Lecture 10 Minor Losses Pressure Requirements（讲座10小损失及压力要求）.pdf

Lecture 10 Minor Losses Pressure Requirements I. Minor Losses • Minor (or “fitting”, or “local”) hydraulic losses along pipes can often be estimated as a function of the velocity head of the water within the particular pipe section: 2 V hml Kr (208) 2g where hml is the minor loss (m or ft); V is the mean flow velocity, Q/A (m/s or 2 2 fps); g is the ratio of weight to mass (9.81 m/s or 32.2 ft/s ); and K is a r coefficient, dependent on the type of fitting (valve, bend, transition, constriction, etc.) • Minor losses include head losses through/past hydrants, couplers, valves, pipe elbows, “tees” and other fittings (see Tables 11.1 and 11.2) • For example, there is some loss when water flows through a hydrant, but also some loss when water flows in a pipe past the location of a closed hydrant • K = 0.3 to 0.6 for flow in a pipeline going past a closed hydrant, whereby the r velocity in the pipeline is used to compute hml • Kr = 0.4 to 0.8 for flow in a pipeline going past an open hydrant; again, the velocity in the pipeline is used to compute hml • Kr = 6.0 to 8.0 for flow from a pipeline through a completely open hydrant. In this case, compute hml using the velocity of the flow through the lateral fitting on the hydrant, not the flow in the source pipeline. • For flow through a partially open hydrant, Kr increases beyond