Document k6Be889Z04wLRm8axRRqqnQOy

766 CHAPTER 56 1960 Guide termination of the design rate of flow in any particular sec tion of piping. The next general step is to determine the size of piping. As water flows through a pipe, the presure 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 IS 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 psig 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 difference in 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 tions! friction, owing to the development of increased turbulence 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 Toble'2 .... Oemond Weights of Fixtures in Fixture Units* fixture or Groupb Occupancy Type of Supply - Confrol Woight in fixture Units* Stall or wall urinal........ Public......... Flush valve. Stall ox wall urinal........ Public.......... Flush tank.. 5 3 Lavatory...................... Public.......... Faucet.......... ' -.2 Kitchen sink.................... Hotel or restaurant .. Faucet.......... Water closet.................... Private .: .. Flush valve . Water closet.................... Private.... Flush tank.. 4 6 3 Shower head.................... Private .... Mixing valve 2 Bathroom group............ Bathroom group............ Separate shower............ Private .... Private... Private........ Flush valve for closet.'. Flush tank for closet.. Mixing valve 8 6 2 Laundry trays (1-3)___ Private........ Faucet.......... . 3 Combination fixture___ Private.... Faucet.......... 3' From KBS Beport BHS79 WaUr-DittrUnUis^ Sptinat far StnUtn#*. Forsopply outlets likely to impose continuous demand*, estimate eontinu- oesenpply separately and odd to total <fem*(td for fixture. b For fixtures not listed, vteigbts may be amumed by comparing the fixture to a listed one using wnta in shailar quantities and at similar rates. ' * The peon weights are for total demand. For fixtures with both bot and cold water supplies, the weights for maximum separate demands may be taken as K the listed demand for the supply. No. I for ryjfnm predominantly for Audi voire*. No. 2 for system predominantly for flujfc tanks. Rg. 1... .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 classified 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 Borne 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.1 Example' 1 will illustrate the use of the charts. Example /. 'A 2Vi-m. 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 2)4-in. diameter line. From this intersec tion point, move vertically down and read 45 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 disctype meters, which may be regarded as the limits of recom- Woter Services FRICTION LOSS IN HEAD IN LBS. PER SQ. IN. PER IOO FT. LENGTH * Aoother type of copper tubing, known as Type TP, now a being used extensively. Type TP tubing baa tbe one outside diameter aa standard bras* pipe It be interchanged with bnae pipe Or connected to bxaat pipe, using silver solder. Type B tubing, made to US Navy may be similarly uaed. Per friction Ion in Type TP or Type B tubing, tbe designer should adjust values of Fig. U for the actual inside diameter of tbe tubing. Fig. 3.... Flow Chart for Copper Tube1-* FLOW IN GALLONS PER M INUTE