The Bellows
The element consists of a thin walled tube of harmonica-like shape. The pressure is normally applied to the inside of the bellows. The bellows will expand in length when a pressure is applied. By means of a link and geared movement this deflection is converted into rotation of a concentric pointer to be indicated on a dial scale. Bellows pressure gauges are intended for measurement of very low pressure. They are mainly used in differential pressure gauges.