Minor losses in start connectors of microirrigation laterals

Fittings called start connectors are usually employed to attach each lateral to its corresponding manifold in microirrigation systems. The protrusion of start connectors’ barbs into the manifold induces pressure losses due to contraction and subsequent enlargement of streamlines. In addition, when water flows from a manifold toward a lateral through a start connector, a sudden contraction followed by expansions of flow streamlines cause pressure loss whose intensity is influenced by connector’s geometry. Minor losses along manifolds or at laterals inlet due to start connectors may be significant and might be considered on subunits design or while undertaking hydraulic simulations. The objectives of this research were: (a) to develop equations based on dimensional analysis to estimate minor losses due to start connectors; (b) to compare the accuracy of the developed models against models that are currently used for estimating minor losses; (c) to undertake simulations to assess the relevance of minor losses due to start connectors in hydraulics of subunits. Minor losses due to start connectors were separated into two components. A model was developed and validated to estimate minor losses due to the protrusion of start connectors inserted along a manifold. Two models were developed and validated to estimate minor losses that occur when water flows from a manifold into a lateral line through a start connector. The required data to develop and validate the models were obtained experimentally in laboratory. Although minor losses due to start connectors represented a relative small percentage of total head losses, such effects may be significant while undertaking rigorous hydraulic simulations that require accurate estimation of pressure losses.
The authors are grateful to the following Brazilian institutions for their financial support: the Federal Department of Science and Technology (MCT); the National Scientific and Technological Development Council (CNPq); the Sao Paulo State Scientific Foundation (FAPESP) and the National Institute of Science and Technology in Irrigation Engineering (INCTEI)