Considerations When Using Expansion Tanks
When commissioning expansion tanks, it is important to control the pressure of the air inside. While around 4 bar of air is pumped in during production, the pressure in the tank must be adjusted according to the building's conditions at the usage location.
There are formulas for calculating the amount of air to be pumped into the tank. However, besides formulas, it is also possible to calculate more easily with a logical chain. The required pressure in the tank can be found by answering three simple questions. There is a slight difference between finding the front gas pressure of an expansion tank used in heating installations and that of an expansion tank used in hydrophore installations.
First, let's find the front gas pressure value of the expansion tank to be used in the heating system:
Why do we use the tank?
- To absorb the pressure of the water that will expand with heat. So, no water should enter the tank while the system is cold.
What pushes water into the tank while the system is cold?
- The pressure of the water in the building's installation.
What is the value of this pressure?
- It is equal to the building's height (static pressure).
In this case, if the estimated height of the building is found, the static pressure can easily be calculated from here.
Now let's find the front gas pressure of the expansion tank to be used in the hydrophore system:
Why do we use the tank?
- To store the water pumped by the hydrophore and then to take water from this tank for small uses and to avoid frequent pump operation. So, no water should enter the tank when the hydrophore is not working.
What pushes water into the tank?
- The pressure of the water in the installation at that moment.
What is the value of this pressure?
- It is the setting value of the pressure switch (pressure switch) that starts the hydrophore automatically.
As can be seen, the front gas pressure of the tank should be equal to the static height in heating systems and to the start-up pressure of the pressure switch in hydrophore systems. In practice, by pumping approximately half a bar less air to the tank compared to these values we found, some water is always ensured to be present in the tank. Because if no water remains in the membrane, the membrane can stick together and dry out. Therefore, it is beneficial for the membrane to be constantly wet.
The tank air should be checked frequently. There are places in tanks where air leakage can occur, such as the bottom flange, top suspension flange, and valve. Bolted connections can loosen over time due to continuous vibration in the environment. It takes a maximum of half a day for the air to escape due to loose connection. In apartment buildings, if possible, the pressure inside the tank should be checked weekly, otherwise, monthly without fail. A tank that has lost its air has no function. The membrane sticks to the tank and the tank turns into a "pipe with a very wide diameter." It starts to act like a solid surface.
It is meaningless to measure the air pressure of a tank that contains water. This is the most common mistake. Users or services look at the gauge while the systems are operating. In this case, they naturally read a pressure equivalent to the working pressure and assume that there is enough air in the tank. This is wrong. Even if there is as little air as a box of deodorant in the tank, pressure is read on the gauge. But since the amount of air is very little, most of the tank always remains filled with water. The useful volume of the tank decreases significantly. Tank air must be measured when the tank is empty. When the system starts operating and the tank starts to fill with water, the gauge will begin to show the system's pressure rather than the pressure of the air inside.