A diaphragm seal system in vacuum pressure process must master a significant challenge ? it must deliver a reliable measuring result, even though the pressure drops and the temperature rises concurrently. The example of a chemical company producing phthalic anhydride (PA) demonstrates it is in no way self-evident that this requirement could be met on a consistent 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, accompanied 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 procedure temperature can rise to more than 230 �C as the pressure drops to 100 mbar abs. With Smug 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 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 business approached WIKA with the obtain 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 create 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 components of this measuring system were selected designed 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 bond pieces plus the automated filling process were also matched to one another exactly. With sensitive limit ranges, even one drop of liquid too much or too little 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 elements 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 was another crucial step ? in its laboratory, WIKA simulated a vacuum process for the diaphragm seal system in accordance with 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 are available on the WIKA website. In case you have any questions, your contact will gladly assist you to.
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How do diaphragm seals work?
Watch the next video to learn more concerning the functionality, application areas and benefits of diaphragm seals: