HYDRAULIC DESIGN PROCEDURE FOR BYPASS FLOW METERS USING A PIPE BEND

Abstract

In agricultural machines and facilities, lowcost equipment and low energy consumption are necessary to reduceproduction costs. Pipe bends are very common in drip and sprinkler irrigation systems. When water passes through a pipebend, the water pressure at the outside radius of the bend is higher than that at the inside due to the centrifugal force of theflowing water. If the inside and outside radii of the pipe are connected by a pipe, a bypass flow is generated in this route. Fora given pipe bend and hydraulic resistance of the bypass route, the ratio (q/Q) of the bypass flow discharge (q) and the mainpipe flow discharge (Q) is a constant coefficient. Thus, a pipe bend with a bypass route can be used as a flow meter to predictthe flow rate and total discharge of the main pipe based on the measured bypass flow discharge and total amount of bypassflow water. In addition, the ratio q/Q changes with regulation of the hydraulic resistance of the bypass route, so the designedvalue of q/Q can be obtained by inserting a differentsize orifice into the bypass route. Based on results of hydraulicexperiments, a hydraulic design procedure for a bypass flow meter using a pipe bend is proposed. Since the bypass flowdischarge is very small in comparison with the main pipe flow discharge, the bypass route can use a smaller, less expensivemeter to accurately measure the main pipe flow discharge and the total amount of irrigation water. The cost becomes extremelylow when domestic water meters are used to measure the bypass flow because they are mass produced and relativelyinexpensive.