Document 805nGrpjZm9ERLKDxOVMm9do

1178 CHAPTER 49 1957 Guide Table 1. Proper Flow and Pressure Required During Flow for Different Fixtures Fixture Flow Pressure* Flow gpm 8 12 10 5 5 5 12 15 10-20 15 30 3.0 2.5 4.5 4.5 6.0 5.0 5.0 3.0 15-40b 15.0 5.0 * Flow pressure is the pressure in the pipe at the entrance to the particular fixture considered. b Wide range due to variation in design and type of flush-valve closets. In general, a daily per capita water consumption of 40 gal can be used as a safe design figure for housing projects. Table 1 gives the rate of flow desirable for many common types of fixtures, and the average pressure necessary to give this rate of flow. The pressure necessarily varies with fixture design; with some, a much greater pressure is necessary to give the same rate of flow than with others. In general, the lower the quality of the faucet the greater will be the pressure required. In estimating the load, the rate of flow is frequently computed in fixture units. One fixture unit is equivalent to 7.5 gal per min. Table 2 gives the demand weights in terms of fixture units for different plumbing fix tures under several conditions of service, and Fig. 1 gives the estimated demand in gallons per minute corresponding to any total number of fix ture units. Fig. 2 shows an enlargement of Fig. 1 for a range up to 250 fixture units. Table 2. Demand Weights of Fixtures in Fixture Units* Fixture os Group* Occupancy PiihltV Type of Supply Control Combination -------------- Private-- ------- Faucet......... -........... .............. Weight in Fixture Units* 10 s 10 6 3 2 4 4 3 4 6 3 1 2 2 g 6 2 2 3 3 * For supply outlets likely to impose continuous demands, estimate continuous supply separately and add to total demand for fixtures. b For fixtures not listed, weights may be assumed by comparing the fixture to a listed one using water in timilaj quantities and at similar rates. 0 The given weights are for total demand. For fixtures with both hot and oold water supplies, the weights for maximum separate demands may be taken as the listed demand for the supply. Water Services 1179 No. I for system predominantly for flush valves. No. 2 for system predominantly for flush tanks. Fio. 1. Estimate Curves for Demand Load The estimated demand load for fixtures used intermittently on any supply pipe will be obtained by multiplying the number of each kind of fixture supplied through that pipe by its weight from Table 2, adding the products, and then referring to the appropriate curve of Figs. 1 or 2 to find the demand corresponding to the total fixture units. In using this method it should be noted that the demand for fixture or supply outlets other than those listed in the table of fixture units is not yet in cluded in the estimate. The demands for outlets (such as hose connec tions, air conditioning apparatus, etc.) which are likely to impose con tinuous demand during times of heavy use of the weighted fixtures, should be estimated separately and added to the demand for fixtures used in termittently, in order to estimate the total demand. So far, the information presented makes possible the determination of the design rate of flow in any particular section of piping. The next general step is to determine the size of piping. As water flows through a pipe, the pressure continually decreases along the pipe, due to loss of energy from friction. The problem is then one of ascertaining the minimum pressure in the street main, and the minimum Fio. 2. Section of Fio. 1 on Enlarged Scale i