Lasting accuracy for diaphragm seal systems for vacuum process

A diaphragm seal system in a vacuum process must master a significant challenge ? it must deliver a trusted measuring result, even when the pressure drops and the temperature rises at the same time. The exemplory case of a chemical company producing phthalic anhydride (PA) shows that it is by no means self-evident that requirement could be met on a consistent basis.
PA is primarily used as a plasticiser for plastics. However, additionally it is 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 a lot more than 230 �C while the pressure drops to 100 mbar abs. With such a contrary action, the traditional installed measurement technology reaches its performance limit relatively quickly, which the aforementioned manufacturer was forced to find out ? all instrumentation showed a measurement deviation outside the 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 company approached WIKA with the request for 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 because 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 each other exactly. With sensitive limit ranges, even one drop of liquid an excessive amount of or too little can destabilise the volume balance of the diaphragm seal system and thus impair its function. As a result, correct measurement would no more be guaranteed.
Punch 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 was another crucial step ? in its laboratory, WIKA simulated vacuum pressure 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 procedure suitability of the measuring system.
Note
Further information on the WIKA diaphragm seal systems are available on the WIKA website. Should you have any questions, your contact will gladly assist you to.
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