A diaphragm seal system in vacuum pressure process must master a significant challenge ? it must deliver a reliable 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 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, 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 procedure 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 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 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 a process 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 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 plus the automated filling process were also matched to one another exactly. With Productive , even one drop of liquid too much or inadequate can destabilise the volume balance of the diaphragm seal system and therefore impair its function. Consequently, correct measurement would no more 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, accompanied by the filling and adjustment of the machine. 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 process suitability of the measuring system.
Note
Further information on the WIKA diaphragm seal systems can be found on the WIKA website. In case you have any questions, your contact will gladly assist you to.
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Just how do diaphragm seals work?
Watch the next video to learn more about the functionality, application areas and advantages of diaphragm seals: