A bellows is a tubular element made by connecting foldable bellows in a telescoping manner along the folding direction. Bellows are widely used in instruments and meters, primarily serving as measuring elements in pressure gauges to convert pressure into displacement or force. The wall of a bellows is thin and highly sensitive, with a measurement range of tens to tens of megapascals. The open end is fixed, while the sealed end remains free, utilizing auxiliary spiral springs or added elasticity. During operation, it extends along the tube's length under internal pressure, causing the movable end to displace in relation to the pressure. The movable end drives a pointer to directly indicate the pressure magnitude. Bellows are often combined with displacement sensors to form electrical-output pressure sensors and sometimes act as isolation elements. Due to the bellows' requirement for a larger volume change during expansion, their response speed is lower than that of Bourdon tubes. Bellows are suitable for measuring low pressure.