What is the pressure in the expansion tank of the water supply system. Membrane tanks - types, principle of operation and rules of use
An autonomous water supply system today no longer surprises anyone. Such designs are very convenient and practical, however, their operation often requires devices that a person using only centralized water supply may simply not know about. For example, autonomous system water supply will work uninterruptedly for a long time only if it is turned on expansion tank for water supply. Modern industry produces many different models of such devices. To choose the best option for yourself, you need to navigate the types of equipment and have a good idea of the principle of its operation.
The device and functions of this equipment
The expansion tank is designed to maintain pressure in the water supply system. Most often, closed membrane-type equipment is used for water supply. It is a container inside which a rubber membrane is installed. It divides the device into two chambers: air and water. After starting the system, the electric pump fills the latter with water. As a result, the volume of the air chamber decreases. The smaller the volume of air in the tank, the higher the pressure.
As an expansion tank for the water supply system, a membrane-type design is used. The rubber diaphragm divides the device into two chambers: air and water
As soon as it exceeds the programmed mark, the pump will be automatically turned off. It will turn on only after the pressure drops below the minimum programmed mark, while water begins to flow from the water chamber of the tank. The cycle "off-on" is repeated automatically. The pressure in the system can be checked with a pressure gauge that can be installed on the equipment. The device can be configured by selecting the preferred operating pressure range.
The membrane expansion tank installed in the water supply system performs several functions at once:
- Maintains pressure when the pump is off.
- Protects the system from possible water hammer caused by power surges in the network or air entering the pipeline.
- Keeps some water under pressure.
- Protects pumping equipment from premature wear.
The use of an expansion tank makes it possible, with low water consumption, not to turn on the pump, but to cover the water needs due to the liquid stored in the tank.
Types of membrane tanks
There are two main types of expansion membrane equipment.
Membrane instrument
The main distinguishing feature is the possibility of replacing the membrane. It is removed through a special flange, which is held on by several bolts. At the same time, it should be taken into account that in large-volume devices, in order to stabilize the membrane, it is additionally fixed with the back part to the nipple. Another feature of the device is that the water filling the tank remains inside the membrane and does not come into contact with the inside of the tank. That protects metal surfaces from corrosion, and the water itself from possible contamination and significantly extends the life of the equipment. Models are available in both horizontal and vertical versions.
Devices with a replaceable membrane have a longer service life, since the most vulnerable element of the system can be replaced and water does not come into contact with the metal case of the device
Stationary Diaphragm Device
In such devices, the inside of the tank is divided into two parts by a rigidly fixed membrane. It cannot be replaced, therefore, if it fails, the equipment will have to be changed. One part of the device contains air, the other contains water, which is in direct contact with the inner metal surface of the device, which can provoke its rapid corrosion. To prevent metal destruction and water pollution, the inner surface of the water part of the tank is covered with a special paint. However, this protection is not always durable. Devices of horizontal and vertical types are issued.
A type of device with a rigidly fixed membrane. The design assumes that water is in contact with the walls of the equipment
How to choose the right device?
The main characteristic on the basis of which equipment is selected is its volume. In this case, the following factors must be taken into account:
- Number of people using the water supply system.
- The number of water points, which include not only showers and taps, but also household appliances, such as washing machines and dishwashers.
- The probability that water will be consumed by several consumers at the same time.
- The maximum number of start-stop cycles per hour for installed pumping equipment.
- If the number of consumers does not exceed three people, and the installed pump has a capacity of up to 2 cubic meters. m per hour, a tank with a volume of 20 to 24 liters is selected.
- If the number of consumers is from four to eight people and the pump capacity is within 3.5 cubic meters. m per hour, a tank with a volume of 50 liters is installed.
- If the number of consumers is more than ten people and the performance of pumping equipment is 5 cubic meters. m per hour, choose an expansion tank of 100 liters.
When choosing the right model of the device, it should be borne in mind that the smaller the volume of the tank, the more often the pump will turn on. As well as the fact that the smaller the volume, the greater the likelihood of pressure surges in the system. In addition, the equipment is also a reservoir for storing a certain supply of water. Based on this, the volume of the expansion tank is also adjusted. You should be aware that the design of the device allows the installation of an additional tank. Moreover, this can be done during the operation of the main equipment without labor-intensive dismantling. After installation of a new device, the volume of the tank will be determined by the total volume of the tanks installed in the system.
In addition to technical characteristics, when choosing an expansion tank, special attention should be paid to its manufacturer. The pursuit of cheapness can result in much more significant costs. Most often, the cheapest materials are used to produce models that attract with their cost, and, as practice shows, they are not always of high quality. The quality of the rubber from which the membrane is made is especially important. Not only the service life of the tank directly depends on this, but also the safety of the water that comes from it.
When buying a tank with a replaceable membrane, be sure to clarify the cost of the consumable item. Very often, in the pursuit of profit, not always conscientious manufacturers significantly overestimate the price of a replacement membrane. In this case, it would be more appropriate to choose a model from another company. Most often, a large manufacturer is ready to be responsible for the quality of its products, since it values its reputation. Thus, it is worth considering the models of just such brands in the first place. These are Dzhileks and Elbi (Russia) and Reflex, Zilmet, Aquasystem (Germany).
The volume of the expansion tank for water supply can be different, it is selected based on the needs of users. If a larger volume is subsequently required, an additional device can be installed
Features of self-installation
All expansion tanks can be divided into two groups, determined by the connection method. There are vertical and horizontal models. There are no particular differences between them. When choosing, they are guided by the parameters of the room where the equipment will be placed. During the installation process, the following recommendations should be followed:
- The expansion tank is installed in such a way that it can be easily accessed for maintenance.
- It is necessary to provide for the possible subsequent dismantling of the connecting pipeline for the replacement or repair of equipment.
- The diameter of the connected water supply can not be less than the diameter of the branch pipe.
- It is necessary to ground the device, so electrolytic corrosion can be avoided.
The device is mounted on the suction side of the pump. In the section between the pumping equipment and the connection point, all elements that can contribute significant hydraulic resistance into the system. We connect the make-up line to the circulation circuit of the entire system.
Closed tank
The expansion tank belongs to the auxiliary equipment, but without this device, the efficient operation of the heating system is impossible. For the network to function properly, right choice and setting the parameters of all its elements. One of the most important indicators in this case is the pressure in the expansion tank.
Why is this design needed?
Before talking about the functions and settings of the expansion tank, it is necessary to understand the types and principle of operation of this equipment. Why is such a design needed in the heating system? The main task of the device is to compensate for thermal expansion in the network. Indeed, during heating and cooling, the coolant changes its density and volume.
Note! If this device is not installed in the engineering network, as it heats up, the water will increase in volume and affect the walls of pipes and radiators. With a strong increase in water pressure, the system can simply break. Installing an expander allows you to save not only the pipeline, but also the boiler. After all, his work is initially calculated for a certain pressure of water in the system.
Expansion devices may vary in volume. When choosing a model that is suitable in terms of technical parameters for a particular network, it must be borne in mind that the volume of this element must be at least 10% of the volume of the coolant circulating in the system. To perform such a calculation, the volume in the radiators, pipes and boiler is summed up. The easiest way to determine volume is during system pumping. It should be remembered that a volume of 10% is a minimum, but it is better to take a model with a small margin.
Expansion tanks for wall-mounted gas boilers should be mentioned separately. Most modern wall-mount models have an integral device mounted on the back or side wall and equipped with a nipple. The nipple is pressurized.
Device and principle of operation
All types of expansion tanks have the same device. Inside the metal case there are two rolled compartments. On one side there is a nipple, and on the other - a neck for connecting to the pipeline. Inside the body is a diaphragm. In an empty container, it will take most volume, while the rest of the space is filled with air.
During the operation of the system, the coolant heats up, increases in volume, and its excess enters the cavity between the housing and the diaphragm. When the temperature of the water in the system decreases, its volume decreases, and the injected air squeezes it back into the pipeline.
Installing the expansion element
Boiler equipment is designed to operate at a certain pressure of water. This means that there must also be a certain pressure in the expansion tank for its normal operation. It is supported by air or nitrogen, which is filled with the case. Air is pumped into the tank at the factory. During installation, care must be taken to ensure that no air is released. Otherwise, the device will not function.
The pressure is monitored with a manometer. The running arrow of the device indicates that the air has come out of the expander. In general, this situation is not a serious problem, since air can be pumped through the nipple. The average water pressure in the tank is 1.5 atm. However, they may not be suitable for a particular system. In this case, the pressure must be adjusted independently.
Normal indicators - by 0.2 atm. less than in the system. It is strictly not allowed to exceed the pressure in the expansion tank compared to this indicator in the network. In such situations, the coolant that has increased in volume will not be able to enter the tank. The tank is connected to the pipeline through the connecting size.
It is important not only to connect the expansion tank correctly, but also to choose the right place for its installation. Although modern models, can be mounted anywhere, experts advise installing this element of the system on the return line between the boiler and the pump.
To ensure the maintainability of the structure, a ball valve is installed on the pipe through which the expander tank is connected. In the event of equipment failure, shut-off valves will allow it to be removed without pumping the coolant out of the system. During operation of the system, the valve must be open. Otherwise, the pressure will rise sharply in it, and it will leak at its weakest point.
Installation in a boiler room
AT open systems ah s natural circulation coolant tanks of other types are installed. Such a tank is an open container, usually welded from sheet steel. It must be installed at the highest point of the engineering network.
The principle of operation of such an element is very simple. As it increases in volume, the liquid is forced out of the pipes, rising along them with air. Cooling, the coolant returns to the pipeline under the action of gravitational forces and natural air pressure.
Why does pressure drop?
The pressure in the expansion tank must be constant, but situations where it drops during system operation are not uncommon.
There are several reasons why blood pressure may drop:
- Coolant leaks. Most often, a similar problem occurs in systems where not water, but antifreeze is used as a coolant. Such liquids are able to penetrate into the smallest cracks, causing leaks. In this case, it is necessary to eliminate the leak and fill the tank with air.
- Pressure drop in the boiler. With a significant decrease in performance, it is necessary to contact specialists. If the pressure decreases slightly and equalizes after the system is started, it can be operated, since such failures do not cause harm.
Pressure setting
The water pressure in the expansion element of the heating system is an adjustable parameter. The setup is quite simple, and all the steps can be done independently.
To configure the required parameters, you need the following:
Connection principle
- Make a calculation and determine the required indicators - by 0.2 atm. less than in the system.
- Set these indicators before installing the tank in the system by releasing air or pumping it through the nipple.
- Connect the container to the pipeline and fill the system with water. This should be done slowly, monitoring the pressure indicators in the pipes and tank. The coolant should be pumped until the pressure indicators are equal.
- After that, it is necessary to connect the pumping equipment and continue pumping the coolant. Water must be pumped in until the tank reaches the operating pressure calculated before installing the network. This will ensure that a reserve volume of water enters the housing.
- The first start-up of the system must be carried out in the maximum temperature mode. Under this condition, the volume of the coolant increases by the value of the specific increment. This ensures that an amount of water equal to its capacity enters the tank. The pressure in the tank rises to the maximum.
Conclusion
The expansion tank is the most important additional element in any heating system. If for open systems with gravitational circulation it is enough to install a simple open reservoir at the top point, then for complex closed systems installation of industrial models is required.
These containers are hermetically sealed. During production, air is pumped into the housing to maintain the pressure necessary for the normal functioning of forced circulation systems. You can set the desired pressure indicators yourself using a pressure gauge and a conventional automobile compressor.
Similar posts
An expansion tank for water supply, the principle of operation and device, types and features are considered in detail. The criteria for choosing an expansion tank are presented, the disadvantages and the main purpose are considered.
Figure 1: Types of expansion tanks
The most important condition in the water supply system is the optimal support of water pressure. To ensure the correct pressure in the expansion tanks, compensators are used to even out the loads on pipes and equipment. Water is used not only in technical, but also in food purposes, so the tank and the membrane on the inside are made of a special material that does not change the taste and smell of water. This material must comply with sanitary and hygienic requirements and must have a quality certificate. An expansion tank for water supply systems compensates for water hammer, which greatly increases the life of pumps and pipelines.
