The Intercyl internal expansion cylinder is designed to remove the need to install a separate expansion vessel, hence saving time and space. All Intercyl cylinders have an internal baffle which maintains an air gap that rises and falls with changes in pressure, this is the units own unique expansion vessel. Duplex Stainless Steel Tank 2 Year Manufacturer's Guarantee (T&Cs Apply) Low Heat Loss & Fast Recovery High Value Insulation Suitable for Most Domestic Systems Overheat Cut-Out Protection Suitable for Direct Electrical Heating Duplex Stainless Steel Tank 2 Year Manufacturer's Guarantee (T&Cs Apply) Low Heat Loss & Fast Recovery High Value Insulation Suitable for Most Domestic Systems Overheat Cut-Out Protection Suitable for Direct Electrical Heating