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To determine the maximum probable demand in gallons per minute corresponding to any given load in water supply fixture units, reference should be made to Table B.5.4, in which the values have been arranged for convenient conversion of maximum probable demand from terms of water supply fixture units of load to gallons per minute of flow. Refer to the increased number of WSFU to GPM listings in Appendix M to avoid the need to interpolate between the values in Table B.5.4.
Note in the table that the maximum probable demand corresponding to a given number of water supply fixture units is generally much higher for a system in which water closets are flushed by means of direct-supply flushometer valves than for a system in which the water closets are flushed by other types of flushing devices.
The difference in maximum probable demand between the two systems diminishes as the total number of fixture units of load rises. At 1,000 water supply fixture units, the maximum probable demand in both types of systems is the same, 210 gpm.
Where a part of the system does not supply flushometer water closets, such as in the case with hot water supply piping and some cold water supply branches, the maximum probable demand corresponding to a given number of water supply fixture units may be determined from the values given for a system in which water closets are flushed by flush tanks.
Table B.5.4
TABLE FOR CONVERTING DEMAND IN WSFU TO GPM1, 4
WSFU GPM Flush Tanks2 GPM Flush Valves3 WSFU GPM Flush Tanks2 GPM Flush Valves3
3 3 120 49 74
4 4 140 53 78
5 4.5 22 160 57 83
6 5 23 180 61 87
7 6 24 200 65 91
8 7 25 225 70 95
9 7.5 26 250 75 100
10 8 27 300 85 110
11 8.5 28 400 105 125
12 9 29 500 125 140
13 10 29.5 750 170 175
14 10.5 30 1000 210 210
15 11 31 1250 240 240
16 12 32 1500 270 270
17 12.5 33 1750 300 300
18 13 33.5 2000 325 325
19 13.5 34 2500 380 380
20 14 35 3000 435 435
25 17 38 4000 525 525
30 20 41 5000 600 600
40 25 47 6000 650 650
50 29 51 7000 700 700
60 33 55 8000 730 730
80 39 62 9000 760 760
100 44 68 10,000 790 790
NOTES:
  1. This table converts water supply demands in water supply fixture units (WSFU) to required water flow in gallons per minute (GPM) for the purpose of pipe sizing.
  2. This column applies to the following portions of piping systems:
    1. Hot water piping;
    2. Cold water piping that serves no water closets; and
    3. Cold water piping that serves water closets other than the flush valve type.
  3. This column applies to portions of piping systems where the water closets are the flush valve type.
  4. Refer to Appendix M for WSFU to GPM listings between those in Table B.5.4 to avoid the need to interpolate between the values in Table B.5.4.