Pitot Testing for Large Flow Meters in Water Supply

M.E. Simpson Co., Inc. employs the use of a Polcon® Pitot Rod to accurately measure velocity of water flowing in a pipe, thereby determining the accuracy of a flow meter at a single flow or over a broad range of flows.  This equipment can be used to monitor flows for testing meters up to 108 inches. This procedure consists of placing an insertion pitot tube into the pipe and measuring the velocity at equidistant points over the cross section. From this, a velocity profile is generated and used to determine the average velocity through the pipe, and then the flow-rate through the pipe.

The Polcon® Pitot Rod measures the differential pressure between the averaged velocity head port and the averaged static head port. The fluid velocity is proportional to the square root of the differential pressure. This differential pressure is measured and recorded over time by the Polcon® Sentry digital manometer and data recorder. The results are then compared to the readings from the flow meter being tested for the same time period and accuracy is then calculated for the flow meter. According to the AWWA M33 Manual, “Flow Meters in Water Supply” pitot testing can produce results of + 1/2 % to 5% of full scale with a “Repeatability” of 0.5 %. Using the Polcon® Sentry Recorder which registers differential pressure to one one-hundredth of an inch of water column, this accuracy can be improved to the + 1/2% to + 2% range. Repeatability remains the same due to test site conditions as long as the test site conditions are within the specifications for producing un-obstructed flow.