Used as protective devices designed to isolate pressure gauges, pressure transmitters, and pressure switches from potentially damaging process media, diaphragm seals provide effective solutions to protecting pressure instruments. Typically used in refining, petrochemical, and chemical plants, they can help extend the lifetime of various instruments by preventing contact between dangerous hot or corrosive media and the gauge.

Diaphragm seals were especially designed to meet the safety demand requirements of the process industry to offer the utmost of protection against harsh temperatures, variable pressure ranges, pulsation, vibration, aggressive chemicals, and steam.

Understanding How the Seal Actually Works

A diaphragm seal is usually connected to the measuring instrument using a direct connection or capillary. It is an elastomer or flexible metal diaphragm that keeps the process media from coming into contact with the workings of the gauge. The chamber between the diaphragm and the instrument contains system fluid, which transfers the pressure of the process media. When fluctuations in pressure of the process media occur, the change is transmitted across the flexible diaphragm through the system fill fluid, which is hydraulically transmitted to the measuring instrument.

Diaphragm seals are easily mounted onto gauges using threaded, flanged, in line, sanitary, or other types of connections, and in most cases, are made out of stainless steel. Others materials such as carbon steel and Hastelloy® C-276 can also be used for specific applications. There are also times that they are installed on pressure transmitters and switches that can be exposed to extreme conditions.

When You Should Use A Diaphragm Seal

Simply put, a diaphragm seal should be used whenever there is highly toxic or dangerous media present that could potentially harm an instrument. The usage of a diaphragm seal should be considered under other conditions, such as:

  • High-temperature media – Contains a cooling element that can protect the instrument, such as a diaphragm seal with an 8″ cooling tower that can tolerate temperatures of up to 750°F.
  • Viscous or crystallizing media – Reduces the number of connections in a process by minimizing internal cavities where clogs usually form.
  • Media with suspended solids – Minimizes clogging in process applications that include pharmaceutical, pulp and paper, food and beverage, chemical, and waste water.
  • When overpressure protection is required – There are seals available with continuous-duty contoured diaphragm beds for robust overpressure protection.

Corrosive media – Seals can be made using a variety of custom alloys, including PTFE, gold and silver, or carbon steel.

The original article can be found on Real Seal's website here.

For more information about diaphragm seals, contact Gallagher Fluid Seals.