Expansion tank device
Inside the expansion tank there is a rubber membrane that divides the tank into two chambers: air is pumped into one chamber, and the other chamber remains empty. In an empty chamber after installation and start of heating, the flow of coolant will begin. In another chamber, where air is pumped, the required volume will be restored. When the liquid cools, it is forced back into the water supply system. Thus, a constant, necessary pressure is kept in the pipes, which is why the system always works stably, there are no overloads and pressure surges.Figure 2: Expansion tank dimensions
The water from the well is under pressure, and at this time the membrane increases, the volume of air decreases, and some pressure is created. The pump turns off when the pressure reaches the required level. Water is consumed, the pressure drops accordingly, and the pump turns on to maintain pressure. The disadvantage of the expansion tank is an irrational method of temporary storage of water. The Dutch were the first to propose the use of expansion tanks with a membrane. Today, closed expansion tanks are very aesthetic and have a different design.
Figure 3: Expansion tank in action
The membrane expansion tank for water supply also has the disadvantage that the membrane cannot be replaced with such a design. If the heating system is working properly, then the liquid expands when the water starts, and otherwise the pressure fluctuations are smooth. The membrane of such a tank is made of high quality material and lasts a very long time.
Figure 4: Diaphragm expansion tank for water supply
Advice! Do not forget to check the air pressure before each heating season. For systems that have large volumes, it is best to use a stationary pressure gauge. (See also: )
With the help of a membrane expansion tank, hydrodynamic shock is compensated, which greatly reduces the frequency of pump operation. This design increases the service life and saves electricity. When the coolant is heated or cooled, the system remains intact. This compensates for the amount of change and it is for this purpose that a membrane expansion tank is installed. Even during a power outage, the reserve tanks have a fire extinguishing function. It is possible to use membrane tanks not only in domestic systems, but also in industrial ones, since the working pressure is calculated up to 16 bar. Hydraulic accumulators can be horizontal and vertical, open and closed. In addition, they differ in terms of water volume and operating pressure.
Volume of the tank
In order to find out the volume of the tank, you need to calculate the initial air pressure in the tank and the working pressure using the formulas, at maximum load. But it will be enough for the buyer to know that the volume of the tank is 1 to 10 of the volume of the coolant that is located in the system.Figure 5: Calculation of the volume of the expansion tank
Important! If the volume of the tank is not correctly selected, the heating system will not last long. Even with the most high temperature heating, the pressure in the heating system must in no case exceed the permissible one. (See also: )
Expansion tank for water supply, installation instructions are attached to each tank. There you need to look at the features of choosing an expansion tank, depending on the needs and characteristics of the heating system.
Expansion tanks of open type
They are installed at the highest points of the heating system: on the roofs of buildings or attics. The thermal expansion of the coolant does not allow water to boil, and if a leak occurs, the heating system is replenished with water. To date, tanks open type few places are installed, because they have some disadvantages:- too large structure;
- installed at a high point in the heating system, and for this it is necessary to purchase additional pipes (there will be heat losses); (See also: )
- air enters the heating system through the tank, corrosion forms on the heating devices and on the heating systems of some parts;
- cannot work stably under high pressure.
Figure 6: Diagram of the expansion tank
- Frame;
- Water level;
- Cold water pipe;
- Downpipe;
- Safety valve;
- Shut-off valve;
- The highest point in the pipeline riser.
Expansion tanks of closed type are used:
- in a heating system that works with autonomous heat sources;
- in a heating system that is connected to centralized networks compiled according to independent schemes;
- in a system that is connected to a solar collector and pumps;
- in a system connected to cold and hot water supply.
Expansion tank selection
It is necessary to choose an expansion tank taking into account all the features of the system. First you need to choose the required volume, choose the design, decide on the material of the membrane. It is also worth paying attention to the weight of the product, which is why the indicator can determine the quality of the reliability and durability of the expansion tank. It is better to purchase well-known brands, as they will be able to provide the heating system with long-term operation and prevent breakdowns in the system. The installation of an expansion tank for water supply and the price for it will please everyone who needs to install such a tank.The use of materials is allowed only if there is an indexed link to the page with the material.
Often, plumbing systems in the private sector are unstable: significant pressure drops are possible, which becomes a real problem for modern household appliances. To compensate for pressure fluctuations in water pipes most often, a membrane tank is used for water supply.
Membrane tanks are tanks of various capacities, made of metal and equipped with a rubber membrane. There are two types of membrane expansion tanks on the market: with a fixed (non-replaceable) rubber partition and a replaceable one. Their task is to accumulate a certain amount of water and release it at the right time under the right pressure, preventing excessive load in the system circuit and reducing the risk of accidents.
Membrane tank device with a fixed rubber baffle
The principle of operation of the membrane tank: after switching on, the pump pumps water into the water chamber, the volume of the air chamber decreases, and the pressure in the tank increases accordingly. When the pressure exceeds the allowable mark, the pump will turn off until it decreases again as a result of water intake (water is supplied to the consumer directly from the tank). Pressure control and adjustment of the operating range relay is carried out using a pressure gauge.
What to look for when choosing a tank
When selecting a membrane tank for water supply, one should take into account the number of users of the system, the intensity of water consumption, and its total amount. All this affects the main parameters.
The pre-pressure in the membrane tank is an important parameter. Usually, the manufacturer sets it to no more than 4 bar, and an adjustment takes place on the spot. The service life of the membrane and the reliability of the entire system depend on the correct setting. The preliminary pressure must be measured before installation with an empty tank, it must be lower than the start pressure of the pump.
The maximum and actual volume of the membrane tank do not match. The maximum is no more than 75% of the total volume, and the actual one is much less. So, if the pressure difference between turning off and turning on the pumping equipment is in the most acceptable for autonomous heating range of 2-2.5 bar, the actual volume of water will be about 30-35% of the total capacity. It should be noted that the greater the difference between the turn-on and turn-off pressures of the pump, the greater the actual volume of the membrane tank.
The minimum allowable volume of the membrane tank depends on the intensity of water intake, on the maximum allowable number of pump on / off per hour and on the pressure at which they will be carried out. It can be determined (approximately) by the following formula: V = 2Q/N, in which V is the volume, m3; Q is the expected water intake, m3/h;
N is the allowable number of pump starts per hour. It is important to know that a tank whose volume is slightly larger than the minimum allowable will help extend the life of the engine of pumping equipment.
Short installation instructions
If you want to install a membrane tank for water supply - the instruction should be contained in the technical documentation. Let's consider just a few points.
It is most convenient to install a membrane tank before branching the water supply
- It is most convenient to install a membrane tank before branching the water supply. In the room, it is necessary to provide for the possibility of draining water and feeding the system. The air temperature in the room must be above zero, freezing of water is not permissible.
- The fixing point must have sufficient load-bearing capacity. The membrane tank should not experience additional static load from other units, pipes, etc.
- To install tanks with a volume of 8 to 30 liters, you will need a special wall mount, which is characterized by increased strength. And large volume tanks are best installed on legs.
- Before installation, you must once again make sure that the technical calculation is made correctly. Be sure to familiarize yourself with technical specifications equipment that is on its body, and not to exceed the maximum allowable pressure both in the air and in the water chamber when setting the preliminary pressure and during operation.
- The tank must be grounded to avoid electrolytic corrosion.
- It is advisable to install a check valve at the inlet to the tank, if it is not provided for in the design of the pump, and at the outlet - a pressure gauge to control pressure and an automatic valve to release air.
- If the tank is not originally equipped shutoff valves, which is required during the technical inspection, for example, it must be installed at the installation site.
Membrane tanks have a lot of advantages. For example, when using them, water pollution is excluded, they have a larger usable volume than others, are easy to install and practical. But their installation and operation will require compliance with safety regulations. It is better to entrust the installation of a membrane tank to a specialist.