Performance of Chemigation Backflow Prevention Assemblies

When chemicals are applied using irrigation systems, there is potential for contamination of the water source by backflow if the irrigation system shuts off while unattended. This study was conducted to determine the operating and performance characteristics of new, i.e., unused, chemigation backflow prevention assemblies (CBPAs). Four manufacturer's models were tested in the laboratory. However, two of CBPAs have been modified since the testing was completed. In general, the CBPAs do not meet the standards established for municipal water suppliers and many industries. The backpressures required for the two current models to seal were 0.0 and 6.7 kPa (1.0 psi). Backflow was a function of backpressure for the three check valves that did not seal at zero backpressure. All four valves exhibited a backpressure backflow relationship when artificially fouled with hexagonal bars placed across the valves seat. At the backpressure head of 3.7 m (12 ft), the low pressure drains on all models intercepted 100% of the backflow (leakage) when the check valves were fouled with 0.12 cm (3/64 in.) bars placed across the valves seats. A typical backpressure head after shutoff of a center pivot irrigation system is 3.7 m (12 ft). These findings support the results of field tests of eight used valves where the low pressure drains intercepted 100% of the backflow at all backpressure heads evaluated [3.7 m and less (12 ft)].