Under Pressure, Part 5: Flowmeters on the Ragged Edge of Pressure Drop

Think about it. It’s pretty much impossible to make a controlled pressure drop without burning up some energy as heat. Therefore, the outlet pressure and flow rate cannot be linearly proportional at 1:1, but rather, must have some positive loss of X:1, where X is greater than 1.

So, for a given regulator setpoint, the outlet pressure will vary with flow rate. Conversely, the flow rate will vary as the setpoint outlet pressure is changed. And that means that if you are changing flow rate with regularity, then your pressure regulator must also change physical ride height to maintain a given outlet pressure. Otherwise, the outlet pressure of the regulator will vary with flow rate, likely affecting accuracy or operability. This is particularly true if the current conditions have your flow meter running on the ragged edge of pressure drop energy necessary for steady control.

Have additional questions about pressure regulators, undersizing, seat-drop lock or droop? I’ve talked about these conditions in this ongoing series about pressure regulation and flowmeters. But you can also contact us for more information about the gas mass flow control in your system.