Bellows is a tubular elastic sensitive element that is connected by a collapsible corrugated sheet along a collapsible direction.Bellows are widely used in instrumentation, mainly used as a measuring element for pressure measuring instruments to convert pressure into displacement or force.The wall of the bellows is thin, with a high sensitivity, measuring range of tens to dozens of mpa.Its open end is fixed, the seal end is in free state, and use auxiliary spiral spring or reed to increase flexibility.Under the action of internal pressure, the work is elongated along the length of the tube, causing the activity end to produce a displacement that is related to the pressure.The active end drives the pointer directly to indicate the magnitude of the pressure.The bellows are often combined with the displacement sensor to form a pressure sensor that outputs electricity, and is sometimes used as a separator.Because the extension of the bellows requires a large volume change, its response speed is lower than that of bourdon tube.Bellows are suitable for measuring low pressure.

Bellows mainly include metal bellows, corrugated expansion joints, corrugated heat exchange tubes, diaphragm film boxes and metal hoses.Metal corrugated pipe is mainly used in the thermal deformation compensation pipeline, shock absorption, absorption pipeline settlement deformation, and so on, are widely used in petrochemical, instrumentation, aerospace, chemical industry, electric power, cement, metallurgy, etc.Other materials, such as plastic, have irreplaceable functions in media transportation, electric power threading, machine tools and household appliances.
Bellows is a kind of elastic element in pressure measuring instrument.

It is a cylindrical thin-walled, corrugated shell with multiple transverse corrugation. The corrugated pipe is elastic and can produce displacement under pressure, axial force, transverse force or bending moment.Bellows are widely used in instrumentation, mainly used as a measuring element for pressure measuring instruments to convert pressure into displacement or force.The wall of the bellows is thin, with a high sensitivity, measuring range of tens to dozens of mpa.In addition, the bellows can also be used as a sealed isolation element to separate the two media or prevent the harmful fluid from entering the measuring part of the device.It can also be used as a compensating element, using its volumetric variability to compensate for temperature errors.Sometimes it is used as elastic joint of two parts.The corrugated pipe can be divided into metal bellows and non-metal bellows according to the constituent materials.The structure can be divided into single layer and multi-layer.Single layer corrugated pipe is used more.Multi-layer corrugated pipe with high strength, good durability and low stress, used in important measurement.Corrugated tubes are generally made of bronze, brass, stainless steel, monel and inconel alloys.

The stress on the Rubber bellows is caused by the pressure in the system and the deformation of the bellows.The pressure creates a ring (circumferential) stress on the bellows, and a radial film and bending stress are produced at the side wall, trough and crest of the wave.The thin shell that cannot bend is sometimes called a thin film, and the stress that is ignored bending is called the membrane stress.Radial film stress and bending stress are produced when corrugated pipe is deformed.Bellows at work, some under internal pressure, some under external pressure, such as Rubber bellows seal expansion joint and metal hose in most cases the bellows under internal pressure, and used in the valve stem seal bellows under external pressure generally here mainly analysis the stress of bellows under internal pressure, the ability of bellows under external pressure generally higher than the internal pressure resistance ability.With the widely application of the corrugated pipe, corrugated pipe stress analysis of a large number of research and experimental verification, put forward a lot of calculation formula for engineering design, calculation program and charts.