Document mp7GvvZj8XgMM95wKrE8rQ1pk

1200 CHAPTER 49 1958 -Guide FRICTION LOSS IN HEAD IN LBS. PER SQ. IN PER 100 FT. LENGTH Water Services FRICTION LOSS IN HEAD IN LBS. PER SO. IN. PER 100 FT. LENGTH 1201 Fig. 3. Flow Chart for Copper Tubing pressure required for the operation of the topmost fixture. (A pressure of 15 psi is ample for flush valves, but reference should be made to the manufacturers' requirements. A minimum of 8 psi should be allowed for other fixtures.) The pressure differential thus obtained will be available for overcoming pressure losses in the distributing system, and in over coming the difference in elevation between the water main and the highest fixture. The pressure loss, in pounds per square inch, caused by the difference in elevation between the street main and the highest fixture, may be ob tained by multiplying the difference in elevation in feet by the conversion factor 0.43. When water flows through a pipe, friction occurs as the result of the sliding of water particles past one another. If the pipe wall is rough; the roughness projections cause additional friction, owing to the develop ment of increased turbulence in the flowing water. As the water flows ^long a uniform pipe, the pressure decreases as a result of a dissipation of FRICTION LOSS IN HEAD IN LBS. PER SQ. IN. PER IOO FT. LENGTH Fig. 4. Flow Chart for Fairly Rough Pipe energy arising from the internal friction set up by viscosity of the water. This loss in energy is shown by the loss of pressure. The pressure loss proportional to the length of straight uniform pipes, and varies greatly with flow velocity, pipe diameter, roughness of pipe, and water tempera ture. On the basis of inside surface conditions, pipes may be classified- as smooth, fairly rough and rough, as follows: Smooth. The pipe surface shows no perceptible roughness. Pipes made of copper, rass, or lead may usually be classified as smooth. anifatr^ Rough. All ordinary pipes, such as wrought iron, galvanized iron, steel o cast-iron, after a few years of usage, may be called fairly rough. ifonoA Pipes that have deteriorated fairly rapidly for some 10 or 15 years after Deing laid, are classified as rough. Kgs. 3, 4 and 5 give the pipe friction losses corresponding to these three of pipes for various nominal diameters for a water temperature of - * Example 1 will illustrate the use of the charts.