An itinerant apparatus used as the unit of drying gas, it consists in four cylindrical pressure vessels, connected two by two and at vertical axis.
The operation is based on the presence, within each container, of grit silica gel which allows the drying of gases by trapping the water present in the gas itself. When the silica gel is saturated with water, automatically, without ever interrupting the drying process of the gas, there is the change of columns and for those saturated the process of regeneration of the silica gel begins. This operation is performed by making gas at 200° C transit in the containers which remove the water from the grit of silica gel drying it.