Lasting accuracy for diaphragm seal systems for vacuum process

A diaphragm seal system in vacuum pressure process must master a major challenge ? it must deliver a trusted measuring result, even though the pressure drops and the temperature rises at the same time. 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 frequent basis.
Dollar 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 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 process temperature can rise to more than 230 �C as 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 find out ? all instrumentation showed a measurement deviation beyond your defined tolerance after only fourteen days.
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 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 design a diaphragm seal system for the vacuum process, consisting of 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 designed 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 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 quantity balance of the diaphragm seal system and therefore impair its function. Because of this, correct measurement would no longer be guaranteed.
Test under application conditions
After cleaning, all elements of the diaphragm seal system were first fully welded right into a single unit as usual, accompanied by the filling and adjustment of the system. Before delivery, however, there is another crucial step ? in its laboratory, WIKA simulated vacuum pressure 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
Further information on the WIKA diaphragm seal systems can be found on the WIKA website. For those who have any questions, your contact will gladly assist you to.
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