Interchangeable Membrane Pressure Tanks inside the vessels used in sanitary applications is a totally hygiene butyl membrane that will not taint the water with odor. The membrane used in heating and cooling systems is made of EPDM that is surrounded with nitrogen gas under pressure. • To pretect againts corrosion, the outer surfaces of the vessels are painted with electrostatic baked powder paint. The inner surface of the condensations tanks with changeable membrane is corrosion resistant as long as there is no damage to the membrane and the surface does not come into direct contact with water • Under normal conditions (no foreign particles being present in water and stich number being proberly selected) the closed pressure tanks have a very long lifetime.