The two halves of the vessel and the diaphragm are retained by a crimped collar to give a pressure tight seal on sizes 8 to 25 litre and on larger sizes by a welded joint. Non-replaceable diaphragm. Epoxy coated in grey. Suitable for flow temperatures up to 120 ̊C, resistant to ethylene orpropylene glycol mixtures and has low gas permeability.
In a closed heating system 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 diaphragm against the tank towards the inlet. As the temperature increases, the expanded water volume pushes against the diaphragm creating additional volume for the water to enter. When the temperature decreases, the pre-charge pressure forces the water from the tank and back into the main heating system. This maintains a constant pressure within the heating system helping to reduce energy consumption.
