it consists of two identical shells made of fabricated mild steel with protective internal coating, demister screens of knitted monel metal wire and vapour condensers made up of aluminium brass U tubes expanded into rolled naval brass tube plates. Sea water is pumped through the control valve A to the second and then the first stage vapour condensers wherein it increases in before final heating to 80°C in temperature the steam supplied heat exchanger. pressurised, heated sea water flows through an orifice into the first flash chamber The whose low pressure corresponds to a saturation temperature less than that of the incoming heated sea water. Hence some of must be evaporated in order that its the water temperature can fall to around that which corresponds to the pressure in the chamber