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WaterOperator.org Blog

Articles in support of small community water and wastewater operators.

Featured Video: Tech Review: Liquid Flow Velocity

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.

Featured Video: Flow Meters for Water and Wastewater Applications

Featured Video: Flow Meters for Water and Wastewater Applications

With the wide variety of flow meters available these days, problems with flow measurement can sometimes be traced back to having the wrong technology for the job. It is important, then, for those who have their feet on the ground at the plant to know the options available. 

You’ll need to consider: is closed pipe or open channel the right solution?  What is the right technology to use once I have decided on open or closed pipe? What are the total maintenance costs involved with each of the decisions? This 43-minute video presents typical water and wastewater applications and flow meter solutions. It reviews theory of operations and application details to help you select the correct flow meter technology. Because, as they say, in order to manage it, you have to measure it!