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American Society of Heating and Ventilating Engineers Guide, 1935
the top floor, that the length of run from the tank to the farthest fixture is 200 ft, equiva lent length of fittings 100 ft, and the pressure required at the fixture is 7 lb.
The 30-ft head is equal to a static pressure of 0.43 X 30 or 12.9 lb per square inch and to maintain a pressure of 7 lb at the highest fixtures the drop allowable in pressure is 12.9 -- 7.0 lb or 5.9 lb. As the total equivalent run is 300 ft, this is a drop per 100 ft of 1.97 lb, or practically 2 lb. Therefore, all risers and mains from the top floor back to the
Table 4. Typical Calculation of Pipe Sizes on Down-Feed Riser with Flush Valve Water-Closets and Urinals
Floor
of
Bldg.
Fixtures --Gpm-- on PER
Floor Fixture
Riser No. 1. (See Fig. 4)
Maximum Probable' Probable
Fixtures
Use
Fixtures
Gpm (per cent) Gpm
____ --
Probable Allowable
Riser
Drop
Gpm J/B per 100 Ft
In.
1st I S. S. 2nd 1 S. S.
4 4
3rd 1 S. S. 4
3
4th 10 Lav.
3
13
6tb
4 W. C.
50
2 U. 40
6 3 Lav.
3
16
4 100 4 ` 100
4 12 80 30 42 45 200 80 280 40 9 51 45
44 4
8
10 10
19 19
112 22 134
30 X 30 X 30 . X 30 1, .
30 2
6th
4 W. C.
50
2 U. 40
12 3 Lav.
3
19
7th
4 W. C.
50
2 U. 40
IS
3 Lav. 22
3
200 80 560 25
9 60 42
200 80 840 18
9 69 40
140 25 165
--
151 28 179
30 2
<-
30 2X
8th
4 W. C.
50
2 U.
40
200 80
24 1120 15
3 Lav.
3
9
168
25
78 40
31 199
--
24
tank must be sized on the basis of a drop of 2 lb per 100 ft. Tables 4, 5, 6 and 7 show the schedule for Risers No. 1, 2 and 3 with the maximum possible flow taken from Table 1, the percentage of use at the peak taken from Fig. 1, and the maximum probable flow at the peak worked out for each portion of the riser, the riser sizes being taken from Table 2 as far as possible and from Fig. 3 where the amounts exceed the values given in this table; a drop of 30 lb per 100 ft is used except on the riser from the top floor back to the tank where 2 lb per 100 ft is the allowable limit.
The reduction in pipe size which would occur if flush tank water-closets were used on the top floor and only 3 lb pressure used on the fixtures is given in Tables 8 and 9.
608
Chapter 35--Water Supply Piping
This illustrates why flush tank closets so frequently are substituted on the uppermost
floor when a house tank is the source of water pressure: If it is now assumed that Riser No. 1 is to be fed from the bottom and the minimum
street pressure is 75 lb with the top fixture of the riser 80 ft above the main, the problem
Table 5.' Typical Calculation of Pipe Sizes on Down-Feed Riser with Flush Valve Water-Closets.and Urinals...................
Riser No. S. (See Fig. 4)
Floor Fixtures
of on
. Bldg. - _ Floor -
Gpm
Maximum Probable Probable Probable Allowable
per Fixtures
Use
.Fixtures - Riser--
Drop
Fixture- Gpm (per cent) Gpm
Gpm Lb per 100 Ft
Pipe . SizeIn.
1st
1 W. C.
50
2nd
2 W. C.
50
1 U. 40
4 1 Lav.
3
3rd
4 W. C.
50
2 U. 40
10 3 Lav.
3
4
50 100 100 40 190 50
3 100
200 80 470 30 9 12 70
50 50 95
3 98
141 8 149
30 IX 30 IX
30 2
4th
4 W. C.
50
2 U. 40
16 3 Lav. .
3
7
200 80 750 20 9 21 70
150 14 164
30 2
5th
6 W. C.
50
300
22. 4 Lav.
1050 3 12
15
11 33 48
157 - 16 173
30 2
6th
6 W. C.
50
300
28 4 Lav.
- 1350 3 12
12
15 45 . 45
7th
6 W. C.
50
34-~4 Lav.
3
19
300 1650 .
12 57 -
10 42
8tb
6 W. C.
50
300
40 4 Lav.
1950 3 -12
23 69
9 40
162 20. 182
30 2
165 ................ 24 189
30
.....
2X
175 ... - ... --
27 202-
2" :>4
would be solved by determining the maximum rate of flow in each portion of the riser as shown in Table 10 and then finding the allowable drop which can be used per 100 ft. The 80 ft of riser height will use up
.-
0.43.1b X 80 = 34.4 lb
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