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Hydraulic Friction

Hydraulic Friction means the friction of water against water as contrasted with the friction of solid against solid. There are important points of difference in the two cases. Hydraulic friction is independent of the pressure; there is no more waste of energy in a foot-length of a water-main at one level than there is in an equal length of the same main at a higher level, and, therefore, lower pressure. This constitutes an important reason why force-pumps with great lifts may be made more efficient than those with small lifts, the former not requiring a proportionate amount of power to overcome the fluid friction in the pump and pipes. On the other hand, hydraulic friction is proportional to the speed for slow rates of motion, increasing with more than proportionate rapidity as the rate increases. [Friction, Hydraulics.]