Document 2qqq7825xy3N3VzYXB2qe9E76

American Society of Heating and Ventilating Engineers Guide, 1932 Care should be taken sufficiently to throttle the branches especially at points of high pressure so that the discharge will approximate the amounts given in Table 1. Unless the flow of water is throttled properly, broken fittings may result from excessive water h'ammer in addition to draining the pressure in the riser. The throttling should preferably be done by pipe sizing Table 1. Branch Pipe Sizes and Quantities for Various Fixtures Type of Fixture Pipe Size (In.) Lavatory____ ................ .............. . ..................... Bath...........................-.............;............... -........-- Shower, .Rain, Head................... ....................... Shower, Needle................................................... Tank, Urinal........................................................ Tank, W. .G.....;.u^.l,...S......... .-.U.^.......... . Urinal Flush Valve..................... .............. -...... Urinal Flush Valve...................... ..................... W. C. Flush Valve......... ........................... W; C. Flush Valve...................:........... Slop Sink, etc...................................................... H % l . -H % l l lH l Desired Discharge (gpm) 4 15 8 30 6 .. . 8 30 30 30 30 15 Probable Discharge (gpm) .5 14 5 28 5 :! is i 14; . 28 28 .49 :.. 14 . Table 2. Equivalent Pipe Sizes3 (Number of A-in. pipes accommodated by a single pipe at the same friction ' loss per unit of length based on Ds n using nominal sizes) ! _ ' Pipe Diameter ;; \ .' : .1 . Capacitt ob Factor Value Vs 3A .1 VA T .' I'A .2. . - " : 2'A 3 ' m 4 , - ' - ... 5- 6 8 1 2.7 .5.5 9.7 15.3 . . . . . -32 55 86.5 i27 178 310 . 490 1000 . .. ! . IO-i . ..... .. '; ; <The nominal size of pipe was used in the preparation of this table on account of the fact that the flow in several existing installations approached the values in the third column of Table 1 and which values follow closely along the estimated values of D*'* when the nominal sizes are taken. ....... rather than by means of control valves, since the latter concentrate all the resistance at one point which, with the necessary high velocity, causes a hissing, noisy system. To avoid the water hammer,' air chambers should be installed just before the fixtures, or a pressure-reducing, or flow regulating valve should be installed on the branch. Failure to consider the friction consumed by the meter has been the cause of unsatisfactory operation of the system in many cases;: The 206 Chapter- 13--Domestic Water Requirements and Pipe Sizes friction loss through the meter is sometimes .as much as that throughout the remainder of the system.. Its value can always be obtained from the makers of the particular meter used. - - SIZING OF MAINS AND RISERS The uncertainty of the flow in the.risers leaves some uncertainty as to the pressure that will prevail at any branch-take-off and precludes the sizing of the branch pipe with any degree of precision. This has led to the adoption of fixed sizes for. the various fixtures. These sizes, together .wi th the rate of flow desirable for the fixture and the probable amount of discharge that will result with the average length of branch, are given in Table 1. The discharge quantities which were taken from the equivalent values for the various diameters given in Table 2, follow closely the flow Fig. IVChart Showing Relation Between Floor Number andPer Cent of Simultaneous Use of Installed Fixtures for Proportioning Mains, Risers, and Headers. (The Floor Number is Taken as the Floor Nearest the Ground for Down-Feed Systems, and the Highest Floor for Up-Feed Systems) through a pipe with an equivalent length of 25 ft for a friction loss of 30 lb per square inch. It is. well to keep the following points in mind while designing the water supply piping: 1. .Liberal sizing of mains and risers is advisable. 2. Liberal sizing of the branches may cause trouble. 3. When liberal sized branches are used the risers, mains and tanks must be increased accordingly. 4. With proper care the risers and mains need not be made so large as to make the cost excessive. _ 5. To base the design on an assumed probability of simultaneous use may be dangerous. Probability of Simultaneous Use .._. The risers and mains must be sized to accommodate the discharge.from all the branches with due consideration to the probability of simultaneous 207