The Open Pipe Flow Measurement Method
Over the years our team has been involved in countless pump start ups, many of which were field applications where instrumentation was non existent.
There is always an expectation of a specific flow rate or at least a minimum flow rate. Without a flow meter, how do you know if your pump is performing with flow rates that meet or exceed expectations?
Well fear not! Velocity and gravity to the rescue. As long as you have a discharge pipe which is horizontal and dumping into a tank or a pond that is accessible, physics can provide a method of estimating flow.
Known as the “pipe discharge drop method” or “the open pipe flow measurement method” it uses the trajectory of the fluid stream to determine fluid velocity and then applies the cross section area of the pipe to determine a flow rate.
Making measurements in inches and using the following formula below, a flow rate in USgpm can be approximated.
If a calculator is not handy, the table below also works.
For those of you that are lucky enough to be part of the generation that has never had to work with inches and feet, you will find below the metric version of the same formula. (Sorry, no table included)
Making measurements in meters and using the following formula, a flow rate in M3/min can be approximated.
So, the next time a customer or your boss asks, “ is it pumping as expected” you will, hopefully, be able to use the info I have passed on today to allow you to provide a quantifiable response.