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Under Pressure, Part 6: Size Matters with Flowmeters and Pressure Regulators

Oct 04, 2012

In this final post on pressure regulation and flow meters, I’d like to present a case study. A customer was convinced that our unit intermittently lost control for given flow rates. It turns out that as they increased flow rate, the outlet pressure of the regulator (inlet to the mass flow controller) was drooping below the allowable flowmeter inlet pressure, and thus, the MFC would lose control.

If the flow rate was lowered or the regulator was adjusted to add pressure back to the inlet, the flowmeter would again control correctly. But without paying attention to the “droop” or doing something to counteract the inherent problem it caused, it was causing massive throughput issues that were incorrectly placed on the MFC. Once the regulators were sized more appropriately, the problem disappeared completely.

Flow meter sizing is very important, but so is sizing your plumbing and other flow-related devices, particularly those that directly affect the operation of your MFC.Flowmeters and Droop: a case study

Learn more about the relationship between flowmeters and pressure regulators by reading my previous posts on seat-drop lock, avoiding droop (hysteresis), droop and choked flow and pressure drop. As always, we are happy to help you with applications relating to gas mass flow control in your system. Contact us for more information.


Morgan Zealear, Engineer
Written By:
Morgan Zealear, Engineer
Sierra Instruments

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