A diaphragm seal system in vacuum pressure process must master a significant challenge ? it must deliver a trusted measuring result, even when the pressure drops and the temperature rises simultaneously. The example of a chemical company producing phthalic anhydride (PA) shows 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, 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 procedure temperature can rise to more than 230 �C as the pressure drops to 100 mbar abs. With such a 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 obtain a measuring solution that could also fulfil its task with the required accuracy in the long run 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 elements of this measuring system were selected specifically 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 connection 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. Due to this fact, correct measurement would no more 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, followed by the filling and adjustment of the system. Before delivery, however, there was another crucial step ? in its laboratory, WIKA simulated a vacuum process for the diaphragm seal system relative to the client?s conditions and subjected it to a thermal ageing process. This test confirmed the procedure suitability of the measuring system.
Note
More info on the WIKA diaphragm seal systems are available on the WIKA website. Assuming you have any questions, your contact will gladly help you.
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How do diaphragm seals work?
Watch the next video to learn more concerning the functionality, application areas and advantages of diaphragm seals:g