In closed loop systems such as air conditioners, solar thermal systems, boilers, and floor heating, expansion tank is to absorb the expansion volume of this system due to temperature changes in order to prevent system's pressure from changing rapidly, reduce the number of pressure reliefs of the safety valve and the number of water feeding of filling valve.
As the system pressure is higher than the pressure of the pre-inflated gas inside the tank, there will be some working fluid entering the gasbag until a new balance is reached when the expansion tank works in the system.
When the system pressure rises again, there will be some part of working fluid entering the gasbag, compressing the gas between the gasbag and the tank, In this case, the gas is compressed and the pressure is raised, working fluid stops entering when gas pressure is the same as system pressure.
On the contrary, when system pressure drops, the pressure of working fluid in the system is lower than gas pressure between the gasbag and tank, water in the gasbag is replenished into the system by extrusion in order to increase system pressure.
Until the system working fluid pressure is equal to the gas pressure insde tank, the water in the gasbag is no longer coming out to the pipeline, maintaining a dynamic balance.
The expansion tank can not only keep the pressure stable in the closed system, but also protect the tank, circulating pump, pipeline and other equipment from damage, thereby prolonging the service life of the entire system.