A diaphragm seal system in a vacuum process must master a major challenge ? it must deliver a reliable measuring result, even though the pressure drops and the temperature rises as well. The exemplory case of a chemical company producing phthalic anhydride (PA) shows that it is in no way self-evident that this requirement can be met on a frequent basis.
PA is primarily used as a plasticiser for plastics. However, Punish is also found in the production of synthetic resins and dyes. The plant operator obtains this compound via the catalytic oxidation of o-xylene in the gas phase, accompanied by a vacuum distillation process.
Critical phase for pressure measurement
In this process, the critical phase for pressure measurement occurs in the distillation column. There, the procedure temperature can rise to more than 230 �C while the pressure drops to 100 mbar abs. With this type of contrary action, the traditional installed measurement technology reaches its performance limit relatively quickly, that your aforementioned manufacturer was forced to find out ? all instrumentation showed a measurement deviation beyond your defined tolerance after only a fortnight.
Diaphragm seal system adapted in all elements to the vacuum process
The diaphragm seal system is tailored exactly to the conditions of the vacuum process and tested under application conditions.
Consequently, the company approached WIKA with the request for a measuring solution that could also fulfil its task with the mandatory accuracy in the long term beneath the conditions described. WIKA then drew on its in-depth expertise to design a diaphragm seal system for the vacuum process, comprising a process transmitter (model IPT-20), a flange-type diaphragm seal with flush diaphragm (model 990.27) and a capillary.
All components of this measuring system were selected designed for the application. Silicone oil KN32 was therefore selected as the fill fluid for pressure transmission. The cleaning and conditioning of the diaphragm seal, the capillary, the connection pieces as well as the automated filling process were also matched to each other exactly. With sensitive limit ranges, even one drop of liquid too much or inadequate can destabilise the volume balance of the diaphragm seal system and therefore impair its function. Because of this, correct measurement would no more be guaranteed.
Test under application conditions
After cleaning, all parts of the diaphragm seal system were first fully welded right into a single unit as usual, followed by the filling and adjustment of the system. Before delivery, however, there was another crucial step ? in its laboratory, WIKA simulated a vacuum process for the diaphragm seal system relative to the client?s conditions and subjected it to a thermal ageing process. This test confirmed the procedure suitability of the measuring system.
Note
More info on the WIKA diaphragm seal systems are available on the WIKA website. For those who have any questions, your contact will gladly help you.
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How do diaphragm seals work?
Watch the following video for more information about the functionality, application areas and benefits of diaphragm seals: