Low-head bubbler irrigation systems. Part II. Air lock problems

Air locks may occur in pipelines of low-pressure, gravity-flow bubbler irrigation systems located on level fields and with design heads as low as one meter (3.3 ft). Air locks in bubbler systems can partially or entirely block the flow of water, and thereby significantly decrease the uniformity of water application. To develop design criteria to prevent air locks from occurring in the delivery hoses, hydraulic laboratory experiments were conducted in the laboratory for smooth plastic hoses with internal diameters of 6, 8, 10, and 13 mm ( 1 4, 5 16, 3 8, and 1 2 in). Hose diameters less than 6 mm ( 1 4 in) and greater than 10 mm ( 3 8 in) are not recommended for low-head bubbler systems due to excessive friction losses and poor water distribution uniformity, respectively. For bubbler systems with design heads less than 2 meters (6.6 ft), the 10 mm ( 3 8 in) diameter hose is recommended with design flows and velocities greater than 1.7 1/min (0.42 US gal/min) and 0.37 m/s (1.2 ft s^-1), respectively. For systems with design head greater than 2 meters (6.6 ft), the 6 mm ( 1 4 in) diameter hose is recommended with design flows and velocities greater than 0.5 1/min (0.15 US gal/min) and 0.29 m/s (1.0 ft s^-1), respectively.