The diaphragm vessel (a.k.a. diaphragm expansion tank) is a key element in protecting heating, cooling and hot water systems from excessive pressure rise. Its construction is a steel tank divided inside by a flexible diaphragm (diaphragm) into two chambers: water and gas (usually filled with compressed air or nitrogen). This design allows it to take on the increased volume of water that occurs due to thermal expansion - when the water in the system heats up, its volume increases and the membrane flexes, allowing some water into the tank and keeping the pressure within safe limits . As a result, the system works properly, and the safety valve does not drop water every time it gets hotter.