Featured Video: Tech Review: Liquid Flow Velocity

Knowledge of flow velocity, volumetric flow rate, and pipe diameter can assist operators in selecting, installing, and troubleshooting flow meters. This week’s featured video will guide operators in the math used to calculate flow velocity using volumetric flow and or pipe diameter.

Brent Baird with Instruments Direct demonstrates three techniques that will estimate flow velocity. The old school method utilizes a flow calculator slider ruler. With Brent’s particular ruler, by sliding to the known value for the inside pipe diameter (ID) in inches, the velocity in feet per second (FPS) can be read above the known value for volumetric flow in millions of gallons per day (MGD). Alternatively, the inside pipe diameter can be estimated by lining up the known values for velocity and volumetric flow and then looking at the value indicated under pipe diameter. Brent demonstrates that a cross reference chart performs the same calculations using a different visual.

Both of these tools are based off the equation GPM=2.45*ID²*FPS. If neither of his reference tools are available, plugging in the known FPS value for velocity and the inside pipe diameter in inches will calculate the volumetric flow rate. By rearranging the equation to solve for FPS, the flow velocity can be calculated using FPS=GPM/(2.45*ID²). Remember to follow PEMDAS. To calculate the internal pipe diameter with known values for FPS and GPM, rearrange the equation to solve for pipe diameter: ID= √(GPM/FPS/2.45). If the value for the internal pipe diameter is unknown, Brent demonstrates how an ANSI chart can be used to find that value.

With the video's final explanation of basic flow meter requirements, these calculations can be used to spot and avoid problem areas for flow metering in your distribution system.