What is the purpose of an expansion tank

It’s essential to comprehend the different parts of your heating system if you want to keep your house efficient and comfortable. The expansion tank is one such part that is essential to many heating systems. The expansion tank is a vital component that keeps your heating system running smoothly, despite its diminutive size.

Consider your home’s heating system as a closed loop that circulates steam or hot water to keep everyone warm. The expansion of the hot water or steam within the system results in a rise in pressure. Without a means to handle this expansion, the pressure might rise to dangerous levels and harm valves, pipes, and other parts.

The expansion tank is useful in this situation. The expansion tank essentially serves as a buffer, giving the increased volume of steam or water a safe place to expand without raising the pressure. It is comprised of a diaphragm, or flexible membrane, dividing a sealed chamber into two sections.

The air in the other half of the tank is compressed as a result of the expanding water or steam pushing against the diaphragm. By absorbing the extra pressure, this compression keeps it from building up inside the heating system. The compressed air in the tank pushes back when the system cools and the pressure drops, keeping the system’s pressure level steady.

Without an expansion tank, pressure changes brought on by the heating fluid’s expansion and contraction could cause a number of problems, such as leaks, harm to the boiler’s internal parts, and even system failure. The expansion tank ensures the safe and effective operation of your heating system and helps to extend its lifespan by offering a way to control pressure.

How to choose an expansion tank for a heating system

Every heating system has a number of components that are necessary for it to operate normally. An expansion tank is one of these components; this article will explain its function and mechanism. Additionally, we’ll talk about how to choose an expansion tank for heating a private residence.

What an expansion tank is for?

Everyone is aware, even from physics class in school, that heat causes any body to expand, and that the volume of liquids and gases increases. Since there is nowhere for a heated liquid to expand, it cannot expand like a gas can, and heating it in a closed vessel—the boiler’s tank—will cause the pressure inside to rise. The result could be a rupture in the tank’s walls.

Consider a coolant that has been heated in pipes from 20 to 80 degrees Celsius. When the liquid medium heats up, the pressure in the network will rise significantly if an expansion tank is not installed in the heating system, which could lead to the water bursting at the weakest point. Having a safety relief valve is a good idea. There is nowhere else for the extra water to go, so it will escape through it. The heating medium will just explode at one of the connections if there isn’t a valve.

The expanding volume of the coolant during heating requires an expansion tank. During the cooling process, it is reintroduced into the system simultaneously.

When the safety valve releases water, it cannot be refilled after cooling down and releases air into the empty space. This will cause an air lock to form, which will prevent the system from operating normally.

Types of expansion tanks

Calculations are used to determine the external shape and size variation of expansion tanks used for heating. Typically, there is just one pipe connecting the tank to the heating system. But different kinds of tanks serve different purposes and have distinct designs. Understanding these distinctions is essential to selecting the appropriate tank, so first we’ll list the varieties that are currently available:

• open type;
• closed, equipped with a membrane.

Note: Although closed expansion vessels without a diaphragm are still available, using them is strongly discouraged. We explain why below.

Open type tanks

These tanks, which are made of metal and have an open top of any shape, are utilized for open heating systems (or, alternatively, gravity, gravity). The coolant to the tank is supplied from below via a welded spigot on the upper portion of the side wall for attaching a hose or overflow pipe. The element is typically mounted in the house attic, above the entire system on the supply pipe.

Technically speaking, an open system is one from which water is taken out directly for domestic hot water requirements. It is only utilized in centralized networks, not in individual homes. Falsely, an open system is said to have natural coolant circulation.

Any heating expansion tank of the open type serves two purposes:

• serves to compensate for the expansion of the coolant;
• produces the removal of air from the system, since its top communicates with the atmosphere.

Its advantage is this, but it’s not the only one. An open tank can function well and long-lastingly in forced circulation systems as well because of its straightforward construction, which means there is nothing to break. But it also has a lot of drawbacks:

• The tank, installed in the attic, requires good insulation;
• During the season it is necessary to constantly monitor the water level in the tank and replenish it in time;
• the coolant is constantly saturated with oxygen from the atmosphere, which makes the metal parts of the boiler corrode faster;
• additional material consumption and installation difficulties.

Closed diaphragm tank

A more contemporary type of closed expansion tank is a cylindrical vessel with an internal rubber diaphragm. They are installed in the furnace room and used in schemes that involve forced coolant circulation. Additionally, the coolant supply is handled from the bottom, and the unit’s top is equipped with a service spool for air injection.

There are two types of rubber diaphragms used in the closed expansion tank of the heating system, which are commonly referred to as "pears":

• in the form of a diaphragm;
• balloon type.

