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8)0 CHAPTER 75 1962 Guide And Data Boole termination of the design rate of fiats in any particular sec tion of piping. The next general step is to determine the site of piping. As water flows through a pipe, the pressure continually de creases along the pipe, due to loss of energy from friction. The problem is then one of ascertaining the minimum pres sure in the street main, and the minimum pressure required for the operation of the topmost fixture. (A pressure of 15 psig may be ample for most flush valves, but reference should be made to the manufacturers' requirements. Some fixtures, especially wall-hung closets, require a pressure up to 25 psig. A minimum of 8 prig should be allowed for other fixtures.) The pressure differential thus obtained will be available for overcoming pressure losses in the distributing system, and in overcoming 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 high est fixture, may be obtained by multiplying the differences elevation in feet by the conversion factor 0.434. When water flows through a pipe, friction occurs as the re sult of the sliding of water particles past one another. If the pipe wall is rough, the roughness projections cause addi tional friction, owing to the development of increased turbu lence in the flowing water. As the water flows along a uni form pipe, the pressure decreases as a result of a dissipation of 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 is proportional to the length of Table 2 .... Demand Weights of Fixtures cn Fixture Units* fixture r Group* Typo of Supply Control Weight io Fixture IMh* 8tall or wall urinal........ Public......... Flush tank.. 3 Kitchen sink................... Hotel or restaurant .. Faucet......... Water closet................... Private.... Water closet................... 3 4 6 3 Shower head................... Private.... Mixing valve Bathroom group........... Private.... Flush valve Bathroom group........... Private.... Flush ~taok Separate shower........... Private .... Mixing valve Laundry trays (1-3)___ Private.... Faucet......... Combination fixture___ Private.... Faucet......... 2 8 6 2 3 3 From KBS Report BUSTS Wale-BfUemi / ButUixya. * Fot rapplr outlet* likely to irapreo eootinoow demands, eetimata contino- eoppty eepetately end add to total demand for fixture*. * Fw fixturca not tided, weights may be ssiumtd by comparing the fixture to a listed one nring water in quantities aod at ntre. * The given weights are for total ^tnand. For fixture* with W). hot aod mH water tURpfics, the weights for maximum separate Uy be taken as H the lieted demand for the supply. FIXTURE UNITS No. | for ifdsa predominantly for flush rulun. No. 2 for system predominantly for flush tanks. Fig. I... .Estimate Curves for Demand Load straight uniform pipes, and varies greatly with flow velocity pipe diameter, and roughness of pipe. Temperature has only a minor effect, within the working range, and usually is not considered. 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, brass, or lead may usually be as smooth. Fairly Rough. All ordinary pipes, such as wrought iron, gal vanised iron, steel, and cast iron, after a few years of usage, may be called fairly rough. Rough. Pipes that have deteriorated fairly rapidly for some 10 or 15 years after being laid, are classified as rough. Figs. 3, 4, and 5 give the pipe friction losses corresponding to these three types of pipes for various nominal diameters for a water temperature of 50 F.` Example I will illustrate the use of the charts. Example 1: A 214-in. fairly rough pipe supplies 100 gpm of water. Find the friction loss in head if the pipe length is 200 ft. Solution: Enter Fig. 4 at 100 gpm, and move along this line until it intersects the 214-in. diameter line. From thin intersec tion point, move vertically down and read 4j> psi friction loss per 100 ft of pipe length. Then the total friction loss will be 2 X 45 = 9 psi. The pressure losses in the distributing system will consist of the pressure losses in the piping itself, plus the pressure losses in the pipe fittings, valves, and the water meter, if any. Approximate design pressure losses for disc-type meters for various rates of flow are given in Fig. 6. Flow limits for disc- Fig. 2.... Section of Fig. 1 on Enlarged Scale Services FRICTION LOSS IN HEAD IN LBS. PER SQ. IN. PER 100 FT. LENGTH 811 FLOW IN G ALLO N S PER M IN U TE A,W ,,p. ol .ubi. bbow, *. Type TP. no. twipy =W-ly. Type TP bb b- U. *=" bTM= pip. Itb b. mbpcWd with bn* pip. a. b_ pip* ""> Typ. B iota- TM N.y,-ii.tL-. ny b. mibi, p-i F IriOio. k~ to Tn TP B ipbto-lb. Pi P* U far U, dual made dkceeter ot the tubin*. Fig. 3.... Flow Chart for Copper Tube1--