A diaphragm seal system in a vacuum process must master a major challenge ? it must deliver a trusted measuring result, even though 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 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 process, 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 beyond your 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 term under the conditions described. WIKA then drew on pressure gauge octa -depth expertise to create 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 specifically for the application. Silicone oil KN32 was therefore selected as the fill fluid for pressure transmission. The cleaning and conditioning of the diaphragm seal, the capillary, the connection 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, accompanied by the filling and adjustment of the machine. Before delivery, however, there was 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. When you have any questions, your contact will gladly assist you to.
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Just how do diaphragm seals work?
Watch the next video to learn more concerning the functionality, application areas and advantages of diaphragm seals: