A diaphragm seal system in a vacuum process must master a significant challenge ? it must deliver a trusted measuring result, even though the pressure drops and the temperature rises as well. The exemplory case of a chemical company producing phthalic anhydride (PA) demonstrates 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, additionally it is 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 technique, the critical phase for pressure measurement occurs in the distillation column. There, the procedure temperature can rise to more than 230 �C as 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 find out ? Disadvantages showed a measurement deviation outside the defined tolerance after only fourteen days.
Diaphragm seal system adapted in every 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 business 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 create 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 elements of this measuring system were selected specifically for the application. 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 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 volume balance of the diaphragm seal system and thus impair its function. Because of this, correct measurement would no longer be guaranteed.
Test under application conditions
After cleaning, all parts of the diaphragm seal system were first fully welded into a single unit as usual, accompanied by the filling and adjustment of the machine. Before delivery, however, there was 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 process suitability of the measuring system.
Note
Further information 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 following video for more information about the functionality, application areas and advantages of diaphragm seals: