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 at the same time. The example of a chemical company producing phthalic anhydride (PA) shows that it is in no way self-evident that this requirement could be met on a consistent basis.
PA is primarily used as a plasticiser for plastics. However, additionally it is found in the production of synthetic resins and dyes. Inconsiderate 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 technique, the critical phase for pressure measurement occurs in the distillation column. There, the process temperature can rise to a lot more than 230 �C while the pressure drops to 100 mbar abs. With such a 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 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 company approached WIKA with the obtain a measuring solution that would also fulfil its task with the required 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 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 form. Silicone oil KN32 was therefore selected because the fill fluid for pressure transmission. No One Talks About 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 volume balance of the diaphragm seal system and therefore impair its function. Therefore, correct measurement would no more 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 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 for more information concerning the functionality, application areas and benefits of diaphragm seals: