A diaphragm seal is a device that consists of a diaphragm welded (or secured with screws) between two flanges and with the appropriate gasket to prevent liquid or gas leaks.
The diaphragm is a thin dividing membrane or partition, which acts as a barrier to a liquid or gas that may obstruct or corrode the sensing element of a pressure instrument. Can be used with pressure gauges, pressure transmitters or pressure switches.
The physical barrier (seal) between the instrument and the medium eliminates clogging and crystallization, which minimizes corrosion. A diaphragm seal also protects the instrument’s sensing element from high temperatures by dissipating and/or conducting heat.
How does filling work?
The pressure sensing instrument (manometer) is isolated from the process fluid by the flexible seal diaphragm. The empty space between this diaphragm and the pressure element of the instrument must be filled with an incompressible fluid, usually a type of oil. This fluid transmits the pressure applied to the flexible diaphragm to the sensing element of the pressure instrument (Pascal’s Principle).
Pascal’s Principle: The pressure exerted on an incompressible fluid in equilibrium within a container with non-deformable walls is transmitted with equal intensity in all directions and at all points of the fluid.
Diaphragm Seal Applications
- In processes where the fluids are corrosive and would attack the pressure sensing element.
- In processes where the fluids are loaded with solids or viscous and would block the pressure sensing element.
- Where the process fluid would solidify due to a change in process temperature.
- Where the process fluid must be contained in sanitary piping systems.
- In processes where the fluids are at a temperature that is too high to enter the pressure instrument.
Types of diaphragm seals
Given that there are numerous possibilities for using membrane separators, they cannot be covered by just one model. Over time, different designs proved to be particularly beneficial for certain cases. Taking into account the above, there are currently three basic types:
- Membrane separator.
- Tubular separator.
- Bulb separator.
