A remote seal differential pressure transmitter may perform perfectly under positive pressure—but vacuum applications are a completely different challenge.
The difference isn’t just the pressure range. It lies inside the remote seal system.
When process pressure drops below atmospheric pressure, the fill fluid inside the capillaries and diaphragm seals is subjected to much lower absolute pressure. If the fill fluid is not specifically designed for vacuum service, dissolved gases can come out of solution and form microscopic bubbles.
These tiny bubbles may seem insignificant, but they can lead to:
• Zero drift
• Slow response time
• Reduced measurement accuracy
• Long-term instability after repeated vacuum cycles
That’s why vacuum applications often require vacuum-grade silicone oil with lower vapor pressure and superior degassing characteristics.
But selecting the right fill fluid is only part of the solution.
Before shipment, transmitters intended for vacuum service should also undergo dedicated vacuum processing. This removes residual air and dissolved gases from the fill system, ensuring the capillaries and diaphragm seals remain completely filled and stable when exposed to negative pressure.
A well-designed remote seal system for vacuum applications combines:
✔ Vacuum-grade silicone fill fluid
✔ Thorough vacuum filling and degassing process
✔ Optimized diaphragm seal design
✔ Stable performance throughout repeated vacuum cycles
In remote seal differential pressure transmitters, what happens inside the capillary is just as important as what happens inside the process.
A transmitter designed for positive pressure is not automatically suitable for vacuum service. Proper fill fluid selection and manufacturing processes make the difference between stable long-term performance and persistent measurement drift.
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