The basic operational principle of the closed expansion tank for preventing Water Hammering is the same as that of the air chamber. However, if the capacity of the closed expansion tank is large, there exists the possibility of problems in manufacturing and maintenance. A typical air chamber has a structure whereby air contacts and merges with water. On the other hand, a closed. It is made of general rubber (Butyl Rubber, EPDM). Because a hanging rubber pocket with an internal installation structure is used , the force always acts in the direction of gravity, and the rubber pocket can be damaged if even a bit of dust gets inside it.
If the internal rubber pocket is damaged, air may infiltrate the water, or be released out through the pipe. If compression fluid, air or nitrogen disappears from the inside, the closed expansion tank cannot provide any function for Water Hammering, except in the role as a simple water tank. However, the exterior of the closed expansion tank is generally made of steel, thus it is difficult to determine whether the internal diaphragm is operating properly or not. A “Safety device-equipped airtight expansion tank” has a safety device to externally monitor the internal diaphragm and ensure safe operation.