Diaphragm seal
Diaphragm seals are devices that are used in pressure measurement technology and prevent the medium from penetrating into the pressure measuring element. They are often used in conjunction with Bourdon tube pressure gauges or whenever the parts in contact with the medium are chemically attacked. They are also used when the medium tends to crystallize or polymerize , is highly toxic or harmful to the environment. They can also be used to thermally decouple the pressure measuring device from the medium.
In addition to the flange or membrane diaphragm seal design described below, special designs are also used, such as pipe or tongue diaphragm seals.
Flanged or diaphragm seal
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Diaphragm seals usually consist of a membrane that is clamped between two flanges . The flange facing the pressure measuring device is referred to as the upper part of the diaphragm seal, the one facing the measuring medium or pressure vessel as the lower part of the diaphragm seal (see figure above). So it is possible to make only the diaphragm seal lower part and the diaphragm in highly corrosion-resistant (and expensive) materials and not the complete pressure measuring system.
In addition to chromium-nickel steel types, the following are often used as membrane materials :
- Nickel-based alloys such as Hastelloy and Monel
- Refractory metals such as titanium and tantalum
- Precious metals like gold and platinum .
On the instrument side, the measuring system is evacuated and filled with a pressure transmission fluid. The elastic membrane transfers the pressure to the liquid and this transfers it to the actual pressure sensor . The sensor can be mounted directly on the diaphragm seal or connected via a capillary line, which makes it possible to install pressure measuring devices at a distance from the process connection point. As filling liquids are u. a. Silicone oil , glycerine or white oil are used.
Web links
- Jörg Kempf: Diaphragm seals protect measuring devices in difficult environmental conditions .
- Breunig, Jennifer and Kern, Heiko: Diaphragm seal systems for safety applications: Reduced risk .
- Example of a diaphragm seal in a pipeline for mash .
