A diaphragm seal system in vacuum pressure process must master a major challenge ? it must deliver a reliable measuring result, even though the pressure drops and the temperature rises concurrently. The example of a chemical company producing phthalic anhydride (PA) demonstrates it is in no way self-evident that requirement could be met on a consistent 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 vacuum pressure distillation process.
Critical phase for pressure measurement
In this process, the critical phase for pressure measurement occurs in the distillation column. There, Clarity can rise to more than 230 �C while the pressure drops to 100 mbar abs. With this type of 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 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 business approached WIKA with the request for a measuring solution that would also fulfil its task with the mandatory accuracy in the long term under the conditions described. WIKA then drew on its in-depth expertise to create 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. 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 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 more 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, accompanied by the filling and adjustment of the machine. 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 client?s conditions and subjected it to a thermal ageing process. This test confirmed the process suitability of the measuring system.
Note
Money on the WIKA diaphragm seal systems are available on the WIKA website. If you have any questions, your contact will gladly assist you to.
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Just how do diaphragm seals work?
Watch the following video for more information concerning the functionality, application areas and advantages of diaphragm seals:g