you to increase the water capacity in the system during heating without fluid leakage.

How it works and what is it for

As we have already said, the compensation tank is needed for the efficient uninterrupted operation of the heating system. This device collects the liquid expanded as a result of heating, prevents accidents and leaks. During cooling, the coolant is evenly distributed through the pipes.

In the absence of an expansion tank, the working pressure will rise to a critical point of 3 atmospheres, as a result of which the emergency valve will operate and excess fluid will be discharged. In addition to the heating system, the expansion tank is used in hot water supply.

After use hot water from the boiler, this appliance will fill with cold liquid. During heating, she will have nowhere to go and an accident will happen. Compensation capacity and serves to prevent such accidents. An emergency valve can be used instead of a tank in a hot water supply system, but frequent switching on of it leads to a leak and damage to the device.

The main functions of the expansion tank are:

Collection of excess coolant;
Filling pipes with water when there is a lack of liquid;
Collection of accumulated air or water vapor, which is released as a result of the operation of the heating system;
Balancing the working pressure by increasing or decreasing the liquid volume.

The scheme of the expansion tank

At the moment, on the construction market you can find many different models of expansion tanks. All these devices can be divided into two types: open and closed. Despite the external similarity, the installation of these devices is carried out using different technologies.

Note! Open-type expansion tanks are used less and less, they are inefficient, they need to be constantly topped up with coolant. Closed compensation tanks differ from analogues in compact overall dimensions. Such devices work without human intervention.

Volume calculation

The process of calculating the volume of expansion tanks of open and closed type is somewhat different. The tank for an open heating system is made of sheet metal. There is a hole in the tank for supplying coolant to the system.

Such devices may also have another hole, which is located in the upper part and serves to drain excess fluid into the sewer. In some cases, the coolant (water) is supplied to the open expansion tank automatically, as it decreases.

When designing a heating system, it is important to calculate the volume of the compensation tank. The main value from which all calculations are based is the total volume of water in the system, e.g. 100 liters.

Note! When calculating the volume of an open-type expansion tank, a value of 10% is taken in relation to the total amount of coolant in the system. In our case, we need a 10 liter tank.

This calculation system, the so-called folk method, can also be used for closed-type expansion tanks. In addition, there is a more accurate method for calculating the volume of the tank. We will need the following data:

RH is the volume of increase in the coolant during heating. For water, this value does not exceed 5%, for antifreeze within 6%;
VK - the total volume of the coolant in the heating system circuit. The amount of water can be measured with buckets or using a special meter that is installed on the drain pipe;
DS - maximum pressure in the circuit and boiler (such information is provided in the instructions for the heater);
DB - pressure in the expansion tank.

To accurately calculate the volume of a closed expansion tank, the following formula is used:

V \u003d OV * VK * (DK + 1) / DS - DB

If we compare the result of the volume of the expansion tank calculated by folk method with the value obtained from the formula, then the second result will be less. If the tank size is slightly larger than the required value, the correct setting is necessary, which will contribute to the efficient operation of the device.

Pressure

Determining the volume of a closed expansion tank is considered important, but not the main aspect correct operation heating system. This device consists of two parts connected by a rubber gasket. Air and water, which are in these two reservoirs, do not contact. A nipple is installed in the air tank through which oxygen is pumped and the necessary pressure is created.

In the process of heating, the liquid fills one of the chambers of the tank. Given that high blood pressure in the air tank, the rubber gasket will not be deformed. This leads to the fact that the compensation tank does not perform its functions.

Note! For proper operation of the heating system, the air chamber of the expansion tank is pumped to a pressure that is 0.2 atmospheres less than the water pressure in the system. Such operations are carried out before the coolant is injected. Through a special nipple, pressure is added or bled to a pressure gauge of 1.3 atmospheres, at a pressure of 1.5.

The principle of operation of the expansion tank

In the hot water supply system, the pressure of the air chamber of the tank is set to 0.2 atmospheres more from the upper level of the pump.

Open type plastic heating tank

Metal is considered the standard material for an expansion tank, but such containers often corrode when exposed to air and water. The way out of this situation is to install a plastic tank, for example, a plastic 20-liter canister with a cut bottom, or a plastic bucket.

In the lower part of such a container, a crane is installed on an elastic band, then a piece of hose is fixed, which is securely fixed in a metal pipeline.

Installation in a closed heating system

According to experts, the installation of such a device can be carried out at any point in the heating system, but it is best to fix the expansion tank on the pipeline in front of the circulation pump.

Note! There is an exception to this rule: the tank cannot be installed after the pump or immediately after the boiler, because excess pressure will accumulate in it.

The tank can be mounted in any position, but the top location of the air chamber is considered the best option. In this case, air bubbles will tend to rise. They will not get into the coolant, which will prevent the occurrence of emergencies even if the gasket is damaged. To remove accumulated air in a closed heating system, a special valve is provided.

The device is fixed on the pipe using fittings on the tee, before the tank and then install a tap. It is necessary for checking and servicing the device before starting the heating system. To determine the serviceability of the tank, turn off the tap, turn on the heating and observe the readings of the pressure gauge.

When the arrow reaches one, open the valve and look at the pressure gauge dial. If the tank is in good condition, the pressure should drop to 0.2 atmospheres. This is due to the displacement of excess fluid.

During the operation of the heating system, there are cases when the volume of the compensation tank is not enough for effective work heating. In this case, there is no need to remove the tank and replace it with a larger tank. It would be more appropriate to install additional capacity.

Scheme of connecting an expansion tank to a closed-type heating system

If the expansion tank is installed in a heating system with natural circulation of the coolant, then a steam valve is required here. The main task of such a device is to relieve excess pressure that occurs when the liquid is heated above the recommended temperatures.

Installation in an open heating system

Note! The expansion tank is installed in an open-type heating system at the top of the circuit, at the highest point. Often such tanks do not have a top cover.

Water or other coolant in such a device has direct contact with air, which is considered the main disadvantage of such a system. The fact is that a high concentration of oxygen often leads to the destruction of the metal walls of the pipe.

A properly installed expansion tank reacts to changes in the water level, effectively removes accumulated air, because oxygen will tend to rise. Circulation pumps rarely installed in such heating systems. The coolant here moves slowly, by gravity, so the pipes must be exposed at a certain slope.

Installation diagram of the expansion tank in an open heating system, where it is located at the highest point

In practice, there are several ways to install an expansion tank:

On the flow in the upper part of the circuit above the boiler. In this case, the coolant in the tank will have a maximum temperature. The operation of the system is accompanied by quiet sounds, reminiscent of boiling water;
To prevent problems of extraneous noise, a compensation tank is installed on the return line.

The combined method involves the installation of two tanks: on the supply and return pipelines.

A device such as a membrane expansion tank of a heating system is used to compensate for changes in water volumes. Such changes are usually caused by its heating. The body of the membrane expansion tank of the heating system is divided into two parts by an elastic membrane. In one of them - a liquid substance, in the second - a gas. The first part is coolant, and the second is filled with air under high pressure or nitrogen.

Membrane expansion tank of the heating system

Where membrane expansion tanks are used and their advantages

Membrane tanks are used in the following areas:

Heating systems with autonomous heat sources;
Heating systems that are connected to centralized heat supply networks according to an independent scheme;
In systems using solar collectors and heat pumps;
They can also be used in other systems where there are closed circuits and a variable temperature of the working medium.

There are several advantages to using membrane tanks. Among them:

The suitability of membrane tanks for absolutely any water - even if it contains a lot of calcium;
Suitability of butyl and natural rubber membranes for drinking water applications;
Ease of membrane replacement;
A membrane tank, in comparison with a pressure tank without a membrane, has a large displaced useful volume;
There is no risk of contamination of drinking water;
No loss of coolant to evaporation;
Air pumping is minimal;
Mounting such a tank is economical and relatively fast;
Operating costs are low.

Peculiarities

The membrane expansion tank of the heating system will show the purpose of the tank: at all stages of operation, it must regulate the balance of the pressures of the cavities and compensate for excessive pressure or even its differences in the heating system. Thus, the membrane tank prevents increased loads in the heating system circuit, and, accordingly, emergencies with malfunctions.

The membrane tank for heating can be with a replaceable and non-replaceable membrane. The main feature of the first type is that the heat carrier is completely located in the flexible container of the membrane, thus not being able to interact with the inner steel surface. All actions for the installation and dismantling of the membrane are carried out through the flange, which is bolted.

If you have a tank with a fixed diaphragm in front of you, then it will have an internal cavity divided into two parts. The membrane in this case is diaphragmatic, non-replaceable and rigidly fixed.

Of course, the choice of a membrane tank for heating should be made exactly for a specific system, it depends on the amount of coolant.

If your expansion tank has insufficient volume, then this can lead to negative consequences - the appearance of cracks, the flow of hot water through the threads. Also, the pressure in the system may decrease below the minimum allowable, because of this, air can get inside the tank. That is why the choice of tank should be based on its exact compliance with the maximum possible parameters pressure.

The membrane expansion tank for heating is used in a closed liquid circulation system in order to compensate for the thermal expansion of the heat carrier due to changes in the temperature of the liquid, maintain the optimum pressure of the heat carrier and prevent hydraulic shocks. The water chamber and the gas chamber in constant mode have the same pressure, so the tightness in the system is not violated.

Water circulates without impurities of oxygen and other aggressive gases, so there will be no corrosion of the tank, which will allow it to work for a long time. The pressure expansion tank is located in the boiler room. Therefore, it does not require frost protection.

Expansion heating tank in the boiler room

The choice of tank is individual for each system, but, in general, several features must be taken into account. The initial pressure in a device such as a membrane heating tank that is connected to a cold system should be equal to the static pressure in the system plus 30-50 kPa. In addition, a reserve volume of heat carrier must enter the tank, which is required to compensate for leaks.

Also, the expansion tank must be selected so that, when taking the maximum increase in volume corresponding to the maximum temperature of the heat carrier, the pressure does not exceed the maximum allowable value.

To protect the system with a closed circuit and a tank from overpressure, safety valves must be installed.

Installation of a membrane expansion tank

Membrane expansion tanks are first supplied with an excess initial gas pressure, it fills the entire volume with itself. Before installing the expansion tank, it must be inflated to the pre-calculated pressure. A safety valve must be installed. It is also recommended to install a drainage device in front of the tank.

Installation instructions for the expansion tank must be included in the technical documentation. Yes, and to install, as a maximum, a specialist should, at least, it is best to consult with him on this important issue. When installing the tank, there are a few things to consider:

It is best if the tank is installed before the branching of the water supply. The room should be able to drain water and feed the system. Since freezing of water is unacceptable, the temperature in the room must be above 0.
The place where you are going to mount the tank must be load-bearing, since the tank should not receive additional load from other devices, pipes, etc. If you have a tank with a volume of 8-30 liters, then it is mounted on the wall, and if this volume is larger, then it is placed on legs.
Before installation, make sure that the calculations are correct!
The tank must be grounded so that there is no electrolytic corrosion process.
At the entrance to the tank you need to put check valve if it is not in the pump design. At the outlet - a device such as a pressure gauge to be able to control the pressure and an automatic valve to release air.

If there is no shut-off valve in the tank, then you need to put it at the installation site.