Diaphragm pressure gauges, also called sealgauges, are suitable for low pressure and overpressure measuring conditions.

Diaphragm pressure gauges are used to measure gases and liquids. They cover measuring spans from 10 mbar to 40 bars. The measuring element consists of one circular diaphragm clamped between a pair of flanges. The positive or negative pressure acting on these diaphragms causes deformation of the measuring element. The magnitude of the deformation is proportional to the pressure to be measured, and it is coupled to the pointer mechanism.

Diaphragm pressure gauges are considered as specialists in the process industries. They come into play when Bourdon tube pressure gauges reach the limits of their performance. One of the advantages of diaphragm pressure gauges is the measurement of low pressures.

Diaphragm pressure gauges can be recognised from the first look: From the flanges below the case, between which the elastic pressure element – the diaphragm element – is clamped. These instruments can measure pressures from as low as 16 mbar, with the maximum value at around 25 bar (for comparison: Bourdon tube gauges reach their lowest physically possible measured value at 600 mbar). The larger the diaphragm element, the lower the measurable pressure is, in accordance with the formula – pressure = force / area.

With pressures under 16 mbar, diaphragm pressure gauges hit their limits. For this case, their diaphragms would have to be exceptionally thin in order to achieve the required elasticity. Then, however, they would no longer remain reliably stable. This problem can be solved, though, with a special variation of the diaphragm pressure gauge: the capsule pressure gauge.

Capsule elements consist of two diaphragms welded together, which are generally loaded with pressure from the inside. This results in a double diaphragm travel. In this way, even the lowest of pressures can be measured without reducing the wall thickness. However, since the pressure chamber is not self-draining, capsule elements are not suitable for applications with liquid media.

Diaphragm pressure gauges measure gauge, absolute and differential pressure. In processing industries, they can be installed in applications with highly corrosive, viscous media.

Diaphragm pressure gauges are ideal for these harsh conditions because the media can clog the narrow pressure ports of threaded connections of Bourdon tube instruments as well as the internals of the tube.

To prevent such clogging, diaphragm pressure gauges are connected to the process with an open flange. This configuration provides a large pressure chamber, which prohibits media from settling.