Contents
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 high, the equipment wears out too quickly. To stabilize the pressure in the system, an expansion tank for heating is required. The device is simple, but without it, heating will not work for a long time.
Why do you need an expansion tank for heating
During the operation of the heating system, the coolant often changes its temperature – it either heats up or cools down. Of course, this changes the volume of the liquid. It either increases or decreases. Excess coolant is just forced out 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 systems of water heating – 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 heating a closed type. It is called closed because it is a sealed container, which is divided into two parts by an elastic membrane. Air is in one part, excess coolant is forced out into the other. Due to the presence of a membrane, the tank is also called a membrane tank.
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 heating pipes are connected. It does not even require a lid, although it may 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 leaky, the coolant evaporates and it is necessary to monitor its quantity – 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 that the system will become airy, which can lead to its breakdown.
More convenient automatic water level control. True, then in the attic, in addition to heating pipes, you will also have to pull water supply and also bring out the overflow hose (pipe) somewhere in case the tank overflows. 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 an expansion tank for heating: 10% of the volume of coolant in the system is calculated. You should have calculated 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, measuring it at the same time (put it through the meter). The second way is to calculate. Determine the volume of pipes in the system, add the volume of radiators. This will be the volume of the heating system. Here from this figure we find 10%.
Formula
The second way to determine the volume of an 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:
- the maximum pressure Pmax at which the system can operate (usually take the maximum pressure of the boiler);
- initial pressure Pmin – from which the system starts work (this is the pressure in the expansion tank, indicated in the passport);
- expansion coefficient of the coolant E (for water 0,04 or 0,05, for antifreezes 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 with them? If the system is open type, the answer is unambiguous – no. The cost of the container does not depend very much on the volume, plus you can make it yourself.
Expansion tanks for closed-type heating are worth counting. Their price depends heavily on volume. But, in this case, it is still better to take it 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 the second one. In total, they should give the required volume (the installation is no different).
What will cause the insufficient volume of the expansion tank
When heated, the coolant expands, its excess is 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 into the sewer.
Then, when the temperature drops, the volume of the coolant decreases. But since there is already less of it in the system than it 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 is operable. When the lower limit is reached, the equipment is blocked. If you are at home at this time, you can correct the situation by adding a coolant. If you are not present, the system may unfreeze. By the way, working at the limit also does not lead to anything good – the equipment quickly fails. Therefore, it is better to play it safe and take a slightly larger volume.
Tank pressure
In some boilers (usually gas boilers), 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 must be 0,2-0,3 atm lower than the working one.
The heating system of a low 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 pressure gauge, 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 released through it. The principle of operation is the same as that of an automobile spool – bend the plate with something thin, bleed air to the required levels.
You can also increase the pressure in the expansion tank. To do this, you will need a car pump with a pressure gauge. You connect it to the nipple, pump it up to the required readings.
All the above procedures are carried out on 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 tank of the heating system on site. Just be careful! It is necessary to check and correct 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 settings, it is important that the pressure on the boiler is zero. Therefore, we lower the water carefully. Then we connect the pump with a pressure gauge and adjust the parameters.
Where to put in the system
The 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 work more reliably. So the specific installation location 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 upwards, a tank is screwed onto it. If the wall does not allow you to put the container, you will have to make a knee, but the tank is turned up. Now we can assume that the expansion tank is installed.
But for the convenience of checking, it is advisable to put another tee after the tank, on the free outlet of which install a stopcock. This makes it possible to check the membrane tank without draining the entire system – it cuts off the tank. Turn off the tap, drain the water from the boiler. Check the pressure on the disconnected branch (in the boiler). It must be zero. After that, you can carry out all the rest of the configuration work.