Manufactured in carbon steel with a two or three part weld construction. Pre-pressurised air chamber with synthetic rubber compound bladder. Sizes 60 to 1000 litres (except 140 litres) have a replaceable bladder. The internal surfaces of the vessel in contact with the water are coated against corrosion. External surfaces have a blue durable powder coated finish. Suitable for temperatures up to 70 ̊C, resistant to ethylene orpropylene glycol mixtures and has low gas permeability.
In a closed hot water circuit, the water cannot be compressed so any increase in volume, created by an increase in temperature, has to be accommodated by an expansion vessel. When water is cold, the pre-charge pressure forces the bladder to collapse until the pump is started when the bladder starts to inflate. As the temperature in the system increases, with the associated increase in pressure and volume, the expanded water enters the bladder creating additional volume and lowering the pressure. When the temperature decreases, the pre-charge pressure forces the water from the bladder and back into the main water circuit.
