MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

154can quickly tire man and animal, causing loss of water lifting performance.In such conditions it may be advantageous to provide supplemental powersources. For example, when dust is a problem, the wind may be strong enoughto drive the water lifter via a windmill. As drivers using solar energybecome more available, they would seem the ideal power when the heat is toogreatfor man or animal.6.3 lVater RequirementsAfter the number of water lifters usable for a given application hasbeen reduced by availability and adaptability, possible water liftersmust then meet the water requirements for the situation. As discussed inSection 2.2, these are basically the discharge and total head, however theNPSHR and power needs should also be kept in minds ifapplicable.Throughout the preceding chapters, the Q and H ranges for variouswater lifters and pumps have been given, Figure 6.1 presents a guide tothe selection of positive displacement and rotodynamic pumps based ontypical H-Q ranges. The gray areas serve only as rough boundaries and donot represent absolute limits. Once such an examination of ranges (seealso Figure 4.8) has narrowed the field to a few types of pumps, manufacturer’scharts, should be consulted to find the optimum size and design.These charts are a performance composite of several pumps. Prom thisselection, the performance curve can be obtained and compared to the H-Qcurve of the pumping system (see Figure 2.1). The intersection of the systemand pump curves indicates the H and Q at which they will operate. Thispoint should also correspond to as near as possible the maximum efficiencyof the pump. If the pump is to operate over a range of discharges or heads,the efficiency curve should be as flat as possible throughout that range.