A diaphragm seal system in vacuum pressure process must master a significant 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) implies that it is by no means self-evident that requirement could be met on a frequent 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, followed 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, Breathtaking 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, which the aforementioned manufacturer was forced to find out ? all instrumentation showed a measurement deviation outside the 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 obtain a measuring solution that would also fulfil its task with the mandatory accuracy in the long term beneath the conditions described. WIKA then drew on its in-depth expertise to create a diaphragm seal system for the vacuum process, comprising 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 specifically 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 one another 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 therefore impair its function. As a result, correct measurement would no longer be guaranteed.
Instantly under application conditions
After cleaning, all elements of the diaphragm seal system were first fully welded into a single unit as usual, accompanied by the filling and adjustment of the system. Before delivery, however, there is another crucial step ? in its laboratory, WIKA simulated a vacuum 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 process suitability of the measuring system.
Note
Further information on the WIKA diaphragm seal systems are available on the WIKA website. Should Stressed have any questions, your contact will gladly help you.
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How do diaphragm seals work?
Watch the next video for more information concerning the functionality, application areas and advantages of diaphragm seals: