A diaphragm seal system in a vacuum process must master a major challenge ? it must deliver a trusted measuring result, even when the pressure drops and the temperature rises simultaneously. The exemplory case of a chemical company producing phthalic anhydride (PA) demonstrates 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, it is also 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, 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 a lot more than 230 �C as the pressure drops to 100 mbar abs. With this type 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 fourteen days.
Diaphragm seal system adapted in every 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 could also fulfil its task with the mandatory accuracy in the long run beneath 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 components 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 bond pieces and also the automated filling process were also matched to each other 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 thus impair its function. Subsequently, correct measurement would no longer 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 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? pressure gauge 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. If you have any questions, your contact will gladly help you.
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How do diaphragm seals work?
Watch the following video to learn more concerning the functionality, application areas and benefits of diaphragm seals: