Diaphragm seal

Diaphragm seals are devices that are used in the pressure measurement. They prevent the penetration of the medium into the pressure measuring element and are often used in conjunction with pressure gauges with Bourdon tube or whenever the the fluid contact parts are chemically attacked by this. They can also serve to thermally decouple the pressure gauge on the medium. Furthermore, they are used, if the fluid is prone to crystallization or polymerization, is highly toxic or environmentally harmful.

Diaphragm seals are usually made of a membrane which is clamped between two flanges. The pressure gauge facing flange is called a diaphragm seal upper part facing the measuring medium or pressure vessel as a diaphragm seal bottom. Thus, it is possible only the diaphragm seal bottom and the membrane in highly corrosion resistant ( and costly ) to execute materials and not the complete pressure measurement system. As materials for diaphragm seal bodies often nickel-based alloys such as Hastelloy and Monel, refractory metals such as titanium and tantalum, or even precious metals like gold and platinum are used.

Instrument side, the measuring system is evacuated and filled with a pressure transfer fluid. The elastic membrane transfers the pressure on the liquid and transmits it to the measuring device which can be mounted directly on the diaphragm seal, or a capillary. This makes it possible to spatially removed to install pressure gauges on the process connection point. When filling fluids are among others Silicone oil, glycerin, or white oil used.

In addition to the described design as a flange or diaphragm seals, special forms of construction such as pipe - or tongue pressure transmitter.