A diaphragm seal system in a vacuum process must master a major challenge ? it must deliver a trusted measuring result, even though the pressure drops and the temperature rises as well. The example of a chemical company producing phthalic anhydride (PA) implies that it is in no way self-evident that requirement can be met on a frequent 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, followed by a vacuum 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 while the pressure drops to 100 mbar abs. With such a contrary action, the traditional 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 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 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, consisting of 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 specifically for the application form. Silicone oil KN32 was therefore selected because 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 one another exactly. With sensitive limit ranges, even one drop of liquid an excessive amount of or inadequate can destabilise the volume balance of the diaphragm seal system and thus impair its function. Due to this fact, correct measurement would no longer 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 machine. Before Unhurried , however, there is another crucial step ? in its laboratory, WIKA simulated vacuum pressure process for the diaphragm seal system relative to the customer?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. Should you have any questions, your contact will gladly help you.
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How do diaphragm seals work?
Watch the next video for more information about the functionality, application areas and advantages of diaphragm seals: