Air dehydrating breathers are transparent hollow cylinder tubes which contain chemically pure silicon salt (silica gel) with a coloured indicator.
The air flows inside the transformer due to the thermal contraction of the oil mass and passes through the silica gel; the silica gel absorbs the humidity, indicating the saturation degree by changing color.
The salt contained in the breather, when saturated, can be easily removed and replaced.
The upper and lower parts are made of a non-porous corrosion-proof aluminum alloy casting. The hollow cylinder is made of PMMA (or tempered glass) and is protected by a stainless-steel frame with windows that allow the visual inspection of the silica gel color.
On the bottom side of the breather, a hydraulic valve (an oil pot inside the lower aluminum housing) prevents continuous air contact with the silica gel and only allows air to pass in both directions (inlet or outlet) when there is a pressure deficiency or excess inside the transformer conservator.