4. The expansion vessel is a small tank used in a closed heating system to absorb excess coolant pressure, which can be caused by thermal expansion as the coolant is heated by the solar collector. The vessel itself is a small container divided in two by a rubber diaphragm. One side is connected to the pipe system. The other contains air under pressure and a Schrader valve for checking the pressure and adding air. When the heating system is empty or at the low end of the normal range of working pressure the diaphragm will be pushed against the inlet. As the water pressure increases, so the diaphragm moves compressing the air on its other side. The compressibility of the air cushions the pressure shock and it relieves pressure in the system that could otherwise damage the plumbing system. Used materials: -tank: stainless steel -membrane: EPDM-rubber
