How the diaphragm type expansion tank works

It’s critical to comprehend the parts of your system when it comes to your home’s insulation and heating. The expansion tank of the diaphragm type is one important component. This essential part keeps your heating system operating efficiently and lasting a long time. We will examine the operation of the diaphragm type expansion tank and its importance in the heating system of your house in this post.

Water is heated in a typical heating system and expands as a result. If there is nowhere for this expanded water to go, pressure inside the system may build up and possibly cause damage. This is where expansion tanks of the diaphragm kind are useful. It is made to hold this expanded water, guaranteeing the safe and efficient operation of your heating system.

So, how does an expansion tank of the diaphragm type operate? It’s a clever mechanism that is comparatively simple. The air side and the water side of the tank are divided by a rubber diaphragm. The air on the other side of the diaphragm is compressed as the expanding water in the heating system enters the expansion tank. The expansion tank can absorb the extra water volume thanks to this compression without the system’s pressure rising noticeably.

Consider the diaphragm type expansion tank as an automobile’s shock absorber. The shock absorber compresses when you hit a bump, absorbing the impact and shielding the vehicle from harm. Comparably, the expansion tank in your heating system absorbs the extra volume created by the expanding water, preventing pressure from building up and possibly damaging the system.

The efficiency of the diaphragm type expansion tank is one of its main benefits. In contrast to previous iterations that employed a piston or a floating ball, the diaphragm type exhibits greater dependability and lower failure rates. It also needs little upkeep, which makes it a great option for homeowners searching for a hassle-free way to keep their heating system maintained.

Aspect	Description
Function	The diaphragm type expansion tank works by allowing the water in a heating system to expand when it"s heated. It consists of two separate chambers divided by a flexible diaphragm. One chamber is for water, and the other for air. As water heats up, it expands, pushing against the diaphragm, compressing the air in the other chamber.
Role of Diaphragm	The diaphragm, usually made of rubber or similar material, is flexible. As the water expands, it pushes against this diaphragm, compressing the air on the other side. This design prevents water from coming into contact with the air, which eliminates the risk of corrosion.

In the realm of heating and insulating your house, understanding how the diaphragm type expansion tank works is essential. This tank is a crucial component of your heating system. Essentially, it operates by accommodating the expansion of water when it"s heated. The diaphragm inside the tank separates the water from the air, maintaining two distinct chambers. As the water heats up, it expands, pushing against the diaphragm, which then compresses the air in the tank. This process allows for the expansion of water without causing pressure fluctuations in the heating system. In simpler terms, the tank acts as a shock absorber, preventing your heating system from becoming damaged due to pressure changes caused by the heated water. Understanding the functioning of the diaphragm type expansion tank is key to maintaining an efficient and safe heating system for your home.

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

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

What is the purpose of the expansion tank in the heating system??

Because the volume of the heat-carrying fluid increases in temperature when the coolant is heated, this causes a significant increase in pressure in both the boiler and the heating system circuit. This physical phenomenon has the potential to destroy the boiler or pipelines because the liquid is essentially an incompressible medium and the heating system is hermetically sealed. If there weren’t one significant factor, the issue could be resolved by installing a straightforward valve that can release the excess hot water volume into the outside environment.

Air will replace the released coolant in the heating circuit when the liquid compresses during cooling. Any heating system’s worst enemy are air plugs, which make network circulation impossible. For this reason, the heating radiators need to have their air bled out. Heating cold water is far more expensive than heating the heat-carrying liquid that was brought to the boiler via the return pipeline, and replacing the coolant in the system on a regular basis is also very expensive.

Installing an "expansion tank," or tank connected to the system via a single pipe, solves this issue. The heating expansion tank’s volume balances out the excess pressure inside, enabling steady circuit operation. The form and dimensions of the heating system’s expansion tanks vary depending on the kind of heating circuit and the computation’s outcomes. These days, tanks come in a variety of shapes, from traditional cylindrical tanks to so-called "pills."

Types of heating systems

Building heating networks come in two varieties: open and closed. In centralized heating networks, open (self-pumping) heating systems are utilized to enable direct water intake for hot water supply requirements, something that is not feasible in individual homes. This kind of device is found at the circuit’s upper point for the heating system. The heating expansion tank serves the purpose of naturally removing air from the system in addition to equalizing pressure drops because it can communicate with the external atmosphere.

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

A closed-type heating expansion tank with an integrated internal membrane is used with a more contemporary closed scheme.

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

Device and principle of operation

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

There are several types of diaphragms:

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

The instructions that come with items like expansion tanks for closed-type heating explain how to adjust the gas pressure in each system in a unique sequence. Some manufacturers include the option to replace the diaphragm in the design of their expansion tanks. This method slightly raises the device’s initial cost, but in the event that the membrane is harmed or destroyed later on, replacing it will be less expensive than buying a new expansion tank.

Practically speaking, the shape of the membrane has no bearing on how effective the devices are; the only thing to be aware of is that the closed-type cylinder expansion tank for heating has a marginally bigger capacity for heat-carrying fluid.

Their working principle is also the same: the diaphragm stretches, compressing the gas on the other side and allowing extra coolant to enter the tank when water pressure in the network rises as a result of expansion during heating. The procedure is reversed in the event of cooling down and a corresponding drop in network pressure. As a result, the network’s continuous pressure is controlled automatically.

It is important to note that it will be extremely challenging to achieve the stability of the heating network if you purchase a heating expansion tank at random without performing the required computations. The system won’t produce the necessary pressure if the tank is significantly larger than it needs to be. An emergency could arise if the tank is smaller than necessary because it won’t be able to hold the large amount of liquid that is carrying heat.

Calculation of expansion tanks

In order to determine the expansion tank for closed-type heating, one must first determine the overall system volume, which includes the volume of the heating boiler, heating devices, and circuit pipelines. Boiler and radiator volumes are listed on their passports, and pipeline volumes are calculated by multiplying the internal cross-sectional area of the pipes by the length of the pipe. If the system contains pipelines with varying diameters, each pipeline’s volume must be calculated independently before being added together.

Additional calculations are made using the formula V = (Vs x k) / D for devices like expansion tanks for closed-type heating, where:

In any event, it is important to keep in mind that the heating expansion tanks must guarantee a 10% increase in the network’s heating medium volume; that is, if the system’s heat-carrying liquid has a 500 l volume, the combined volume of the tank and the system should be 550 liters. As a result, you require a heating system expansion tank that holds at least 50 liters. This method of estimating the volume is highly imprecise and could lead to a needless expenditure for the acquisition of a larger expansion tank.

At the moment, expansion tank calculations can be done online using calculators. When choosing equipment through such services, it is essential to perform calculations on three different websites in order to assess how accurate the Internet calculator’s calculation algorithm is.

Manufacturers and prices

The only issues with purchasing an expansion tank for heating right now are with the type and volume of the device, as well as the buyer’s financial situation. There are many different device models available on the market from both domestic and foreign manufacturers. It should be mentioned, though, that it is preferable to pass on a purchase of a closed-type expansion tank for heating if the cost is significantly less than that of the major rivals.

Low cost is a sign of the manufacturer’s unreliability and the poor quality of the materials used in its production. This is often the case with Chinese production. Like with other products, there won’t be much of a price difference for a high-quality heating expansion tank—roughly two to three times. Since ethical manufacturers use nearly identical materials, the location of production and the sellers’ pricing policies are the only factors contributing to the 10-15% price difference between similar models.

In this particular market segment, domestic manufacturers have demonstrated success. They are able to produce goods at a lower cost while maintaining a level of quality comparable to the best global brands thanks to the installation of contemporary technological lines in their production.

It is important to remember that purchasing an expansion tank for closed-type heating is just one aspect of the equation; another is proper installation.

If you have the required abilities and follow the directions, you can install it on your own. To ensure a stable heating network and rule out any malfunctions, it is best to contact professionals if the master is still unsure about his level of expertise.

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Expansion membrane tank for heating: design features and principle of operation

Diaphragm expansion tank for Reflex NG 140.

An component of a closed heating system called an expansion membrane tank works to maintain the necessary pressure while accounting for the coolant’s thermal expansion.

Be aware that membrane tanks are utilized in water supply systems in addition to heating systems. They both keep the system pressure steady and "mitigate" hydrostrokes that happen when pumping stations are turned on and off.

Membrane tank design

The heating expansion diaphragm tank is a cylindrical steel body that is hermetically sealed and coated in red epoxy lacquer (blue lacquer tanks are made for cold water). The housing is divided into two chambers, one for gas and the other for water. The diaphragm, which is made of butyl rubber, is movable and gas-tight. The diaphragm can operate steadily at a range of temperatures (-10 to +100°C) and for up to 100,000 cycles because of this material.

The diaphragm expansion tank’s design.

The interaction of the coolant and gas is virtually eliminated by the membrane. The longer the pre-pressure in the gas chamber is maintained, the longer the tank’s service life. This is made possible by the lack of such interaction.

Be aware that modern, high-quality diaphragms "stick" to the tank walls rather than just pulling out when the coolant expands. This principle of operation extends the diaphragm’s service life.

The identical pressure in both chambers enables the heating system’s portion to remain tightly sealed. The mixture that contains nitrogen is poured into the air chamber. The nitrogen is compressed by the coolant’s expansion, enabling the coolant to "enter" the water chamber.

The majority of contemporary diaphragm heating tanks feature an integrated nipple, akin to that of a standard car, that can be utilized to "pump up" the air chamber and raise its internal pressure. With a pump or compressor, you can accomplish this on your own at home. But it’s important to keep in mind that nitrogen, not air, needs to be pumped in. The device’s service life will unavoidably be shortened because the oxygen in the air will accelerate the corrosion of the tank body’s walls. However, nitrogen is neutral and doesn’t encourage corrosion.

Wall mounting of the safety group and tank.

Fastening of the expansion tank clamp.

Installation is made easier by the external threaded connection on the tank body’s outlet. The threads can vary based on the model and include:

• In low pressure tanks (from 0.5 to 1.5 bar) – 3/4″ or 1″;
• Medium pressure tanks (1.5 bar) have 1″;
• For high-pressure tanks (3 bar and above) – 1″ to flange connection DN 100;

Operating principle of the diaphragm tank

The coolant warms up and expands when the heating system is turned on. The expansion tank’s water chamber receives this extra volume. The coolant from the water chamber is forced back into the heating circuit when the coolant cools down because of the pressure in the air chamber pushing the diaphragm out.

Furthermore, as previously indicated, the diaphragm tank keeps the necessary pressure throughout the heating system. For instance, if there is a tiny coolant leak somewhere, the pressure in the entire system should decrease, but this does not occur because the diaphragm is pushed back into the system by the air chamber’s pressure, which results in a limited make-up.

Diaphragm tank equipped with a safety group.

Inadequate operation may cause damage to the membrane:

• There is a probability of rupture of the membrane in case when filling the water chamber with coolant, the necessary pressure was not created in the air chamber;
• Before draining gas from the air chamber, it is necessary to shut off and drain the coolant from the water chamber.

Calculation of the tank

The thermal fluid’s volume increases by 0.3-0.4% on average with each degree Celsius of heating. The needed tank volume is computed using these data.

The percentage of coolant (water) expansion that varies with heating temperature:

The coolant temperature (°Ρ)

Crucial! A ball valve with a drain that allows the coolant flow to be stopped is a feature of all heating diaphragm tanks. This is required in order to replace the tank quickly and conveniently in the event that it fails.

Open type expansion tank

Currently, this kind of expansion tank is hardly utilized, as it has the following drawbacks:

Expansion tank open.

1. The heat carrier is in constant contact with air, which leads to the system blowing out and the appearance of air plugs. Therefore, it is necessary to remove air regularly or an air separator must be installed. Otherwise, air can lead to corrosion of individual elements of the heating system, as well as to a decrease in the heat output of heating devices;
2. Because the heat transfer medium is constantly in contact with air, it vaporizes. It is necessary to regularly add coolant to the system;
3. Air microbubbles circulating through the heating system create unpleasant noises in pipes and radiators, and also lead to premature wear of the circulation pump parts (blades and bearings). In addition, microbubbles "reduce the characteristics" of the circulation pump;
4. Unlike the membrane tank, which can be installed at any point of the system (near the boiler, in the basement,…), the open-type expansion tank is installed only at the highest point. This leads to an increase in the cost of the system, t.к. it is necessary to use additional pipes and fittings for mounting the tank at the top point.

Related notes:

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All about the expansion tank for water supply: principle of operation, types, self-installation

The device and functions of this equipment

The purpose of the expansion tank is to keep the water supply system’s pressure constant. Equipment of the closed membrane type is most frequently used for water supply. It’s a container with an installed rubber diaphragm. It creates a division between the air and water chambers within the unit. The latter is filled with water by the electric pump after the system has been turned on. The air chamber’s volume is diminished. The pressure rises as the tank’s air volume decreases.

The water supply system’s expansion tank is made of membrane material. Two chambers, one for air and the other for water, are separated by a rubber diaphragm.

When it surpasses the predetermined threshold, the pump will turn off on its own. It won’t activate until the water begins to flow from the tank’s water chamber and the pressure falls below the lowest programmed pressure. The cycle of "switch-off and switch-on" is automatically repeated. A pressure gauge that can be mounted on the apparatus can be used to measure the pressure within the system. You can personalize the unit by choosing your desired operating pressure range.

When installed in a water supply system, a diaphragm expansion tank serves multiple purposes simultaneously.

• Maintains pressure when the pump is switched off.
• It protects the system from a possible hydraulic shock caused by voltage fluctuations in the mains or air in the pipelines.
• Keeps a certain amount of water pressurized.
• Protects pumping equipment from premature wear and tear.

When using an expansion tank, it is possible to meet the water demand using the liquid that is stored in the tank rather than turning on the pump when water consumption is low.

Types of diaphragm tanks

Equipment for expansion membranes comes in two primary varieties.

Device with replaceable membrane

The ability to swap out the diaphragm is the primary differentiator. It is taken out using a unique flange that is secured with multiple bolts. It should be noted that in large-volume devices, the diaphragm is additionally fixed to the nipple by its rear portion in order to stabilize it. The device’s ability to keep the water filling the tank inside the diaphragm and away from the interior of the tank is another feature. This greatly increases the equipment’s lifespan by preventing corrosion on metal surfaces and potentially contaminating the water itself. There are versions of these models that are vertical and horizontal.

Because the most delicate component of the system can be changed and the water does not come into contact with the device’s metal body, devices featuring replaceable membranes have longer service lives.

Device with a stationary diaphragm

In these devices, a diaphragm that is fixed in place divides the inner portion of the tank into two sections. If the diaphragm fails, the apparatus will need to be replaced because it is not replaceable. The device has two parts: one has air and the other has water. Because the water is in direct contact with the device’s internal metal surface, it may corrode more quickly. The interior surface of the water-filled portion of the tank is painted with a unique substance to stop metal deterioration and water contamination. But this kind of defense isn’t always reliable. There are two varieties of the devices: horizontal and vertical.

Various devices with a diaphragm that is fixed rigidly. The equipment’s walls are assumed to be in contact with the water in the design.

How to choose the right device?

The primary feature that guides the selection of equipment is its volume. The following elements need to be considered:

• The number of people using the water supply system.
• The number of water intake points, which include not only showers and faucets, but also household appliances, such as washing machines and dishwashers.
• The probability that the water will be used by several consumers at the same time.
• Limit number of start-stop cycles per hour for the installed pumping equipment.

When selecting an expansion tank, experts advise referring to these indicators:

• If the number of consumers does not exceed three people, and the installed pump has a capacity of up to 2 cubic meters. If the pumping capacity is between 20 and 24 liters per hour, a tank volume of 20 to 24 liters is selected.
• If the number of consumers from four to eight people and the pump capacity is within 3.5 cubic meters, the main characteristic based on which to choose a pump is its capacity. m per hour, a tank volume of 50 liters is installed.
• If the number of consumers more than ten people and the pumping capacity of the pumping equipment is 5 cubic meters per hour, choose an expansion tank with a capacity of 50 liters per hour. m per hour, choose an expansion tank for 100 liters.

When selecting the right model of the device should take into account that the smaller the volume of the tank, the more often the pump will be turned on. And also the fact that the smaller the volume, the greater the probability of pressure surges in the system. In addition, the equipment is also a reservoir for storing a certain amount of water. The volume of the expansion tank is also adjusted on this basis. It should be known that the design of the device allows the installation of an additional tank. And this can be done in the course of operation of the main equipment without labor-intensive dismantling work. After installation of the new device, the volume of the tank will be determined by the total volume of the tanks installed in the system.

When selecting an expansion tank, special consideration should be given to its manufacturer in addition to its technical specifications. Seeking low prices can have far more serious consequences. The majority of the time, the least expensive materials are employed to create eye-catching models that, as experience has shown, aren’t always of excellent quality. The quality of the rubber used to make the membrane is particularly crucial. This has a direct impact on the longevity of the tank as well as the security of the water it produces.

When purchasing a tank with a replaceable membrane, the cost of the consumable element must be specified. Often, dishonest manufacturers greatly overcharge for the replacement membrane in an effort to maximize profits. It will be more appropriate in this situation to select a different company’s model. Large manufacturers are typically willing to take accountability for the caliber of their output because they place a high emphasis on their brand. Therefore, it makes sense to start by looking at these brands’ models. These are Reflex, Zilmet, Aquasystem (Germany) and Dzhileks and Elbi (Russia).

Depending on the needs of the users, the expansion tank volume for the water supply can vary. You can install an extra device if you eventually need a higher volume.

Anyone looking to improve the insulation and heating in their home must understand how a diaphragm-type expansion tank operates. For a hydronic heating system to remain effective and long-lasting, the expansion tank is essential. Despite being comparatively simple to operate, it has a big impact on the system’s overall performance.

The diaphragm-type expansion tank’s primary function is to allow for water expansion in closed-loop heating systems. Water expands when it gets hotter. This increased volume might cause a pressure buildup in the system without an expansion tank, which could result in damage. By absorbing the expanded water volume, the expansion tank serves as a buffer, preventing excessive pressure and preserving a safe, stable system pressure.

As the name implies, the diaphragm is one of the most important parts of a diaphragm-type expansion tank. The water and air chambers of the tank are divided by this pliable partition. The diaphragm flexes in response to an increase in water volume, compressing the air within the tank. The system can handle the increased water volume thanks to this air compression without experiencing a pressure spike. It’s a clever yet uncomplicated fix for a potentially dangerous problem.

The optimal functioning of an expansion tank of the diaphragm type is contingent upon proper installation and maintenance. It’s crucial to check that the tank is installed in the right spot and that its size is appropriate for the heating system during installation. Frequent upkeep will help guarantee that the expansion tank keeps working properly for the duration of its life. Examples of this maintenance include checking for leaks and making sure the tank has the right amount of air pressure.

To sum up, a hydronic heating system’s diaphragm-type expansion tank is an essential part. It contributes to the safety and efficiency of the system by permitting water to expand without creating pressure spikes. A thorough understanding of the operation and proper installation and maintenance will help to ensure your heating system operates at its best and lasts a long time.

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