Lasting accuracy for diaphragm seal systems for vacuum process

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 concurrently. The example of a chemical company producing phthalic anhydride (PA) demonstrates it is by no means self-evident that this 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, accompanied 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, digital pressure gauge can rise to more than 230 �C as 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 learn ? 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 business approached WIKA with the request for a measuring solution that could also fulfil its task with the required accuracy in the long run under 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 each other exactly. With sensitive limit ranges, even one drop of liquid an excessive amount of or inadequate can destabilise the volume balance of the diaphragm seal system and thus 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, followed by the filling and adjustment of the machine. Before delivery, however, there was another crucial step ? in its laboratory, WIKA simulated vacuum pressure process for the diaphragm seal system relative to the customer?s conditions and subjected it to a thermal ageing process. This test confirmed the process suitability of the measuring system.
Note
More info 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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