A diaphragm seal system in vacuum pressure process must master a significant challenge ? Tempting must deliver a reliable measuring result, even though the pressure drops and the temperature rises at the same time. The exemplory case of a chemical company producing phthalic anhydride (PA) implies that it is in no way self-evident that requirement can be met on a consistent basis.
PA is primarily used as a plasticiser for plastics. However, it 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, followed by vacuum pressure distillation process.
Critical phase for pressure measurement
In this technique, the critical phase for pressure measurement occurs in the distillation column. There, the process temperature can rise to a lot more than 230 �C as the pressure drops to 100 mbar abs. With this type of contrary action, the conventional installed measurement technology reaches its performance limit relatively quickly, which the aforementioned manufacturer was forced to find out ? all instrumentation showed a measurement deviation beyond your defined tolerance after only week or two.
Hidden 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 obtain a measuring solution that would also fulfil its task with the required accuracy in the long term under the conditions described. WIKA then drew on its in-depth expertise to design a diaphragm seal system for the vacuum process, comprising an activity 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 and also 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 too little can destabilise the volume balance of the diaphragm seal system and thus impair its function. Consequently, correct measurement would no more be guaranteed.
Test under application conditions
After cleaning, all elements 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 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 can be found on the WIKA website. If you have any questions, your contact will gladly help you.
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Just how do diaphragm seals work?
Watch the following video to learn more about the functionality, application areas and advantages of diaphragm seals: