LOW-HEAD BUBBLER IRRIGATION SYSTEMS .2. 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 l ow as one meter (3.3 ft). Air locks in bubbler systems can partially o r entirely block the flow of water, and thereby significantly decrease the uniformity of water application. To develop design criteria to pr event air locks from occurring in the delivery hoses, hydraulic labora tory experiments were conducted in the laboratory for smooth plastic h oses with internal diameters of 6, 8, 10, and 13 mm (1/4, 5/16, 3/8, a nd 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 e xcessive friction losses and poor water distribution uniformity, respe ctively. 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 flow s 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 th an 2 meters (6.6 ft), the 6 mm (1/4 in) diameter hose is recommended w ith design hows and velocities greater than 0.5 1/min (0.15 US gal/min ) and 0.29 m/s (1.0 ft s(-1)), respectively.