Hydraulic Design Procedure for Bypass Flow Meters Using a Pipe Bend

In agricultural machines and facilities, low–cost equipment and low energy consumption are necessary to reduce production costs. Pipe bends are very common in drip and sprinkler irrigation systems. When water passes through a pipe bend, the water pressure at the outside radius of the bend is higher than that at the inside due to the centrifugal force of the flowing water. If the inside and outside radii of the pipe are connected by a pipe, a bypass flow is generated in this route. For a given pipe bend and hydraulic resistance of the bypass route, the ratio (q/Q) of the bypass flow discharge (q) and the main pipe flow discharge (Q) is a constant coefficient. Thus, a pipe bend with a bypass route can be used as a flow meter to predict the flow rate and total discharge of the main pipe based on the measured bypass flow discharge and total amount of bypass flow water. In addition, the ratio q/Q changes with regulation of the hydraulic resistance of the bypass route, so the designed value of q/Q can be obtained by inserting a different–size orifice into the bypass route. Based on results of hydraulic experiments, a hydraulic design procedure for a bypass flow meter using a pipe bend is proposed. Since the bypass flow discharge is very small in comparison with the main pipe flow discharge, the bypass route can use a smaller, less expensive meter to accurately measure the main pipe flow discharge and the total amount of irrigation water. The cost becomes extremely low when domestic water meters are used to measure the bypass flow because they are mass produced and relatively inexpensive.