Things to Consider in Expansion Tank Usage
When commissioning expansion tanks, it is crucial to check the pressure of the air inside. Expansion tanks are typically pressurized to about 4 bar during production, but the pressure inside the tank needs to be adjusted according to the conditions of the building where it will be used.
There are formulas for calculating the amount of air to be pumped into the tank. However, it is also possible to calculate it more easily with a logical chain of reasoning. The required pressure in the tank can be determined by answering three simple questions:
Why do we use the tank?
- To absorb the pressure of the water expanding with temperature. This means that no water should enter the tank when the system is cold.
What forces water into the tank when the system is cold?
- The pressure of the water in the building's plumbing system.
What is the value of this pressure?
- It is equal to the height of the building (static pressure).
If the estimated height of the building is found, the static pressure can be easily calculated from here.
Now let's find the pre-gas pressure of the expansion tank to be used in the hydro-pneumatic system:
Why do we use the tank?
- To store the water pumped by the hydro-pneumatic unit and then to use the water from this reservoir in small quantities without frequently operating the pump. This means that no water should enter the tank when the hydro-pneumatic unit is not running.
What forces water into the tank?
- The pressure of the water in the plumbing system at that moment.
What is the value of this pressure?
- It is the set value of the pressure switch (pressure switch) at which the hydro-pneumatic unit starts operating.
As seen, the pre-gas pressure of the tank should be equal to the static height in heating systems and equal to the operating pressure switch in hydro-pneumatic systems. In practice, approximately half a bar less air is pumped into the tank based on these values found to ensure that there is always some water in the tank. Because if there is no water left in the membrane, the membrane can stick together and dry out. Therefore, it is beneficial for the membrane to always remain wet.
The tank air should be checked frequently. There are places in the tanks where air leakage may occur, such as the bottom flange, top suspension flange, and valve. Bolted connections can loosen over time due to constant vibration in the environment. Air escaping from a loose connection lasts no more than half a day. In apartments, the pressure inside the tank must be checked weekly if possible, or at least monthly if not. A tank that has lost its air is useless. The membrane sticks to the tank and the tank becomes like a "very wide pipe." It starts to behave like a solid surface.
It is meaningless to measure the air pressure in a tank filled with water. This is the most common mistake. The user or service person looks at the manometer while the systems are operating. In this case, naturally, they read the pressure equivalent to the operating pressure and assume that there is enough air in the tank. This is wrong. Even if there is as little air as a deodorant can inside the tank, pressure is read on the manometer. But since the amount of air is very small, most of the tank is always filled with water. The useful volume of the tank decreases significantly. The tank air must be measured when the tank is empty. When the system starts operating and water starts filling the tank, the manometer starts to show the pressure of the system, not the pressure of the air inside.