A diaphragm seal system in a vacuum process must master a major challenge ? it must deliver a trusted measuring result, even when the pressure drops and the temperature rises as well. The example of a chemical company producing phthalic anhydride (PA) implies that it is by no means self-evident that this requirement could be met on a consistent basis.
PA is primarily used as a plasticiser for plastics. However, it is also used 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 vacuum pressure distillation process.
Critical phase for pressure measurement
In this process, the critical phase for pressure measurement occurs in the distillation column. There, the process temperature can rise to a lot more than 230 �C while the pressure drops to 100 mbar abs. With this type of contrary action, the conventional installed measurement technology reaches its performance limit relatively quickly, that your aforementioned manufacturer was forced to learn ? all instrumentation showed a measurement deviation beyond your defined tolerance after only week or two.
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 would 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 create a diaphragm seal system for the vacuum process, consisting of an activity transmitter (model IPT-20), a flange-type diaphragm seal with flush diaphragm (model 990.27) and a capillary.
All elements of this measuring system were selected designed for the application form. Silicone oil KN32 was therefore selected because the fill fluid for pressure transmission. Senseless 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 an excessive amount of or inadequate can destabilise the quantity balance of the diaphragm seal system and therefore impair its function. Therefore, correct measurement would no longer be guaranteed.
Test under application conditions
After cleaning, all elements of the diaphragm seal system were first fully welded into a single unit as usual, followed by the filling and adjustment of the system. Before Graceful , however, there is another crucial step ? in its laboratory, WIKA simulated vacuum pressure process for the diaphragm seal system in accordance with 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 assist you to.
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How do diaphragm seals work?
Watch the following video to learn more about the functionality, application areas and advantages of diaphragm seals: