Heating is a key life support system for a private house and its stable operation is very important. One of the parameters that needs to be monitored is pressure. If it is too low, the boiler will not work; if it is too low, the equipment will wear out too quickly. An expansion tank for heating is required to stabilize the pressure in the system. The device is simple, but without it the heating will not work for a long time.
What is an expansion tank for heating for?
When the heating system is operating, the coolant often changes its temperature - it heats up, then it cools down. Understandably, the volume of the liquid changes. It increases and decreases. Excess coolant is just displaced into the expansion tank. So the purpose of this device is to compensate for changes in the volume of the coolant.
Types and device
There are two hot water heating systems - open and closed. In a closed system, the circulation of the coolant is provided by a circulation pump. It does not create additional pressure, it simply pushes water at a given speed through the pipes. In such a heating system, there is an expansion tank for closed-type heating. It is called closed because it is a sealed container, which is divided into two parts by an elastic membrane. In one part there is air, in the other excess coolant is displaced. Due to the presence of a membrane, the tank is also called a membrane one.
An open heating system does not provide for a circulation pump. In this case, an expansion tank for heating is just any container - even a bucket - to which the heating pipes are connected. It doesn't even need a cover, although it might be.
In the simplest version, this is a container welded from metal, which is installed in the attic. This option has a significant drawback. Since the tank is leaking, the coolant evaporates and it is necessary to monitor its amount - top up all the time. You can do this manually - from a bucket. This is not very convenient - there is a risk of forgetting to replenish water supplies. This threatens the system with airing, which can lead to its breakdown.
Automated control of the water level is more convenient. True, then in the attic, in addition to the heating pipes, you will also have to pull the water supply and also take out the overflow hose (pipe) somewhere in case the tank is overfilled. But there is no need to regularly check the amount of coolant.
Volume calculation
There is a very simple method for determining the volume of the expansion tank for heating: 10% of the volume of the coolant in the system is calculated. You had to calculate it when developing the project. If these data are not available, you can determine the volume empirically - drain the coolant, and then fill in a new one, while measuring it (put it through the meter). The second way is to calculate. Determine in the system, add the volume of radiators. This will be the volume of the heating system. Here we find 10% of this figure.
Formula
The second way to determine the volume of the expansion tank for heating is to calculate it using the formula. Here, too, the volume of the system will be required (indicated by the letter C), but other data will also be needed:
- maximum pressure Pmax at which the system can operate (usually the maximum boiler pressure is taken);
- initial pressure Pmin - from which the system begins to work (this is the pressure in the expansion tank, indicated in the passport);
- coefficient of expansion of the heat carrier E (for water 0.04 or 0.05, for antifreeze it is indicated on the label, but usually in the range of 0.1-0.13);
Having all these values, we calculate the exact volume of the expansion tank for the heating system using the formula:
The calculations are not very complicated, but is it worth messing around with them? If the system is open, the answer is unambiguous - no. The cost of the container does not depend very much on the volume, plus everything you can do it yourself.
Expansion tanks for closed-type heating are worth counting. Their price depends on the volume. But, in this case, it is still better to take with a margin, since insufficient volume leads to rapid wear of the system or even to its failure.
If the boiler has an expansion tank, but its capacity is not enough for your system, put a second one. In total, they should give the required volume (the installation is no different).
What will the insufficient volume of the expansion tank lead to?
When heated, the coolant expands, its surplus ends up in the expansion tank for heating. If all the excess does not fit, it is vented through the emergency pressure relief valve. That is, the coolant goes down the drain.
Then, when the temperature drops, the volume of the coolant decreases. But since there is already less of it in the system than there was, the pressure in the system drops. If the lack of volume is insignificant, such a decrease may not be critical, but if it is too small, the boiler may not work. This equipment has a lower pressure limit at which it will operate. When the lower limit is reached, the equipment is blocked. If you are at home at this time, you can remedy the situation by adding a coolant. If you are not there, the system may unfreeze. By the way, working at the limit does not lead to anything good either - the equipment quickly breaks down. Therefore, it is better to play it safe a little and take a slightly larger volume.
Tank pressure
In some boilers (usually gas ones), the passport indicates what pressure must be set on the expander. If there is no such record, for normal operation of the system, the pressure in the tank should be 0.2-0.3 atm lower than the operating pressure.
The heating system of a low-rise private house usually operates at 1.5-1.8 atm. Accordingly, the tank should be 1.2-1.6 atm. The pressure is measured with a conventional manometer, which is connected to the nipple, which is located at the top of the tank. The nipple is hidden under a plastic cover, you unscrew it, you get access to the spool. Excess pressure can also be relieved through it. The principle of operation is the same as that of an automobile spool - bend the plate with something thin, releasing the air to the required values.
It is also possible to increase the pressure in the expansion vessel. This will require a car pump with a pressure gauge. Connect it to the nipple, pump it up to the required readings.
All the above procedures are carried out with the tank disconnected from the system. If it is already installed, you do not need to remove it. You can check the pressure in the expansion vessel of the heating system on site. Just be careful! It is necessary to check and adjust the pressure in the expansion tank for heating when the system is not working and the coolant is drained from the boiler. For the accuracy of measurements and tank adjustment, it is important that the pressure on the boiler is zero. Therefore, we drain the water thoroughly. Then we connect the pump with a pressure gauge and adjust the parameters.
Where to put in the system
An expansion tank in a closed system is placed after the boiler before the pump, that is, so that it creates a flow in the opposite direction. This makes the system more reliable. So the exact place of installation depends on where you have the circulation pump.
It is connected to the system through a tee. You cut a tee into the pipe, direct the perpendicular outlet upward, the tank is screwed onto it. If the wall does not allow the container to be placed, you will have to make a knee, but the tank is turned up. You can now assume that the expansion vessel is installed.
But for the convenience of checking, it is advisable to put another tee after the tank, on the free outlet of which to install a shut-off valve. This makes it possible to check the membrane tank without draining the entire system - it cuts off the tank. Turn off the tap, bleed water from the boiler. Check the pressure on the disconnected branch (in the boiler). It should be zero. After that, you can carry out all the rest of the configuration work.
The diaphragm expansion tank is an indispensable component of the heating system, without which it is impossible to fully heat the room in the cold season. With the help of this device, critical changes in the volume of water are compensated, which are the result of its heating.
Tank device
If the heating system does not include an additional device, into which an excess volume of liquid can pass, then it may fail. The role of a spare tank is played by a membrane tank, which is necessary for smooth operation.
Membrane
The reservoir housing has an elastic membrane that divides its inner chamber into two parts. One part contains a coolant, and the other is filled with air. Nitrogen can be used instead.
Depending on the model, the device may include a replaceable or non-replaceable membrane. In the first case, the coolant is placed in an elastic cavity and does not come into contact with the metal inner surfaces.
Installation (or removal) of the membrane is carried out through the flange, for which bolts are used. Such manipulations are performed when the equipment is being repaired.
If the device has a non-replaceable membrane, then it is equipped with an internal cavity of two sections. Dismantling in this case is not provided.
To protect the system from overpressure, the diaphragm tanks are equipped with safety valves.
Operating principle
The principle of operation of the device is based on the change in the volume of liquid during heating and cooling.
In a closed loop, the water, heating up, expands, while the pressure in the entire network increases. The excess volume of liquid enters the expansion tank, where it reduces the amount of air by stretching the membrane between the chambers. 
As the temperature drops, the pressure in the system drops and air displaces water from the tank. Water from the tank will continue to flow until the pressure equilibrates.
Application area
Diaphragm tanks are widely used. They are embedded in systems such as:
- heat supply with an autonomous heat source;
- heating system connected to the central heating line according to an independent scheme;
- heating powered by solar collectors and heating ducts;
- any systems with a closed loop and variable temperature of the working environment.
Advantages
The invention of a closed expansion tank with a membrane made it possible to increase the working life of the entire heating system. The device has the following advantages:
- allows the use of water of any composition, incl. hypercalcified;
- a membrane made of butyl and natural rubber allows the use of equipment for drinking water;
- the principle of operation and the membrane design of the device can ensure the reception of a significant amount of the displaced liquid;
- easy installation;
- minimal losses from evaporation;
- low operating costs.
Scheme of use in the heating system.
The compact dimensions of the flat membrane tank allow an economical use of room space, so it is best suited for oversized rooms.
The expansion tank does not allow the occurrence of increased loads in the heating system and is an effective means of preventing emergencies.
Equipment selection
First of all, the volume of the coolant for the heating system is taken into account. If the selection is not performed correctly and the volume is not enough, then cracks and water leaks will appear at the joints.
In addition, pressure may drop below a safe minimum. This will lead to the airing of the internal cavity of the tank, then urgent repairs will be required. Therefore, it is better to select a model based on the characteristics that the accompanying instructions contain.
The value of the initial pressure in the expansion vessel connected to the cold heating network must match the static pressure of the system. The permissible discrepancy between the indicators can be + 30-50 kPa.
This table will help you calculate the required tank volume.
The tank must have a volume of at least 10-12% of the total volume of the heat supply network in which it is used. This will exclude the possible failure of both the reservoir itself and the entire heating system as a whole during a pressure surge.
When choosing a suitable model, you should also take into account the maximum allowable pressure at which the device can function.
Diaphragm tanks protect the heating system from excessive temperature rise and regulate the pressure level in it. Therefore, such devices are equipped with independent temperature and pressure sensors.
Mounting the device
The installation is carried out in such a way that subsequent maintenance can be carried out without hindrance.
The new tank, as a rule, has an excess initial gas pressure that spreads throughout the entire volume. Before installing the expansion tank, it must be inflated to the previously calculated pressure.
The diaphragm tank must be installed before branching the water supply. It is necessary to ensure the drainage of water and make-up of the system. The room must be maintained at a positive temperature.
Additional loads on the tank are unacceptable! If the container has a volume of 8 to 30 liters, then wall mounting is allowed. For large volumes, the equipment is placed on its legs.
Grounding must be carried out to prevent electrolytic corrosion.
Setting up the device
In order not to wonder how to check the pressure, it is advisable to install a pressure gauge at the outlet. To remove excess air, it is rational to supplement the equipment with an automatic valve.
The set of the required pressure is carried out in strict sequence. First, the pressure is released through the nipple or using a compressor. Then connect the device to the heating system and fill it with water. The process does not stop until the pressure in the system and in the tank is the same.
In an autonomous heating system, there is always an expansion tank for heating, or a compensator. Its function is to compensate for the excess pressure that occurs in the system when the heat carrier expands due to heating. With a rapid increase in temperature, the heat transfer fluid expands and a pressure surge occurs, the so-called water hammer. It can destroy pipeline elements and fittings. Other names for the expansion device: hydraulic accumulator, expansomat.
The device and principle of operation of expansion tanks for heating
Heating systems are open and closed. Accordingly, expansion tanks for heating exist of an open type and a closed one.
Open type tanks
An open expansion tank for heating is a parallelepiped-shaped container made of stainless steel. Such a tank is placed at the highest point of an open heating system, usually in the attic.
Pipes are connected to the tank:
- trunk;
- circulating;
- signaling, with a locking device.
In a heating system of this type, the coolant (water) circulates naturally, without pumps. Despite the relative cheapness and simplicity of such heating, it is gradually becoming a thing of the past due to numerous shortcomings.
- In an open tank, the coolant constantly evaporates, so you need to control the water level and add as needed. For the same reason, it is problematic to use another coolant, for example antifreeze - it evaporates even faster.
- Overflow of water from the tank is possible, therefore, it is necessary to provide for its drainage into the sewer or drainage.
- An open expansion tank requires good thermal insulation so that the water does not freeze in severe frosts.
- Additional pipes and fittings are required for installation in the attic.
- Air entering the system from the expansion device provokes corrosion of the piping and radiators, and also leads to the appearance of air pockets.
The open expansion joint system is suitable for heating small one-story houses. Larger houses are heated by closed systems.
Closed tanks
A closed or membrane expansion tank of a heating system contains an elastic membrane inside that divides the internal volume of the expansion tank into two compartments, gas and liquid. The gas part contains air under pressure (in some models - nitrogen or inert gas), and the liquid part contains excess coolant when heated.
Closed tank (membrane)
The higher the temperature, the more the liquid part of the accumulator is filled. At the same time, the gas part is reduced and the pressure in it increases. When the threshold value is reached, the safety valve is triggered, excess pressure is released. And when the heating system cools down, the reverse process takes place, and the coolant returns from the tank to the pipeline.
The principle of operation of the diaphragm expansion tank
There are two types of membrane expansion joints.
- With a diaphragm-type membrane. These are small tanks. The diaphragm membrane in them is non-removable and cannot be replaced: if it breaks, you will have to completely change the device.
- With a balloon (pear-shaped) membrane. It can be changed when worn and is used in large 1000 liter tanks.
The volume of expansion tanks for heating can vary widely from two to several thousand liters. The shape of the closed accumulator is flat or cylindrical. In a flat expansion tank, the diaphragm-membrane is located vertically, in a cylindrical one horizontally.
It is worth paying attention: the membrane expansion joint is sometimes mistakenly called a vacuum expansion tank for heating. However, this device does not use vacuum. The heating system may have a vacuum deaerator to remove air microbubbles from the water.
Installing a diaphragm expansion tank
Unlike an open one, a membrane accumulator can be installed for ease of maintenance right at the heating point, next to the boiler. Usually it is placed in a straight section in front of the circulation pump, preferably so that water (or another heat carrier) enters the expansion joint from above. It must be equipped with a pressure gauge, a safety valve and connected to the return line.
Hydraulic accumulators with a volume of up to 30 liters are mounted on the wall, larger ones are installed on the floor. When mounted on a wall, the tank must be securely fastened, as its weight increases dramatically when filled with water.
Several membrane tanks in a heating station
Important performance data and calculation of the expansion joint volume
When selecting an expansion vessel, take into account the maximum operating temperature and pressure. For example, the heating medium can be heated up to + 120 ° C, and the peak pressure in the heating expansion tank can reach 6-10 bar (the usual average value is 2-4 bar). Therefore, the characteristics of the membrane, its durability, heat resistance, and compliance with sanitary standards are important.
The volume of the expansion joint depends on the volume of the heat carrier as a whole in the system. It is not necessary to calculate the volume mathematically accurately, a simplified method is often used: a tank with a capacity equal to 10% of the total volume of the coolant is chosen. And if this volume is unknown, then they proceed from the power of the boiler and the type of heating devices. The ratios are as follows: for heating batteries - 11 l / kW, for underfloor heating - 17.5 l / kW, for wall-floor heaters - 7.5 l / kW.
If the capacity of the selected expansion joint is found to be insufficient, the relief valve will relieve pressure too often. In this case, it is enough to purchase and connect in parallel another expansion tank.
It is quite difficult to take into account all the nuances, especially since in every house the heating system necessarily has its own characteristics. In order not to be mistaken when choosing and installing a device, it is better to contact a specialized company.
Video: installation of an expansion tank
Diaphragm expansion vessel for closed heating systems
The diaphragm expansion tank is designed to compensate for the thermal expansion of the coolant and maintain the required pressure in closed heating systems.
Fluids that are used in heating systems, when heated, due to thermal expansion, increase their volume. 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, then the volume of the liquid increases even more.
Diaphragm expansion tank for heating. Device and scheme of work. Through the air valve (nipple), the air chamber is filled with compressed air with an automobile pump.
In a closed heating system without an expansion vessel, even a slight increase in temperature will lead to a sharp increase in pressure and trigger the safety valve. The excess part of the coolant will pour out through the valve.
The diaphragm 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 a coolant. Air is pumped into the other part of the vessel under a certain pressure.
When the volume of liquid in the heating system changes, the membrane in the tank moves to one side or the other. As a result, the volume occupied by the liquid in the tank also changes. The compressed air on the other side of the diaphragm acts like a spring, maintaining the operating pressure of the heating medium and preventing the safety valve from opening.
Operating limits 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 heating fluid in the heating system. For example, the content of ethylene glycol in the antifreeze solution is limited.
It is forbidden 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 imperative to install a safety group that monitors and limits the pressure in the tank.
In the heating systems of private houses and autonomous heating of apartments, tanks and other heating equipment with a working pressure of at least 3 bar.
The expansion tank for heating is not allowed to be used in drinking water supply systems.
Installation, assembly and connection of the expansion tank
The expansion tank is connected to the return pipe of the heating system from the suction side of the circulation pump. 1 - membrane expansion tank; 2 - connecting shut-off valves and drain cock; 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. The installation is carried out so that there is access to the air nipple, flange and fittings.
Small expansion tanks are usually attached to the wall with a bracket. Fastening parts, as a rule, are not included in the product set and must be ordered separately. Large tanks are installed on the floor, on legs.
The expansion tank is connected to the return pipe of the heating system from the suction side of the circulation pump.
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 point of connection, on the line to the tank, it is necessary to install shut-off valves protected from accidental closing. In addition, a drain valve should be installed to empty the tank. Tank manufacturers usually offer special fittings for their products. These kits must be ordered separately.
To connect the tank to the return pipe, use pipes with an inner diameter equal to the diameter of the tank connection.
The expansion tank is connected to the heating system after flushing the system.
Built-in diaphragm expansion tank is located on the back wall of the double-circuit gas boiler Diaphragm expansion vessels 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 pipe. The volume of the new tank is selected as usual, without taking into account the capacity of the built-in tank.
Expansion vessel pressure setting
Before commissioning the heating system, before filling the tank with coolant, air is pumped into the expansion tank through an air valve - a nipple with a car pump. The value of air pressure is controlled by an automobile pressure gauge built into the pump or by 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 the sufficiency of the initial air pressure in the tank.
Initial pressure in the air chamber expansion tank - P about :
P o> P st + 0.2 bar ,
where P st- the static pressure of the heating system at the place where the tank is installed is equal to the height of the water column from the connection point of the expansion tank 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. if there is no liquid in the tank- open the connecting nipple and pour out the rest of the coolant from the tank. 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 factory filling of the air chamber with air or nitrogen pressure P about = 0.75 - 1.5 bar ... This value of the pressure set at the factory can be left unchanged, even if it is significantly higher than that calculated by the formula P about... In most cases, this pressure is sufficient for heating systems of a private house or apartment.
The expansion tanks built into the boiler are usually already filled with air or nitrogen up to the pressure specified in the boiler manual. 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 the air.
Exceeding the initial pressure over the static pressure by at least 0.2 bar. it is necessary to create pressure in the system, at which the risk of vacuum formation, vaporization and cavitation is reduced.
In the next step the tank is connected to the heating system. Then the make-up valve opens and the heating system and the tank are filled with coolant with the initial make-up pressure - P start.:
P start> or = P about + 0.3 bar
(for example, if P o = 1 bar, then P start> = 1.3 bar)
P about- the 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 of the heating medium in the system. The instructions also indicate the minimum pressure of the coolant, below which the boiler simply will not turn on. In this case, the system is filled with the initial pressure specified in the instructions for the boiler.
Further, turn on the boiler and heat up the heating system to the maximum operating temperature (for example, 75 o C). When heated, the air dissolved in it is released from the water. We remove air from the heating system. We follow the readings of the manometer and record the pressure 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 - P con:
P con< или = Р кл — 0,5 bar ,
where R cl- opening pressure of the safety valve of the heating system.
(for example, if P cl = 3 bar, then the pressure in the system is brought to P con<= 2,5 bar at a coolant temperature of 75 o C)
The method described above for setting the expansion vessel pressure allows the effective usable volume of the expansion vessel to be raised to the maximum. The tank will be able to take in the largest amount of water, and then give it back to the system. This is useful in the case of, for example, small leaks in the system. The tank will be able to give water to the system for a long time - the pressure in the system will decrease at a slower rate. The efficiency of the heating system will be maintained for a longer time. Or, as a result of cooling 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 heating. When adjusting the pressure according to the above method, the risk of such a development of events is reduced to a minimum.
These advantages, described here, the pressure setting technique are especially relevant for heating systems in country houses, where the owners do not look every day.
Diaphragm integrity check
Briefly operate the air valve (nipple). If water flows out of the valve, the tank must be replaced, or, in tanks with a replaceable diaphragm, the diaphragm must be replaced.
If it is necessary to remove gas from the air chamber of the expansion tank, it is imperative to empty its water chamber before doing this, 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 so that when the heating medium heats up to the maximum operating temperature, the pressure rise in the heating system does not exceed the permissible value (remains below the response pressure of the safety valve).
The volume of the expansion tank for the heating system 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 chosen according to a simplified formula:
V n = 10 - 12% x V s ,
where: V n- the estimated volume of the expansion tank; V s- the total volume of the heating system.
Calculation of the capacity of the expansion tank for a heating system with a volume of more than 150 liters
The calculation begins with determining the increment in the volume of the coolant - the additional volume that is formed as a result of heating the liquid to the operating temperature - V e.
V e = V s x n%,
where, V s- the total volume of the heating system; n% Is the coefficient of expansion of the liquid in the heating system.
Expansion coefficient value n%, at the maximum operating temperature of the heat carrier (water) in the heating system, is determined from the table:
| T o C | 40 | 50 | 60 | 70 | 80 | 90 | 100 |
| n v% | 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 n v%- coefficient of expansion of water from the table above; e a%- the percentage of ethylene glycol in the antifreeze solution.
At the second stage of the calculation(by the second step) determine the volume of the water seal in the tank, V v- This is the volume of the coolant that initially fills the expansion tank under the influence of static pressure in the heating system. The capacity of the water seal is determined by the formula:
V v = V s x 0.5%, but not less than 3 liters.
In the third stage we 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 of 1 bar= 10 meters of water column. The height of the water column in the heating system is equal to the vertical distance between the lowest point and the highest point of the system in which the coolant is located. According to the drawings or in kind, the vertical marks of the extreme points of the heating system are determined. The difference between the upper and lower marks will be equal to the height of the water column in the system.
In the fourth stage calculations determine the value of 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 necessarily P k - P e => 0.5 bar .
where: P k- pressure of the safety valve.
At the conclusion of the calculation determine the required volume of the membrane expansion tank for heating by 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.
An example of calculating an expansion tank
Let's calculate the expansion tank for the heating system with the initial data:
Overall volume V s = 270 l.
Height of water column 6 m., hence the initial pressure P o = 6/10 = 0.6 bar.
Maximum operating temperature of the heat carrier (water) 90 o C... Determine the expansion coefficient from the table n% = 3.55%.
The safety valve is set to operate at pressure P k = 3 bar .
We make a 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 is obligatory, then we take 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 volume, when choosing a specific type of expansion tank, the maximum operating pressure must be taken into account the tank is designed for.
The stability, reliability, efficiency and durability of the heating system depend on how correctly all its parameters are calculated, how harmoniously its devices, units and necessary devices interact with each other, how well the installation and adjustment are performed. And there can be no trifles in such matters.
It would be completely unreasonable to divide individual devices and nodes into "important" and "not so". Yes, the cost of elements can differ very significantly, the functionality of some is always in sight, while others are completely invisible and even incomprehensible, from the point of view of an inexperienced user... But each fulfills its own "mission" in the overall work of the system. Therefore, for example, the question looks completely amateurish - is the expansion tank so important for the heating system, and is it worth giving importance to the problem of its choice and correct installation? Meanwhile, the importance of this simple device is difficult to overestimate.
Why is an expansion tank necessary in principle?
This is the easiest question to answer. Even someone who did not study very well in high school probably knows simply from life experience - when heated, physical bodies increase in volume. And water is no exception in this regard.
It is interesting that water has another unique quality - it begins to increase in volume and when it cools below the threshold of +4 ° WITH, that is, during freezing - a transition to a solid state of aggregation. But this does not apply to the topic of our consideration now.
Thermal expansion is characterized by a special value - the coefficient. This, specifically for water, is a non-linear indicator that largely depends on temperature. The coefficient itself shows how many times the volume increases when the liquid is heated by 1 degree.
We will not present the entire table of coefficients for water here. It is better to illustrate this extension with a known physical experiment.
So, on the left side of the figure, a tank is shown, to which, up to the overflow hole, exactly 1 liter (1 dm³) of water with a temperature of + 4 ° is placed WITH... This value is the zero reference point for water. A measuring container is installed under the overflow pipe.
The water in the tank starts to heat up. With an increase in temperature, the density of water decreases, that is, while its mass remains equal, an expansion of the volume is observed. When heated to a temperature of + 90 ° WITH about 36 ml of water is collected in a measuring container - this is a volume that has become excessive and passed through the overflow pipe.
Is it a lot or a little? It seems to be nonsense. But if we look at it on a more serious scale, then with a change in temperature, very significant fluctuations in volume are obtained. Judge for yourself - with 100 initial liters, we would already be talking about 3.5 liters of excess.
If you leave water in a closed volume, then it will have nowhere to expand - it is an incompressible body. Therefore, according to the laws of thermodynamics, pressure begins to rise under such conditions. But this is already serious. If the pressure in the closed circuits of the heating system exceeds the permissible threshold, then it will still be a successful outcome if everything is limited to flow at the pipe connections or. But an uncontrolled increase in pressure can bring much more destructive consequences.
In order not to bring the situation to even minor accidents, an additional container must be provided in the heating system, which would be able to receive and give off excess water (or any other liquid heat carrier) formed during its heating. This is the task assigned to the expansion tanks. However, even their name speaks for itself.
With the generality of the main function, the design of the expansion tanks may differ. And the main difference lies in the features of the heating system itself, which can be open or
Expansion tank in an open-type heating system
The specifics of the location of the open tank
The features of such a system are probably already clear from its name. The circuit is, of course, closed, but it is not isolated from the atmosphere, leaking, and there can be no excess pressure in it, by definition. And the expansion tank is an ordinary container embedded in the circuit. The main condition is that it should be located above the highest point of the system.
Expansion tank prices
expansion tank
Why the highest point? Everything is simple - otherwise, the liquid will simply pour out according to the law of communicating vessels.
In addition, this arrangement contributes to the performance of another important function - the open-type expansion tank becomes an effective air vent. There is always dissolved air in water, which is able to pass into a gaseous state familiar to itself. In addition, chemical reactions between the coolant and the material of pipes and heat exchangers can lead to the release of gases. And the accumulation of gas can lock the radiator or even an entire section of the heating circuit. So the timely removal of gas bubbles is extremely important.
True, sometimes open expansion tanks crash into the return line (for one reason or another). But all the same - this is the highest point of the system, to which a vertical pipe is simply laid. In this case, the gas trap function does not work, and this will require the installation of additional valves on the radiators and, again, at the highest point of the system on the supply pipe.
Design options
What is the design of an open expansion tank? It can be the simplest one or have some improvements. In any case, this is a container of a certain volume, which is usually covered with a lid on top. The cover is only needed to protect against debris or dust entering the water, and is never sealed. That is, the current atmospheric pressure is always maintained in the tank. A v the container itself has nipples embedded - from one in the simplest version, to several, for various purposes.
Expansion tanks of an open type can be purchased ready-made - the stores offer a fairly wide range of products of various sizes. Most often they are made of stainless steel or galvanized steel sheet to prevent corrosion.
But many craftsmen prefer to make such tanks on their own. The container is quite possible from sheet material, and often ready-made ones are used - for example, metal or even plastic barrels or cans, old gas cylinders, etc. All this will cost very inexpensively, and it will not be difficult for a good owner to make an appropriate cut-in of the pipes.
Let's take a look at several possible layouts of such tanks:
The simplest scheme - a branch pipe is simply cut into the container from the bottom, which is connected to the heating circuit.
It is clear that with this design, there is no circulation of the coolant through the tank will not. When filling the system, ensure that the water level in the tank is approximately in the middle of its height. And fluctuations in the volume of liquid in the system will be reflected by an increase and decrease in this level.
Of course, control is needed over the level of the coolant in the tank - evaporation, one way or another, will be, and if you do not replenish the water, then you can cause an air blockage of the system circuit or "airing" of the radiators. So you will have to look into an expansion tank of such a simple design regularly in order to make recharge if necessary.
Various tricks are used to facilitate visual inspection. In particular, it is possible to embed from the side of the tank small diameter branch pipe, on which a short piece of transparent hose is put on. It is clear that the water level in the hose will correspond to the level in the tank - a quick glance is enough to assess the situation.
But it has already been said that the tank should be located at the highest point, and very often the attic becomes this place. That is, the container is not in plain sight, and it is extremely inconvenient to climb up every time to check the level. But this control can be organized in a different way. An example is shown in the diagram below:
Two branch pipes are cut into the tank from the front side.
The upper one (pos. 1) determines the maximum permissible filling of the container, and simply works for overflow. From it, a pipe (hose) is drawn into the sewer or even simply discharged onto the ground - into the garden.
A pipe is connected to the lower branch pipe (item 2), which goes into the room, on which an ordinary ball valve is located in a convenient place for the owners. The height of the embedded branch pipe determines the minimum permissible water level in the tank. That is, to control the fullness, you just need to open the tap - if water comes out of the pipe, then everything is normal. Otherwise, make-up is carried out until water flows through the overflow pipe.
Convenient for punctual owners who remember the need for regular monitoring. But for the forgetful and such a scheme is unlikely to become a "helper". But it is quite possible to "automate" the process of maintaining the level in the tank at the required level. To do this, it will be enough to bring a make-up pipe (from the water supply) to the tank, but connect it through a float valve, which is usually used in toilet flush cisterns.
That is, the overflow pipe will protect against overflow (it is necessary in any case), and such a simple make-up system will not allow a critical drop in the level.
All the schemes shown above can be figuratively called "passive" - the coolant does not circulate through the expansion tank. This simply creates free space for the expanding volume of liquid. It is not difficult and quite efficient. But there is also a drawback - the function air vent in such tanks is very unproductive. A considerable amount of air bubbles, entrained by the flow of water when following the supply line, will simply slip past the place where the branch pipe is connected to the expansion tank. And in order for the tank to become an effective air separator, circulation is often closed through it. That is, it becomes a link in the general water circulation loop.
It might look something like this:
The coolant is supplied to the tank through a pipe 1 , and through the branch pipe 2 it enters the supply line again. A sharp increase in volume (at the transition from the pipe diameter to the tank), accordingly, causes a sharp decrease in the flow rate, which contributes to the ascent and release of the smallest gas bubbles into the atmosphere. Pipe position 1 it can be different, for example, it can be supplied from below. But in any case, its welded pipe inside the tank should be located above the outlet
Overflow pipes (pos. 3) and make-up in such circuits are no different from the options shown above. It's just that not everything is indicated here, so as not to overload the picture.
Of course, if such an expansion tank connection scheme is used, then steps are being taken for its very high quality thermal insulation. Otherwise, completely unproductive and very large heat losses are possible, especially if the tank has to be located in an unheated room.
By the way, the scheme shown above can have further development. You can find examples when the function of the distributing manifold is also assigned to the expansion tank, if the heating system is organized according to the principle of risers.
In this case, they try to place a well-insulated tank as close as possible to the geometric center of the house. And already from it, the hot coolant is dispensed along the risers of the system through the embedded nozzles.
How much tank volume is required?
Now about what should be the volume of an open expansion tank. There are no strict rules on this matter. Everyone can, knowing the value of the coefficient of thermal expansion of water, the capacity of their heating system and its expected temperature mode of operation, estimate how much the volume of liquid will increase.
Based on the above values, one would assume that since heating 100 liters of water to 90 degrees gives an increase in volume of 3.5 liters (that is, in fact, 3.5%), then one can proceed from the norm of 5% of the system capacity. But practice shows that this is clearly not enough. Do not forget that the tank must be pre-filled to at least a quarter of its height (this is the minimum) - so that the system does not "grab" a portion of air. Further, the same "variable volume" is provided, which will compensate for the expansion. Approximately at the upper boundary of this volume, an overflow pipe is cut. Well, above the water level, there must be free space to the lid. That is, you cannot keep up with 5 percent.
The experience of the masters involved in the installation of heating shows that the best solution would be to proceed from the following approximate ratio: tank volume ≈ 10% of the system volume.
This means that you need to know the volume of your system. How do I find it?
- If the heating system is ready, then the easiest way will be to detect with a water meter how much will fit into it until it is completely filled. Reception is very accurate, but very little helpful. Agree, usually the capacity of the tank is calculated in advance, and not after the installation of the circuits.
- With a very large error, but still you can accept the ratio: 15 liters of water for each kilowatt of boiler output... It is clear that with this approach, it is not difficult to make a mistake.
- Finally, the volume of the heating system can be easily calculated. It must be assumed that if it is planned to install an expansion tank, then the system design already includes the mounted contours of pipes of one type or another, and the model of the boiler, and the types of heating radiators, and their number. That is, if you sum up the volumes of all elements of the system, you can find the desired value.
The task may seem daunting. But in fact it is not so scary - if you use our online calculator, to which the link leads (it will open on a separate page).
JILEX expansion tanks prices
expansion tank JILEX
How to calculate the total volume of the heating system?
The selection of an expansion tank is far from the only case when this parameter will become necessary. For example, this is required when buying antifreeze coolant, when carrying out some calculations of mixing units, etc. With our calculator calculation common volumeheating systems the reader will perform the calculations without much trouble.
Please note - if the calculations are made in order to determine the optimal volume of the expansion tank, then the tank itself should be excluded from the calculations. It's easy to do - just move the slider to the "0" position.
Disadvantages of an open heating system
So, let's summarize the expansion tank in open heating systems.
By the way, such systems completely prevailed not so long ago. If only for the reason that it was simply impossible to buy equipment for a closed-type system. But today, alas, they have to be recognized as obsolete.
- Explicit dignity simplicity of design is seen. In some cases, it is practically not necessary to purchase any additional materials at all. If desired, a completely functional tank can be made "on the knee" from the "trash" stored in the garage.
- In an open system, a priori, dangerous pressure cannot arise, since it is associated with the atmosphere. This obviates the need for a safety valve.
- We add to the advantages the ability of the expansion tank to act as air vent.
But disadvantages the open system also has quite a few:
- It has been noted more than once that the tank should be installed at the highest point in the system. It is good if the house has an insulated attic. But this does not always happen, and it is necessary to provide for a very high-quality insulation of the container, so that it simply does not "grab" in a severe frost.
- If the tank has to be installed indoors (for example, there is no attic at all), then it, placed under the ceiling, will clearly not become an interior decoration.
- The water level in the tank needs constant monitoring. This problem, as we have seen, is solvable, but nonetheless.
- Moreover, due to leaks, there is a constant process of water evaporation. The coolant from contact with air is saturated with oxygen, which activates corrosion on the metal parts of the circuit and in the boiler heat exchanger.
- If you have noticed, the discussion above was exclusively about water as a heat carrier. In open systems, it cannot be otherwise - the evaporation of expensive antifreeze looks wasteful. In addition, many antifreezes when evaporated are not at all safe for health. So if an open heating system is planned in a house that often remains empty in winter, you will have to drain the water from it.
- Such a system is not possible if an electrode boiler is used. Its work is based on the principle of electrical conductivity of the coolant, that is, the chemical composition is of great importance. And with uncontrolled evaporation, the optimal concentration will quickly be lost.
- A stable low system pressure is not always an advantage. Some heating devices, on the contrary, show their advantages precisely at increased pressure indicators.
As you can see, there are a lot of shortcomings. Therefore, a closed-type heating system is considered more perfect. But it uses a completely different expansion tank.
Expansion tank for closed heating system
The main advantages of such a tank can be considered its compactness and the ability to install on any part of the heating system. The fact that it is often drawn on diagrams mounted on a "return" pipe in the immediate vicinity of the pumping unit is, indeed, a recommended position. But there are no serious restrictions on the choice of another place.
Expansion tank prices Wester
expansion tank Wester
The fact that the tank is sealed means that the pressure in the system can rise to very significant levels. This predetermines the need for a "security group" in the loop. Such a group traditionally includes a safety valve set to a certain upper pressure threshold, automatic air vent and instrumentation - pressure gauge or pressure gauge combined with a thermometer.
It is unlikely that this can be fully attributed to the shortcomings - rather, these are the operational features of the system. So the only "disadvantage" of a closed expansion tank can be considered the need to purchase it. But it is not a sin to pay for the comfort in using the system.
By the way, many modern heating boilers, especially wall-mounted ones, are already initially equipped with a built-in expansion tank of the required volume. So you don't have to buy or install anything.
The device and principle of operation of the expansion tank for a closed heating system.
The tank device is pretty simple. The design may vary slightly, but the principle is the same in all models.
And the principle is that the hermetically sealed volume is divided into two chambers by an elastic partition. One chamber, water, is connected through a branch pipe to the heating system circuit. The second is air, in which a certain pressure level is preliminarily created.
The device can be illustrated by the following diagram:
The tank body (item 1) is usually a prefabricated stamped metal structure. The cylindrical shape is "classic" but there are other options, inside the walls are treated with an anticorrosive compound, a protective enamel coating is applied outside. The color should be red. The fact is that there are also accumulator tanks, which both externally and in their structure differ little from expansion ones. But their blue color suggests that they not calculated to work in high temperature conditions. So there is no complete interchangeability here.
There is always a threaded pipe (item 2) installed on the body, through which the expansion tank will be connected to the heating circuit. Some manufacturers immediately complete their products with fittings with an American union nut - so the process of installing the tank will be even easier.
On the opposite side of the body there is usually a nipple or spool (item 3), very similar to a bicycle one, through which the air chamber is pumped to the required pressure level in it.
The main part of this design is the diaphragm (pos. 6), which divides the internal volume of the tank into two chambers. It is made from a material with high elasticity and extremely low diffusion rate. Previously, rubber was more often used for these purposes, but such membranes still did not differ in durability. Modern devices usually use ethylene-propylene or butyl.
So, the membrane divides the tank into a water chamber (pos. 4) located on the side of the branch pipe, and into an air chamber (pos. 5) from the side of the nipple. And the volume of these chambers is a variable quantity.
- As already mentioned, an overpressure is preliminarily created in the air chamber (usually in the range from 1 to 1.5 atmospheres). Under its influence, the membrane falls down, and the water chamber has a minimum volume before filling the system.
- The system is filled with coolant and started up. In this case, a certain operating pressure is created in the circuit (optimal for this system). At the same time, the membrane bends somewhat - the volume of the water chamber has increased.
- As it heats up, the coolant increases in volume. The only place in the system where this "surplus" can fit is the water chamber of the tank. This means that its volume increases even more, and in the air chamber, which has significantly decreased because of this, the gas pressure increases.
- The coolant cools down, decreasing in the total volume - the gas pressure pushes the membrane down. That is, the necessary balance is achieved at any time, the optimal pressure value is maintained in the system.
- Well, if something went wrong, and the coolant has nowhere to expand (for example, the thermostatic automation of the system failed), then the safety valve of the "safety group" will work, bleeding off excess fluid and restoring balance - until the cause is identified and eliminated.
By the way, in some models of expansion tanks, the presence of a safety valve is provided in their very design.
The membrane can also have other shapes. So, balloon-type tanks are widely used. The features of their device are shown in the diagram below.
In such tanks, the membrane is made in the form of an elastic balloon (item 1), the edges of which are hermetically fixed in a flange with an inlet pipe (item 2). In fact, this balloon becomes the water chamber of the tank. And the rest of the space is an air chamber (pos. 3) with a preset pressure in it. When the coolant expands, the walls of the cylinder stretch, it acquires a pear-shaped shape (fragment on the right). The volume of the air chamber decreases, the pressure in it increases - and then everything, as in already described above example.
By the way, such tanks are quite popular because it is not difficult to replace a membrane that has come out of a standing position in them - thanks to its flange fastening. Diaphragm tanks very often simply cannot be repaired.
How much volume should an expansion vessel have in a closed heating system?
On sale there are lines of models of expansion tanks with a wide variety of volumes. Which one to choose for his systems? To determine this parameter, it is best to make a small calculation.
The formula for the calculations is as follows:
Vb =Vs ×k / D
We decipher the designations:
Vb- the required volume of the tank (minimum).
Vwith- the total volume of the heating system. How it can be determined has already been discussed above.
k- coefficient of thermal expansion of the coolant.
Here is a little more detail. The fact is that if antifreeze is used instead of water, then the expansion rates can be completely different, and depend on both the temperature and the concentration of glycol additives.
The table below will help you find the right value:
| Heating agent heating temperature, ° С | Glycol content,% | |||||||
|---|---|---|---|---|---|---|---|---|
| 0% (water) | 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 |
D- coefficient of efficiency of the expansion tank. It, in turn, is determined by the following formula:
D = (Qm – Qb) / (Qm + 1)
The following values are covered under the letter designations:
Qm- the upper threshold of the permissible pressure in the heating system. That is, this is exactly the indicator under which the actuation force of the safety valve in the "safety group" is adjusted.
Qb- pre-created pressure in the air chamber of the expansion tank. If the tank already has such a pumping, then this value will be indicated in the passport. But often the pressure is set independently using a conventional automobile pump and with control by the same automobile pressure gauge. The value has already been mentioned - as a rule, in the range from 1.0 to 1.5 atmospheres.
In order not to force the reader to carry out calculations manually, below is a convenient calculator that will perform the calculation in literally seconds.