In this study, physical models were designed and fabricated to investigate the hydraulic behaviour of dead-end and looped PVC manifolds. The physical models consisted of a water supply tank with overflow, PVC manifolds, steel supports, collection tank, pump, pressure sensors and valves to allow flow control. Throughout the study, the water level in the supply tank was kept constant. The hydraulic behaviour of dead-end manifolds was investigated using different spacing, S between outlets (S= 3m, S=2.5m, S=2m, S=1.5m, and S=0.75m). The hydraulic behaviour of looped manifolds was investigated using a single outlet spacing of 1.5m. The comparison between the hydraulic behaviour of looped and dead-end manifolds was carried out using the data of the 1.5m outlet spacing. The value of uniformity, U for dead-end and looped manifolds was 82% and 92%, respectively. The value of friction ratio, fn/f1, was found to be 33 and 0.18 for dead-end and looped manifolds, respectively. The experimental data of this study were used to validate selected formulae for estimation of the friction correction factor (G Factor). The results showed that the equation proposed by Alazba et al. (2012) yielded the most satisfactory estimation. The performance of the selected formulae was tested using two statistical indices.

• Alawee, W. H., Almolhem, Y. A., Yusuf, B., Mohammad, T. A., & Dhahad, H. A. (2020). Variation of coeffcient of friction and friction head losses along a pipe with multiple outlets. Water, 12(844), 1-15. https://doi.org/10.3390/w12030844

• Alawee, W. H., Hassan, J. M., & Mohammad, W. S. (2016). Experimental and numerical study on the improvement of uniformity flow in a parallel flow channel. Engineering and Technology Journal, 34(5), 847-856.

• Alawee, W. H., Yusuf, B., Mohammad, T. A., & Dhahad, H. A. (2019). Variation of flow along a multiple outlets pipe with various spacing and inflow water head based on physical model. Journal of Engineering Science and Technology, 14(4), 2399-2409.

• Alazba, A. A., Mattar, M. A., El-Nesr, M. N., & Amin, M. T. (2012). Field assessment of friction head loss and friction correction factor equations. Journal of Irrigation and Drainage Engineering, ASCE, 138(2), 166-176. https://doi.org/10.1061/(ASCE)IR.1943-4774.0000387

• Albertson, M. L., Bartion, J. R., & Simons, D. B. (1960). Fluid Mechanics for Engineers. Prentice Hall.

• Anwar, A. A. (1999). Factor G for pipeline with equally spaced multiple outlets and outflow. Journal of Irrigation and Drainage Engineering, ASCE, 125(1), 34-38. https://doi.org/10.1061/(ASCE)0733-9437(1999)125:1(34)

• Christiansen, J. (1942). Irrigation by sprinkling. University of California, Agricultural Experiment Station Bulletin.

• Gandhi, M. S., Ganguli, A. A., Joshi, J. B., & Vijayan, P. K. (2012). CFD simulation for steam distribution in header and tube assemblies. Chemical Engineering Research and Design, 90(4), 487-506. https://doi.org/10.1016/j.cherd.2011.08.019

• Hassan, J. M., Mohamed, T. A., Mohammed, W. S., & Alawee, W. H. (2014a). Modeling the uniformity of manifold with various configurations. Journal of Fluids, 2014, Article 325259. https://doi.org/10.1155/2014/325259

• Hassan, J. M., Mohammed, W. S., Mohamed, T. A., & Alawee, W. H. (2014b). Review on single-phase fluid flow distribution in manifold. International Journal of Science and Research, 3(1), 325-330.

• Hassan, J. M., Mohammed, W. S., Mohamed, T. A., & Alawee, W. H. (2014c). CFD simulation for manifold with tapered longitudinal section. International Journal of Emerging Technology and Advanced Engineering, 4(2), 28-35.

• Hassan, J. M., Mohamed, T. A., Mohammed, W. S., & Alawee, W. H. (2015). Experimental and numerical study on the improvement of uniformity flow for three-lateral dividing manifold. International Journal of Engineering and Technology, 12(1), 29-37.

• Howland, W. E. (1935). Gain in head at take-offs. Journal of the New England Water Works Association, 49(1), Article 14.

• Keller, J., & Bliesner, R. D. (1990). Sprinkle and trickle irrigation. Springer Science + Business Media.

• Koh, J. H., Seo, H. K., Lee, C. G., Yoo, Y. S., & Lim, H. C. (2003). Pressure and flow distribution in internal gas manifolds of a fuel-cell stack. Journal of Power Sources, 115(1), 54-65. https://doi.org/10.1016/S0378-7753(02)00615-8

• Legates, D. R., & McCabe, J. (1999). Evaluating the use of “goodness-of fit” measures in hydrologic and hydroclimatic model validation. Water Resources Research, 35(1), 233-241. https://doi.org/10.1029/1998WR900018

• Maharudrayya, S., Jayanti, S., & Deshpande, A. P. (2005). Flow distribution and pressure drop in parallel-channel configurations of planar fuel cells. Journal of Power Sources, 144, 94-106. https://doi.org/10.1016/j.jpowsour.2004.12.018

• Mohammed, T. A., Noor, M. J. M. M., Halim, A. G., Badronnisa, Y., Soom, M. A. M., & Benzagta, M. A. M. (2003). Experimental study on the friction loss and uniformity of lateral discharge along a manifold. Journal of Institution of Engineers Malaysia, 64(2), 20-25.

• Mokhtari, S., Kudriavtsev, V. V., & Danna, M. (1997). Flow uniformity and pressure variation in multi-outlet flow distribution pipes. Advances in Analytical, Experimental and Computational Technologies in Fluids, Structures, Transients and Natural Hazards, 355, 113-122.

• Mostafa, E. A. (2004, March 26-28). Correction factor for friction head loss through lateral and manifold. In Eighth International Water Technology Conference IWTC8 (pp. 735-749). Alexandria, Egypt.

• Oron, G., & Walker, W. (1981). Optimal design and operation of permanent irrigation systems. Water Resources Research, 17(1), 11-17. https://doi.org/10.1029/WR017i001p00011

• Provenzano, G., & Pumo, D. (2004). Experimental analysis of local pressure losses for microirrigation laterals. Journal of Irrigation and Drainage Engineering, 130, 318-324. https://doi.org/10.1061/(ASCE)0733-9437(2004)130:4(318)

• Sadeghi, S. H., & Peters, T. (2011). Modified G and Gavg correction factors for laterals with multiple outlets and outflow. Journal of Irrigation and Drainage Engineering, ASCE, 137(11), 697-704. https://doi.org/10.1061/(ASCE)IR.1943-4774.0000332

• Streeter, V. L., Wylie, E. B., & Bedford, K. W. (1998). Fluid mechanics (9th Ed.). McGraw-Hill Publishing Company.

• Tong, J. C. K., Sparrow, E. M., & Abraham, J. P. (2009). Geometric strategies for attainment of identical outflows through all of the exit ports of a distribution manifold in a manifold system. Applied Thermal Engineering, 29(17-18), 3552-3560. https://doi.org/10.1016/j.applthermaleng.2009.06.010

• Valiantzas, J. (2002). Continuous outflow variation along irrigation laterals: Effect of the number of outlets. Journal of Irrigation and Drainage Engineering, ASCE, 128, 34-42. https://doi.org/10.1061/(ASCE)0733-9437(2002)128:1(34)

• Vallesquino, P., & Luque-Escamilla, P. L. (2002). Equivalent friction factor method for hydraulic calculation in irrigation laterals. Journal of Irrigation and Drainage Engineering, 128(5), 278-286. https://doi.org/10.1061/(ASCE)0733-9437(2002)128:5(278)

• Yildirim, G. (2007). Analytical relationship for designing multiple outlets pipelines. Journal of Irrigation and Drainage Engineering, ASCE, 133(2), 140-154. https://doi.org/10.1061/(ASCE)0733-9437(2007)133:2(140)