Features The CAL-PRO expansion vessels absorb the water volume variations in closed heating systems maintaining constant pressure, helping to reduce energy consumption. The broad range available meets the requirements of various heating systems. Technical Information capacity: from 4-900 litres Crimped or welded carbon steel shells Synthetic SBR rubber according to DIN 4807-3 norms suitable for every capacity for maximising tank drawdown. Vessels are painted externally with long-lasting epoxy polyester