Considerations When Using an Expansion Tank
When commissioning expansion tanks, the most crucial issue is to control the pressure of the air inside. Approximately 4 bar of air is compressed in expansion tanks during production, but the pressure inside the tank should be adjusted according to the conditions of the building at the place of use.
There are formulas for calculating the amount of air to be compressed into the tank. However, 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 determining the initial gas pressure of the expansion tank used in heating systems and the initial gas pressure of the expansion tank used in hydrophore systems.
First, let's find the initial 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 expanding with temperature. Therefore, no water should enter the tank while the system is cold.
What pushes water into the tank while the system is cold?
- The water pressure in the building's plumbing.
What is the value of this pressure?
- It is equal to the height of the building (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 systems:
Why do we use the tank?
- To store the water pushed by the hydrophore and then take water from this tank in small uses without running the pump frequently. Thus, no water should enter the tank while the hydrophore is not running.
What pushes water into the tank?
- The water pressure in the plumbing system at that moment.
What is the value of this pressure?
- It is the setting value of the pressure switch (pressure sensor) when the hydrophore starts automatically.
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 compressing about half a bar less air to the tank than these values we found, it ensures that there is always some water in the tank. Because if no water remains inside the membrane, the membrane can stick together and dry out. Therefore, it is beneficial for the membrane to remain constantly wet.
The tank air should be checked frequently. There are places in tanks such as the lower flange, upper hanging flange, and valve where air leakage may occur. Bolted connections can loosen over time due to continuous vibration in the environment. Air escaping from the loose connection takes no more than half a day. In apartments, if possible, the pressure inside the tank should be checked weekly, if not, it must be checked monthly. A tank with escaped air serves no purpose. The membrane sticks to the tank and the tank becomes "a pipe with a very wide diameter." It starts to act as a solid surface.
It is meaningless to measure the air pressure in a tank containing water. This is the most common mistake. Users or service personnel look at the manometer while the systems are running. In this case, they naturally read the pressure equivalent to the operating pressure and assume that there is sufficient air in the tank. This is incorrect. The tank air must be measured when the tank is empty. When the system starts operating and water starts filling the tank, the manometer will start showing the system pressure, not the pressure of the air inside.