Pressure Drop across Control Valves

Let’s end this short week for the United States of America’s 4th of July Independence Day holiday with an educational video from Emerson’s Fisher Valves & Instruments YouTube channel.

The video, Control Valve Sizing Basics: What is Pressure Drop?, describes what this is, how to calculate it, and its importance in the selection of the right control valve for your application.

Pressure drop, or pressure loss, is the difference in pressure as measured between two points in a pipe with flowing fluid. Specific to control valves, it is the difference between the inlet pressure and outlet pressure. This pressure differential or Delta P is the inlet minus the outlet pressure. The unit of measurement is typically pounds per square inch differential (psid).

The standard is to measure the inlet pressure two pipe diameters upstream of the control valve and six diameters downstream. Control valve flow is a function of both the pressure drop across the valve and the valve travel.

In control valve selection, pressure drop plays a role in determining not only the valve and trim style, but the materials of construction as well. Higher pressure drops generally require highly engineered control valves for good performance.

For Fisher control valves, you can find the pressure drop information in the product bulletins. For example, the Fisher GX Control Valve and Actuator System page has links to several product bulletins including the Fisher Sliding-Stem Valve Selection Guide.

Visit the Control Valves section on for more on control valve selection and sizing. You can also connect and interact with valve experts in the Valves, Actuators & Regulators group in Emerson Exchange 365 and at the September 23-27 Emerson Exchange conference in Nashville.

Posted Wednesday, July 3rd, 2019 under Valves, Actuators & Regulators.

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