What to Consider in Expansion Tank Usage
When expansion tanks are activated, the control of the pressure of the air inside is the most important issue. Around 4 bar of air is pumped into the expansion tanks during production, but the pressure inside the tank needs to be adjusted according to the conditions of the building at the usage location.
There are formulas for calculating the amount of air to be pumped into the tank. However, in addition to the formulas, it is also possible to calculate more easily with a logical chain. The pressure that should be in the tank can be found by answering three simple questions. There is a slight difference in finding the initial gas pressure of the expansion tank used in heating installations and the initial gas pressure of the expansion tank used in hydrophore installations.
Let's first find the initial gas pressure of the expansion tank to be used in the heating installation:
Why do we use the tank?
- To absorb the pressure of water expanding with temperature. So, no water should enter the tank when the system is cold.
What pushes the water into the tank when the system is cold?
- It is the pressure of the water in the building's system.
What is the value of this pressure?
- It is equal to the building height (static pressure).
In this case, if the estimated height of the building is found, the static pressure can be easily calculated from here.
Now let's find the initial gas pressure of the expansion tank to be used in hydrophore installations:
Why do we use the tank?
- To store the water pushed by the hydrophore and then to take water from this storage tank in small usages and not to run the pump frequently. So, no water should enter the tank when the hydrophore is not running.
What pushes the water into the tank?
- It is the pressure of the water in the system at that moment.
What is the value of this pressure?
- It is the setting value of the pressure switch that the hydrophore automatically starts to operate.
As seen, the initial gas pressure of the tank should be equal to the static height in heating systems and to the starting pressure of the pressure switch in hydrophore systems. In practice, by pumping approximately half a bar less air into the tank than these values we found, some water is ensured to always be present in the tank. Because, if there is no water left in the membrane, the membrane can stick together and dry. Therefore, it is beneficial for the membrane to always be wet.
The tank air should be checked frequently. There are places in tanks where air leakage may occur, such as bottom flange, top suspension flange, and valve. Bolted connections can loosen over time due to constant vibration in the environment. Air leakage from the loose connection takes no more than half a day. In apartment buildings, if possible, the pressure inside the tank should be checked once a week, if not, at least once a month. A tank that has leaked air serves no function. The membrane sticks to the tank and the tank turns into a "pipe with a very wide diameter." It starts to behave like a solid surface.
It is meaningless to measure the air pressure of a tank with water inside. This is the most common mistake. Users or service personnel look at the pressure gauge while the systems are running. In this case, naturally they read a pressure amount equivalent to the operating pressure and assume that there is enough air in the tank. This is wrong. Even if there is only as much air as a deodorant can in the tank, pressure is read on the pressure gauge. However, since the amount of air is very small, most of the tank always remains filled with water. The useful volume of the tank decreases significantly. Tank air must be measured while the tank is empty. When the system starts operating and the tank starts to fill with water, the pressure gauge no longer reads the pressure of the air inside, but starts to display the pressure of the system.