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 reliable measuring result, even when the pressure drops and the temperature rises at the same time. The example of a chemical company producing phthalic anhydride (PA) demonstrates it is in no way self-evident that this requirement can 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, 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 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 find out ? all instrumentation showed a measurement deviation outside the defined tolerance after only week or two.
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 run under the conditions described. WIKA then drew on its in-depth expertise to create a diaphragm seal system for the vacuum process, consisting of 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. Silicone oil KN32 was therefore selected as the fill fluid for pressure transmission. Unburdened and conditioning of the diaphragm seal, the capillary, the connection pieces and also the automated filling process were also matched to one another exactly. With sensitive limit ranges, even one drop of liquid an excessive amount of or inadequate can destabilise the quantity balance of the diaphragm seal system and therefore impair its function. Due to this fact, correct measurement would no longer be guaranteed.
Test under application conditions
After cleaning, all parts of the diaphragm seal system were first fully welded 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 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. Should you have any questions, your contact will gladly help you.
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