Note: Some manufacturers’ tanks come with a detachable "pear" that can be replaced if it cracks.

Although a little bit more water can fit in the second type of tank, the membrane’s shape has no particular effect on how the device works. The "pear" that pumps air (or occasionally nitrogen) under a specific pressure needs to be adjusted for every system separately. Every closed expansion tank works in the same straightforward manner: as the coolant heats up, the network’s pressure rises, stretching the membrane and causing water to shoot into the tank. Everything operates in reverse order when it cools.

Due to its small size, the hermetic expansion tank for a wall-mounted gas boiler is frequently built inside the heat generator. Furthermore, there is no communication between the device and the atmosphere, and there is no diffusion of oxygen into the coolant. One of the weak points of these tanks is the membrane, which rarely lasts up to ten years and can’t always be replaced.

A third kind of compensating device is a vacuum expansion tank used for closed-type heating that does not have a "pear." They are hard to come by and are useless because this kind of design is the least successful. This is unacceptable because the air actively diffuses into the water because it acts as the membrane in the container. Then, since the tank’s level will always rise, there won’t be anywhere to make up for the expansion.

Recommendations for selection

If the house is designed or built with a natural circulation system, the open-type expansion tank is specifically for you. It is not worth it to use a vacuum tank here, wise, as the water in this system moves only because of the specific gravity difference, and the device might not function as intended. It doesn’t matter if you make or purchase an open vessel—the most important thing is to accurately determine the expansion tank’s volume, which we will discuss below.

Vacuum membrane vessels present a slightly more intricate scenario. One word of caution: once in the store, keep in mind that the tank for heating is not the same as a hydroaccumulator for water supply, despite the numerous similar products. They are so similar on the outside—they might even share the same color—that choosing a tank for this feature is not an option. The nameplate inscription, which indicates that the tanks can be heated to an operating temperature of up to 120 oC and pressure up to 3 bar, helps to identify the tanks. up to 70 oC and 10 bar of pressure, respectively, on the hydroaccumulator.

When making a decision, it’s important to consider the option of switching out the "pear" in the event that it breaks. The closed-type tank’s calculation results are used to determine the apparatus’s size.

Calculation of the expansion tank

Numerous methods exist in technical literature and the vast Internet that can be used to calculate the expansion tank for a heating system that uses both forced and natural coolant circulation. However, the majority of them have numerous intricate formulas pertaining to boiler capacity and other variables. If you calculate the tank’s volume using a less complicated method, you won’t make a mistake.

The technique is predicated on the claim that the system’s total water volume at maximum heating will rise by no more than 5%. That is, determine the water volume first using the formula below:

• the amount of coolant in the boiler tank – according to the passport;
• volume of water in the pipes – using the formula for the area of the circle find the cross-sectional area of each pipe and multiply it by the length;
• capacity of radiators – also according to the passport on the product.

After a summary of the findings, you decide on and compute the expansion tank with a reserve, deducting 10% of the total instead of 5. Its capacity will be this.

Conclusion

The only difficult part of choosing a closed-type tank is ensuring that it is installed correctly after calculating the volume. You can also do this on your own by following the directions that come with the product.

In an article about the purpose of an expansion tank for a website focusing on heating and insulation of houses, the main thesis could be: "The expansion tank is a crucial component of a home heating system, designed to manage the fluctuations in water volume that occur as the water heats up and cools down. Its primary purpose is to ensure the safety and efficiency of the system by providing a space for the expanding water to go without causing pressure buildup, potential damage to the system, or water wastage. By allowing for the expansion of heated water, the expansion tank helps maintain stable pressure levels within the heating system, prolonging its lifespan and preventing costly repairs. Understanding the role of the expansion tank is essential for homeowners looking to maintain a well-functioning and efficient heating system in their homes."

Expansion tank for heating systems

A private home’s heating system is a vital life support system, so it must operate steadily. Pressure is one of the variables that needs to be watched. A boiler that is set too low won’t operate, and one that is set too high will cause the machinery to break down too soon. For heating purposes, you need an expansion tank in order to maintain system pressure. The gadget is simple, but without it, the heating won’t function for very long.

Why do you need an expansion tank for heating

Heater coolant frequently experiences temperature fluctuations as the heating system runs. It is obvious that the liquid’s volume changes in this situation. It rises and falls. Simply said, extra coolant is diverted into the expansion tank. Therefore, this device’s function is to adjust for variations in fluid volume.

The heating expansion tank’s working principle

Types and device

Water heating is available in two varieties: open and closed. A circulation pump provides the coolant circulation in a closed system. It merely forces water through the pipes at a set speed; it doesn’t produce any more pressure. Such a heating system has a closed-type expansion tank for heating. The reason it is called closed is that it is a sealed container with an elastic membrane dividing it into two sections. Air is present in one section, and extra coolant is forced out of the other. The tank is also known as a membrane tank due to the membrane’s presence.

A circulation pump is not necessary for an open heating system. Here, any container—even a bucket—to which the heating pipes are connected serves as the expansion tank for the heating system. Although it can be, a lid is not even necessary.

In its most basic form, it is a metal container that is welded together and placed in the attic. There is a big drawback to this choice. Because of the leak in the tank, coolant evaporates and needs to be constantly monitored in order to be refilled. Manually operating from a bucket is an option. This is not very practical because there’s a chance you won’t remember to replenish the water. This raises the possibility of system inflation, which could result in the system failing.

More practical automated water level control. It is true that in the event that the tank is overfilled, the overflow hose (pipe) and water supply must be pulled out of the attic along with the heating pipes. However, there’s no need to check the coolant level on a regular basis.

Volume calculation

The volume of the expansion tank for heating can be found using the following very easy method: 10% of the system’s coolant volume is computed. It was something you ought to have calculated when creating the project. In the event that these data are unavailable, you can estimate the volume by pouring in fresh coolant while simultaneously measuring the old one (letting it pass through the meter). Doing the math is the second method. Calculate the system’s pipe volume and then add the radiator volume. This represents the heating system’s volume. This number yields a result of 10%.

The form may vary.

Using the formula to calculate the expansion tank’s volume for heating is the second method of doing so. Here, the system’s volume (represented by the letter C) will also be necessary, but additional information will also be needed:

• the maximum pressure Pmax at which the system can operate (usually the maximum pressure of the boiler);
• initial pressure Rmin – from which the system starts to work (this is the pressure in the expansion tank, it is indicated in the passport);
• coefficient of expansion of the coolant E (for water 0,04 or 0,05, for antifreeze is indicated on the label, but usually within the range of 0,1-0,13);

Using all of these numbers, use the following formula to determine the precise expansion tank volume for the heating system:

Formula for figuring out how big the heating expansion tank should be

Even though the calculations are simple, are they still worthwhile to make the effort? The answer is clear-cut: no—if the system is of the open type. The vessel’s cost is not significantly affected by its volume, and it can be manufactured on its own.

Calculations should be made for closed-type expansion tanks used for heating. The volume has a significant impact on their price. However, in this instance, it is still preferable to take it slowly because a low volume causes the system to break down quickly.

Install a second expansion tank if the boiler already has one and its capacity is insufficient for your system. All in all, they ought to provide the necessary volume (installation is not an exception).

What will result from an insufficient expansion tank volume

The coolant expands during heating, and any excess is stored in the expansion tank. If the excess is not completely disposed of, the emergency pressure relief valve drains it. In other words, the sewage system receives the coolant.

Fundamentals of how a graphic representation works

Then, when the temperature decreases, the volume of the coolant decreases. But since there"s less coolant 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 little, the boiler may not work. This equipment has a lower pressure limit at which it is operable. When the lower limit is reached, the equipment is blocked. If you are at home at the time, you can remedy the situation by adding coolant to the system. If you"re not there, the system can defrost. By the way, working at the limit also does not lead to anything good – the equipment quickly fails. Therefore, it is better to be a little over-insured and take a slightly larger volume.

Cistern pressure

Certain boilers (mostly gas boilers) have a passport that specifies the expander’s recommended pressure. In the event that no such record exists, the system’s working pressure should be 0.2–0.3 atm lower in the tank for optimal operation.

A low-rise private home’s heating system typically operates between 1,5 and 1,8 atm. Thus, the tank’s pressure should be between 1.2 and 1.6 atm. An everyday manometer is used to measure the pressure. It is attached to the nipple, which is situated in the upper portion of the tank. You can access the spool by unscrewing the plastic cover that conceals the nipple. Through it, excessive pressure can also be released. The way it works is similar to a car spool valve in that you bend the plate with a thin object and release the air to the necessary pressures.

The pumping nipple is located where?

The expansion tank’s pressure can also be raised. You will need an automotive pump with a manometer for this. After attaching it to the nipple, you raise the pressure to the required levels.

The tank is disconnected from the system for each of the aforementioned procedures to be completed. It is not required to remove it if it is already installed. On-site, you can check the pressure in the heating system’s expansion tank. Just exercise caution! When the system is not operating and the heating medium has been removed from the boiler, check and adjust the expansion tank’s pressure for heating. It is crucial that the boiler’s pressure be at zero in order to accurately measure and adjust the tank. Consequently, the water is completely drained. Next, we use a manometer to connect to the pump and adjust the parameters.

Where to put it in the system

In a closed system, the expansion tank is positioned to create an opposing flow after the boiler but before the pump. This increases the system’s dependability. Therefore, the precise installation location is determined by the location of the circulation pump.

Installation plan for the heating expansion tank

It has a tee connecting it to the system. The perpendicular outlet is directed upwards, a tee is cut into the pipe, and the tank is screwed onto it. The tank is turned upward, but you will need to make an elbow if the wall prevents you from placing it. The expansion tank can now be regarded as installed.

An example of a faucet installation

However, it is preferable to add another tee after the tank, on the free outlet of which to install a stopcock, for convenience of checking. This cuts off the membrane tank, allowing for inspection without completely emptying the system. After turning off the faucet, empty the boiler’s water supply. Verify the pressure in the boiler’s disconnected branch. It ought to be zero. when you’re able to finish all remaining adjustments.

Expansion tank for heating – a necessity

Any property owner who wishes to efficiently manage the maintenance of their home’s heating system must select the appropriate equipment and ensure a high-quality installation in compliance with established guidelines. You can only anticipate that the house will be comfortable during the heating season if these requirements are satisfied (see also "The rules of preparation for the heating season of the residential building").

Why do you need an expansion tank

Since the coolant in the heating circuit and pipeline has a fixed mass and the elasticity in the pipeline tends to zero, a change in the liquid’s temperature will inevitably alter the system’s pressure. The truth is that heating causes any form of heat carrier, including water, to expand thermally, which results in an increase in volume. Large problems cannot be avoided if the load is greater than the radiator’s or the pipeline’s bursting strength.

The reason for a possible accident is that water, which is incompressible, changes volume when heated and still remains in an almost unchanged state. Hence, the likelihood that a water hammer can occur increases dramatically because there are no elastic interactions in a liquid medium.
The solution to this problem is to connect a tank with an easily compressible substance, more precisely with air. When there is an expansion tank for heating, such as the one in the photo, when the volume of the liquid increases, the pressure increases slightly.
To ensure that the oxygen in the air chamber of the device, dissolving in water, does not cause corrosion of some elements of the system (closed type) it is separated from the liquid with a rubber membrane.

There is an expansion tank in addition to each household’s closed heating scheme:

• in open-type heating structures where there is contact with atmospheric air;
• in centralized heating systems with overhead spillage. In this case, the expansion tank for heating is installed in the attic and connected to a part of the pipeline of the heating structure of the building, supplying the heat carrier.

To remove air locks from the heating system, these devices must be installed in both versions. The distance between two central heating strings is roughly two meters, and even less in private homes where the heat carrier circulates naturally. The liquid pressure is in no way able to remove the air from the upper portion of the heating structure at such differences. Thus, the solution is to install a tank that gathers air where it accumulates and vents it out when the system starts up. Every air plug in the radiators and pipes is driven upward and into the expansion tank.

Nothing needs to be done if an open system is being used. When the owner needs to open the air tap, the air will instantly connect to the atmosphere, in contrast to the closed version (see also: "Open and closed heating system – advantages and disadvantages in comparison ").

Expansion Tank Purpose	Explanation
Pressure Regulation	Controls pressure variations caused by thermal expansion in the heating system.
Prevention of Damage	Protects pipes and other components from potential damage due to excessive pressure buildup.

Although an expansion tank is a small, unseen component of your heating system, it plays a vital role in preserving both safety and efficiency. Its main function is to regulate the variations in water volume that arise during the operation of your heating system.

Water expands when it gets hotter. Pressure within your heating system may build up if there is nowhere for this expanded water to go, which could cause damage or even failure. This is where the expansion tank comes into play, giving the expanded water a specific area to go into that releases pressure and safeguards your system.

An expansion tank’s ability to protect your heating system from the damaging effects of excessive pressure is one of its main advantages. The expansion tank helps stop leaks, bursts, and other types of damage that can happen from pressure buildup by allowing water to expand without creating a pressure spike.

Additionally, an expansion tank improves your heating system’s overall efficiency. It guarantees that your system runs smoothly and consistently, free from the interruptions and inefficiencies that can result from pressure fluctuations, by maintaining ideal pressure levels.

In conclusion, even though an expansion tank might appear to be a minor part of your heating system overall, it plays an essential role. It contributes to the preservation of system integrity, safety, and efficiency by controlling water expansion and releasing pressure, ultimately extending the life of your heating system and guaranteeing dependable operation.

Video on the topic

Why do you need an expansion tank (hydrophore, hydro accumulator)?

Why you need an expansion tank in the heating system?

How the expansion tank for the heating system works