Document LoX6JxEDLMzKBbK83Q3Xb3mxQ

HEATINC VENTILATING AIR CONDITIONING GUIDE 1942 The minimum practicable size of piping for any water system is governed by the amount of pressure which can be spared in overcoming resistance to flow of a given volume of water per unit of time. After the approximate amount of water required has been computed, a minimum' delivery pressure at the highest fixture may be determined. This will be approximately 15 lb per square inch for flush valve closets or 5 lb per square inch for gravity tank closets. It should be remembered that for every foot in height there will be a hydrostatic loss of approximately 0.4331b. The pressure loss through a water meter may be significant as may be seen from Table 2. The pressure losses through filters or other water conditioning apparatus must also be considered. After evaluating the previously mentioned factors, the total allowable friction loss for the CHAPTER 46. WATER SUPPLY PIPINC AND WATER HEATING If the building is in a zone having untreated water known to carry precipitable solids, the pipe sizes should be increased at least one size and no water pipe should be smaller than % in. Table 2. Pressure Loss Through Water Disc Meters3 A.W.W. A. Standards Fig. 1. Chart Showing Relation Between Maximum Flow and Probable Usage system may be determined by subtracting from the street main pressure, the sum of the following four items: 1. Minimum allowable pressure at top fixture. 2. Meter loss. 3. 0.433 X height in feet from main to top fixture. 4. Loss for filters, softener, etc. PIPE MATERIAL The material used in the water piping affects its carrying capacity. For example, copper or brass pipe is not as likely to retain interior incrustation as is ferrous pipe, and galvanized pipe will not rust as quickly as uncoated pipe. Some waters tend to deposit salts, rust, and the like on the interior surfaces of pipes, greatly reducing their capacity. In some cities it has been found necessary to allow for as much as 50 per cent reduction in carrying capacity after 15 years of service. The data given in this chapter are based on use of galvanized steel piping and on water which is not notoriously inclined to leave deposit. 816 ^Pressure loss through compound and current meters is less than shown in table. For exact information consult manufacturers. 817