Energy Dissipation in Low Pressure Irrigation Pipelines: II Orifices

E rSION caused by water discharged from gated ipe openings can be reduced by dissipating excess energy with orifices placed in the gated pipe couplings. Laboratory tests were conducted to determine graphical relationships and coefficients for estimating the head loss for orifices made from galvanized sheet metal. The loss coefficient, K0, is a function of the orifice-to-pipe diameter ratio, 130, and can be expressed by an equation of the form K. = af31; where a and b are empirical constants determined from the tests. Comparisons made between machined, square edge orifices commonly used for flow measurement, and those made in sheet metal shops for irrigation showed that the irrigation orifices have a higher discharge coefficient and a lower head loss coefficient than do the square edge orifices. Square edge orifices placed in irrigation pipe couplings behaved similarly to those for flow measurement, particularly in the mid and lower ranges of the diameter ratio, 130. The head loss ratio, R, as defined by the ASME (1959) is the same for, (a) square edge orifices used for flow measurement, (b) square edge orifices installed in aluminum irrigation pipeline joint couplings, and (c) sheet metal orifices made for irrigation installed in pipe couplings. The ratio can be represented by the equation R=1-0.9 po i 7