A diaphragm seal
is a flexible membrane that seals and isolates an enclosure. The flexible nature of this seal allows pressure effects to cross the barrier but not the material being contained in order to prevent damage or corrosion to the instrument.Materials
Since diaphragm seals need to be highly flexible, elastomers are commonly used, and include a wide variety of both general purpose and special rubbers. Elastomers are limited to low pressure applications and those that are chemically compatible with the various plastics and rubbers used.
Metal diaphragms of stainless steel (several grades), Carpenter 20, Hastelloy, Monel, Inconel, tantalum, titanium and several other metals are in common use where high pressure ratings and specific chemical compatibility are required. Flanged assemblies or flush welded versions are available. Applications
Diaphragm seals (also known as chemical seals or gauge guards) are also used to protect a process fluid from the pressure sensor. Examples of this use are:
- Sanitary processes (food, pharmaceuticals, etc.) where allowing process fluid to accumulate in the pressure port of the sensor would compromise the purity of the fluid (such as milk getting into the pressure port of a pressure gauge and spoiling)
- Very pure process fluids, where the metal surface of the pressure sensor might contaminate the fluid (such as copper ions from brass leaching into ultra pure water.)
- Pneumatic systems where small changes in pressures must be eliminated, such as those controlling air bearings.