Practical two-stage pipe expansions for centrifugal pump irrigation

Graduation date: 1990Centrifugal irrigation pumps discharge fluids at high velocities that must be slowed\ud to minimize energy losses due to friction. Pipe expansions make the transition to larger\ud pipes associated with slower velocities. Expansions convert the upstream velocity head\ud to static head in the downstream pipe. The transition to a larger pipe is commonly an\ud abrupt or single-stage conical pipe expansion. Two-stage conical pipe expansions have\ud been shown to be more efficient and a potential alternative.\ud Four two-stage pipe expansions using standardly available materials were\ud constructed and tested at common irrigation flow rates. These expansions require less\ud space and cost less than optimum two-stage expansions. Pressure change across the pipe\ud expansions were measured. The calculated head loss coefficients were compared to\ud published values of abrupt, single-stage, and optimum two-stage pipe expansions.\ud Head loss coefficients for the 50 - 100 mm and 75 - 150 mm two-stage expansions\ud averaged 0.32 and 0.28 respectively. Loss coefficients for the 100 - 200 mm and 125 -\ud 250 rim two-stage expansions averaged 0.16 and 0.17 respectively.\ud The two-stage expansions operated more efficiently than abrupt and single-stage\ud expansions and were economically practical for many pumping situations. The 50 - 100\ud mm two-stage expansion was only a slight improvement over a single-stage welding\ud cone expansion. The fitting was economical as electricity prices rose over $0.05/kWh\ud for crops requiring 3000 annual operating hours. The larger fittings became\ud progressively better. The 75 - 150 mm expansion became economically practical at\ud $0.03/kWh when operating more than 1,600 hours. The 100 - 200 mm and 125 - 250\ud mm two-stage fittings were always practical. Beginning with the 75 - 150 mm size and\ud increasingly with the next two larger sizes, optimum two-stage fittings became\ud economically competitive. Optimum two-stage expansions operated most efficiently,\ud but because of their high cost were only practical for high electricity costs and long\ud irrigation seasons.\ud The three largest two-stage expansions tested are improvements over abrupt or\ud single-stage expansions when constructing a pump discharge. Replacing an existing,\ud less efficient expansion may not be cost effective because the existing fitting cost is lost.\ud While only a small part of an irrigation system, these two-stage expansions can improve\ud system performance with little extra cost and without requiring difficult to obtain\ud components