Flow Control Emitters – Optimizing Both Flexibility and Uniformity

Abstract

Abstract.Drip irrigation emitters are categorized by their flow exponents which describe their ability to regulate flow in relation to pressure. Emitters with flow exponents near 1.0 to 0.8 use small flow paths such as microtubes and experience laminar flow; emitters with flow exponents near 0.4 - 0.6 use orifice flow, tortuous-path or vortex flow and experience turbulent flow; and emitters with flow exponents less than 0.2 are considered pressure compensating (after Boswell, 1990). There are advantages and disadvantages within each of these emitter categories in relation to flexibility in adjusting overall flow in an irrigation block, and achieving high flow uniformity between emitters in a block, which is often expressed as distribution uniformity (DU) or emission uniformity (EU). Having the flexibility to adjust the overall flow in an irrigation block is valuable to accommodate ever changing weather conditions and/or farm irrigation logistics. For example, higher than normal crop water use as a result of elevated temperature events may be accommodated more quickly by raising the system inlet pressure, rather than increasing system run time. In contrast, lowering the system application rate by lowering the system inlet pressure is often a convenient method to accommodate lower than normal crop water use periods rather than reducing the run time and disrupting the irrigation schedule. Achieving high DU and/or EU is always desirable in order to maximize resource use efficiency, crop yield and crop quality. Emitters with high exponent values (near 1.0) provide high flexibility in adjusting overall flowrate versus pressure, but deliver poor distribution uniformity as pressure varies within a block. Emitters with low exponent values (near 0) have little flexibility in adjusting overall flowrate versus pressure, but deliver uniform flow between emitters in a block across a wide operating pressure range. Turbulent flow emitters (with exponent values near 0.5) offer moderate flexibility in adjusting overall flowrate versus pressure, and moderate flow uniformity between block emitters. To optimize both flexibility and uniformity, Aqua-Traxx FC Flow Control premium drip tape (ATFC) incorporates an emitter with a flow exponent 0.3 (Aqua-Traxx FC, 2014). Since this emitter is unique, it is proposed that all emitters with a flow exponent near 0.3 be described as ‘flow control‘ emitters. This paper will describe the end-user benefits of using flow control emitters, including improved flexibility to adjust application rates compared to pressure compensating emitters with a flow exponent of 0.1, and better distribution uniformity between emitters in a block compared to a tape using turbulent flow emitters with an exponent of 0.5. These benefits may be summarized as control (over application rates) without compromise (of distribution uniformity).