Expansion tank for open heating: device, purpose, main types + tips for calculating the tank

Alexey Dedyulin
Checked by a specialist: Alexey Dedyulin
Author: Oleg Zubarev
Last update: May 2019

In today's realities, an expansion tank for open heating has long and irrevocably lost the competition of a more modern and efficient closed tank.

Nevertheless, obsolete equipment is actively used. And in a number of situations it even has some advantages over technological membrane tanks.

In this material we will analyze its purpose and design features, as well as get acquainted with the principle of work and the rules for calculating this type of tank.

Purpose of the tank in open type systems

The specified device is used in heating systems to prevent its breakdowns with an increase in the volume and pressure of the coolant, which occurs during heating.

To be precise, when the temperature of the water circulating in the system increases from 5 to 100 ° C, its volume becomes 4% more. And this is a lot, since there is nowhere to go in her pipes and radiators - there is no free space there.

Open tank
Excess coolant is squeezed into the open expansion tank from the heating system, which eliminates the breakdown of its parts as a result of increased pressure. Which arises because water cannot be squeezed, and it itself increases markedly in volume with increasing temperature. After cooling, the coolant returns to the heating system

As a result, several hundred grams in a small heating system or several liters in a sufficiently large system increase the pressure to critical values ​​and lead to powerful water hammer.

What entails the extrusion of gaskets, the breakdown of fittings, radiators and expensive repairs - all this at the most inopportune moment.

And after the coolant temperature decreases, its excess again becomes necessary for the effective functioning of the system, so they must be returned, and in full. In the event of evaporation, the fluid must be replenished.

Characteristics of an open tank

Such tanks are extremely simple - an ordinary bucket, a specially made container from improvised materials, a canister, or something similar can always be used as an expansion tank.

Design features of the tank

The main design requirements are:

  • availability of sufficient volume;
  • lack of tightness.

That is, even the absence of a cover is allowed, although it is desirable - it protects dirt particles from entering the heating system.

The tank, which is planned to be used as an expansion tank, must be equipped with a pipe to which it is connected trumpet from the heating system. This is the only mandatory fixture.

Expansion tank design
The design of any expansion tank is extremely simple - it is an ordinary tank equipped with one or more inputs / outputs. That allows excess fluid to accumulate, merge. The most technologically advanced reservoirs are equipped with a water supply, a drain valve, which is needed to transport water to the sewer with too large volumes

But for comfort and to eliminate minor troubles, it is advisable to use the following accessories:

  • Overflow hose or pipe - such a structural element is necessary in case of overfilling of the expansion tank. That is, this structural element, diverting liquid into the sewer or simply outside the building, eliminates the possibility of flooding.
  • Water pipe - it is necessary to replenish the heating system with water. It is quite possible to do without it, but it should be understood that this procedure will have to be carried out with a bucket in hand. Although in the latter case, the design will be cheaper.

Since expansion tanks are often installed in attics, you should take care of its thermal insulation. That eliminates the freezing of the liquid and the failure of the entire system.

As a heat carrier, only ordinary water can be used. Because modern effective antifreezes in open tanks evaporate quickly. Which leads to a significant increase in the cost of the entire room heating procedure.

In addition, the vapor of antifreeze is almost always toxic, which affects the health of residents. We talked more about the types of coolants for the heating system and their features in this stuff.

Form and material of manufacture

The shape of the tank does not matter, so it can be any:

  • round;
  • rectangular;
  • trapezoidal etc.

The material of manufacture can be any metal or even plastic, but since the coolant can be heated to significant temperatures, it must be heat-resistant.

The principle of operation of the expansion tank
This figure helps to understand the principle of operation of the expansion tank. The image on the left shows the coolant in a cold state. He has an excess of the provided volume. But, when warming up begins (figure on the right), then excess water will soon appear. In fact, there is not much excess fluid, but this is enough to find a weak spot in the system and form a leak or cause equipment damage

On sale there are various options for open expansion tanks, among which it is easy to choose the most suitable. Or make an improvised tank from improvised materials that will play the role of an expansion tank.

The principle of operation of the device

The expansion tank is part of the simplest heating systems operating according to the laws of physics. When the movement of fluid through pipes and radiators is carried out by gravity, the pressure differential provides energy for this.

In order not to interfere with the natural heat exchange and the water circuit, the expansion tank should be installed at the highest point of the entire heating system, while the boiler should become the lowest. We talked more about installing and connecting the tank in this article.

Otherwise, the presence of a tank will not give the desired effect. That does not protect against increased pressure, water hammer and subsequent breakdowns.

Design features of expansion tanks
An important advantage of open expansion tanks is their availability. For example, the tank can even be made from improvised materials, which are enough in summer cottages, in the utility rooms of private houses. Any metal or plastic container of the desired size can become expansion, as evidenced by the photo

The tank itself with a cold coolant does not take any part in the operation of the heating system.

Everything changes when the liquid is heated to significant temperatures and creates excess pressure in the pipes, radiators, since in such situations its excess is actively created and squeezed out into the expansion tank. Where it is until the coolant cools down, after which it flows by gravity back into the pipes and radiators, the boiler.

The described procedure is performed cyclically, that is, throughout the entire period of operation of the tank.

Due to the fact that the heating system is openAs the tank itself, compensation for the effects of expansion cannot be performed without human intervention.

The reason is that the coolant, being in direct contact with air, evaporates, and the more it heats up, the more actively this procedure occurs.

As a result, the user has to regularly monitor the available water level. And add it as needed.

The indicated operation is performed using a bucket or other container of water. This is unpleasant, therefore, the system can be automated by organizing the supply of water from the water supply system, and from any: local or centralized.

What are the expansion tanks
You should know that the geometric shapes and accurate calculations in the case of an open expansion tank are absolutely not important. The main condition for effective operation is the placement at the highest point of the system and the presence of a sufficient volume of capacity to the overflow pipe

In addition, using additional equipment, the described procedure can be made completely autonomous.

But in this case, the most important advantages of all open tanks and heating systems are lost:

  • cheapness;
  • complete autonomy, that is, independence from operability, serviceability and the presence of any engineering systems in the room.

All processes in an open tank occur according to the natural cycle, without the help of pumps and other equipment.

As a result, in order for the expansion tank to be guaranteed to be useful, the dimensions of the system itself must be moderate, that is, you should not use it to heat cottages and buildings with an area exceeding 100 m².

Placement of expansion tanks
The optimal location for expansion tanks is warm attics. Since there is guaranteed to be the highest point of the system, and even such a solution allows you to hide the design with low aesthetic properties away from the eyes

If this rule is ignored, this can lead to significant financial losses, since a number of alterations will have to be made to ensure the efficiency of the tank and the entire system as a whole.

In addition, altitude should be limited. Since it is very problematic to achieve the expected result when trying to heat more than a two-story building in this way.

How to make a calculation?

As mentioned above, any expansion tank used for heating an open type is notable for its simplicity of design and manufacture. And the calculation of the dimensions of such a product is no more complicated.

Why you can use the formulas or the method consisting in the approximate calculation of the working volume of the tank.

Formulas for calculating tank volume
An example of using the formula to calculate the desired tank volume.Based on the real volume of water circulating in the circuit, only its increase is calculated when heated to a certain temperature, rounding up. Then they add the result with the volume of coolant in the heating system and add an arbitrary amount of liters “in reserve”

In reality, in order to determine the necessary tank capacity, the owners of a small country house formulas are used extremely rarely. Most often, the approximate volume of the expansion tank is calculated, to which any number of liters can be added for insurance.

Reason: in the case of open tanks, excess volumes do not significantly affect the cost, and in some cases they do not lead to higher prices.

As a result, the entire calculation of capacity is reduced to the determination of 10% of the total coolant volume, which should be its minimum value of the expansion tank.

The easiest way to do this is at the time of designing and creating a heating system, when all parameters of radiators, pipes and other structural elements are known or they are easy to recognize by taking measurements. And then just adding up the volumes of all the components.

Benefits of Open Expansion Tanks
Although open expansion tanks and the systems for which they are intended have long become obsolete, their availability and, most importantly, high autonomy make them popular in conditions far from ideal. For example, if there is a problem with a stable supply of electricity or the owners of the premises do not live there permanently

If the initial data are unknown, then the most practical way of calculating is the experienced one. Why do you need to drain all the water from the system, and then fill it with coolant on a new one.

At the same time, measurement should be made, which can be done using a counter or when using containers of known volume. After that, it remains to find out the necessary 10% of the coolant volume, which serve as a guideline in the manufacture or purchase of the tank.

Conclusions and useful video on the topic

The roller located below will allow a better understanding of what open expansion tanks are, how they are made and installed:

The following video is about homemade tanks for a heating system:

An open expansion tank is considered an outdated device, as is the whole kind of heating system in which it is used. That is, such equipment is ineffective, since its work is accompanied by impressive heat loss, and heating is extremely slow.

Nevertheless, complete autonomy, independence, ease of maintenance, and affordable cost make an open tank popular far from the stable conditions of large cities - in cottages, in villages, etc..

Do you have questions about calculating the tank or want to clarify other points that we did not mention in this article? Ask about the nuances you are interested in, ask your questions in the block below - our experts and other visitors to the site will help you figure it out.

If you have recently been engaged in the manufacture or installation of an open type tank, tell us about it in the comments section - your information will be useful for many beginners. Also add unique photos of your expansion tank.

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