Document LgKKjvx9jpXoG4DOxexLejepw

984 CHAPTER 48 1950 Guide Table 3. Performance Requirements of Water Meters1 Size In. qu U4 R A Normal. Test-Flow Limits GPM 1 to 2 to 3 to 5 to 20 34 53 100 8 to 160 16 to 315 28 to 500 48 to 1,000 Minimum Test-Flow GPM H. v IJa 2 4 7 12. American Water Works Association Standards: ... , Registration. The registration on the meter dial shall indicate the quantity recorded^ to.be not less than 98 per cent nor more than 102 per cent oi the water actually passed through the meter while it is being tested at rates of flow within the specified limits herein under normal teet flow limits: There, shall be not less than 90 per cent of the actual flow recorded when a test is made at the rate of flow set forth under minimum test to 2.2 ft of straight 1 in. pipe. Therefore, for each 1 in., 90 deg elbow, 2.2 ft of 1 in. pipe are added to the total length of 1 in. pipe. Estimated pressure losses.for pipe fittings and valves in terms of equiva lent pipe length are shown in Table 4. Table 5 lists the equivalent lengths for various special types of ap paratus and fittings. The loss, in water meters varies considerably with the design even in meters of the same nominal size. The values given in Table 5 are ample for the well-known meters now on the market. Example S. Assume a minimum street main pressure of 55 psi; a height of topmost fixture above street main of 50 ft; a developed pipe length from water main to.highest fixture of 100 ft; a total load on the system of 50 fixture units; and that the.water closets are flush-valve operated. Find the required size of supply main. . Solution. From Fig. 2 the estimated peak demand is found to be 51 gpm. From Table 3 it is evident that several sizes of meters would adequately measure this flow. For a trial computation choose the 11 in. .meter. From Fig. 6 the .pressure drop through a,li in. disc-type meter for a flow of 51 gpm is found to be 6.5 psi. ' Then the pressure drop available for overcoming friction in pipes and fittings is 55 - (15 + 50 X 0.43 + 6.5) = 12 psi. At this point it is necessary to make some estimate of the equivalent pipe length of the fittings on the direct line from the street main to the highest fixture. The exact equivalent length of the various fittings cannot now be determined since the. Table 4. Allowance in Equivalent Length of Pipe fob Fbiction Loss in Valves and Thbeaded Fitungs x Diameter op Fitting In. H<1-- V*. 1 Ui- 1% 2' 2)i- a at$ Af~ a <L~,-- 90 Deg Standard Ell Ft Equivalent Length op Pipe for Various Fittings 45 Deg Standard Ell Ft 90 Deg Side Tee Ft \ Coupling or Straight Run of Tee Ft Gate Valve Ft Globe . Valve Ft i 2 2.5 3 4 5 7 8 10 12 14 - 17 20 0.6 1.2 1.5 1.8 2.4 3 4 5 6 7 8 10 12 1.5 3 4 5 6 7 10 12 15 18 21 25 30 0.3 0.6 0.8 0.9 1.2 1.5 2 - 2.5 3 3.6 4.0 5 6 0.2 8 0.4 15 0.5 20 0.6 25 0.8 35 1.0 45 1.3 . 55. 1;6 65 2 80 2.4 100 2.7 125 3.3 140 4 . .165 Angle Valve Ft 4 8 12 15 18 22 28 34 40 50 55 70 . 80 Water Services 985 Table 5. Equivalent Lengths of Ibon Pipe to Give Same Loss as Special Fittings and Apparatus Fitting Apparatus 30-eal Vertical hot-water tank, j in. pipe... 30-gal Horizontal hot-water tank, f in. pipe Water meters (No valves included) { in. with in. connections......................... } in. with | in. connections......................... f in. with f in. connections......................... 1 in. with 1 in. connections......................... 1$ in. with 1 in. connections........................................ Water softener................................................... Nominal Diameter of Pipe--Inches t1 4 17 1.2 5 1 56 16 11 _ -- 6.7 28 90 4.8' 20 64 ' 3.4 14 45 -- 9 30 -- 4.4 14 -- 50-200 -- -- ----- . -- 115 54 -- pipe sizes of the building main, riser, and branch leading to the highest fixture are not known as yet, but a first approximation is necessary in order to make a tentative selection of pipe sizes. If the computed pipe sizes differ from those used in deter mining the equivalent length of pipe fittings,.a recalculation will.be necessary, using the computed pipe sizes for the fittings. For the purposes of this example assume that the total equivalent length of the pipe fittings is 50 ft. Then the permissible pressure loss per 100 ft of equivalent pipe is 12 X 100/(100 + 50) = 8 psi. , Assuming that the corrosive and caking properties of the water are such that Fig. 4 for fairly rough pipe is applicable, a 2 in. building main will be adequate. The sizing of the brandies of the building main, the risers, and fixture branches follow the principles outlined. For example, assume that one of the branches of the building main carries the cold water supply for 3 water closets, 2 bath tubs, and 3 lavatories. Using the permissible pressure loss of 8 psi per 100 ft, the size of branch determined from Table 2 and Figs. 1 and 4 is found to be 1J^ in. Items entering the computation of pipe size are given in Table 6. The principles involved in sizing either up-feed , or down-feed systems are the same. The principal difference in procedure is that in the downfeed system, the difference in elevation between the house tank and the fixtures provides the pressure required to overcome pipe friction. The water demand for hose bibbs or other large demand fixtures taken off the building main is frequently the cause of inadequate water supply to the upper floor of a building. This condition may be prevented by sizing the distribution system so that the pressure drops from the street main to all fixtures are the same. It is good practice to maintain the building main of ample size (not less than I in. where possible) until all branches to hose bibbs have been connected. Where the street main pressure is excessive and a pressure reducing valve is used to-prevent water hammer or exces sive pressure at the fixtures, it is frequently desirable to connect hose bibbs ahead of the reducing valve. Table 6. Computation of Branch Size in Example 2 Fixtures No. and Kind Fixture Units (From Table 2 and Note c) 1 - Demand (From Fig. 2) Gpm 3 flush valves......... ............... 3 lavatories................................ 3x6 =18 I (2 x 2) = 3 I(3xl)= 2.25 23:25 38 Pipb'Size (From Fio. . 4) In. nv `