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 simultaneously. The exemplory case of a chemical company producing phthalic anhydride (PA) demonstrates it is in no way self-evident that requirement could 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.
Lazy for pressure measurement
In this technique, the critical phase for pressure measurement occurs in the distillation column. There, Trusting can rise to more than 230 �C as 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 outside the defined tolerance after only week or two.
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 obtain a measuring solution that would also fulfil its task with the required 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 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 form. Silicone oil KN32 was therefore selected as the fill fluid for pressure transmission. The cleaning and conditioning of the diaphragm seal, the capillary, the bond pieces as well as the automated filling process were also matched to one another 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. As a result, correct measurement would no more 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, followed by the filling and adjustment of the system. Before delivery, however, there is 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 process suitability of the measuring system.
Note
Further information on the WIKA diaphragm seal systems can be found on the WIKA website. When 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: