UFC 3-280-04
17 DEC 2003
change; the transfer pump should be sized to deliver a minimum flow of 2.15 L/s (33
gpm) at 172.6 kPa (25 psi) maximum head loss. Based on manufacturer's literature and
texts, the flow across the filter bed should not exceed 3.4 L/m2 s (5 gpm/ft2) x 1.17 m2
(12.56 ft2) for the 122-cm (48-in.) diameter filter or 4.0 L/s (63 gpm) when the bed is
clean. We will use 2.70 L/m2 s (4 gpm/ft2) or 3.16 L/s (50 gpm) to provide a small factor
of safety and ensure that the backwash frequency is not excessive. The maximum flow
rate for the transfer pump should not exceed 3.2 L/s (50 gpm) at 104.0 kPa (15 psi) for
clean media. The specification for the transfer pump should indicate both operating
conditions, 2.15 L/s (33 gpm) at 172.6 kPa (25 psi) and not greater than 3.16 L/s (50
gpm) at 104.0 kPa (15 psi). Limiting the range of flow over the entire filter cycle is
preferable to avoid the need for pacing the flow of chemical addition, if possible.
B-10
BACKWASH PUMP. Discussions with the filter manufacturer about this de-
sign example yield the recommendation that the backwash pump be specified to de-
velop a pressure of 4.22 kg/cm2 (60 psi). Backwash flow rate:
10.17 L/m2 s 1.167 m2 = 11.87 L/s
(15 gpm/ft2 12.56 ft2 = 188 gpm).
B-11
SYSTEM SUMMARY
1 - 18,000-L (5000-gal.) equalization tank.
1 - Transfer pump: 2.2 L/s (33 gpm) at 172.6 kPa (25 psi) and < 3.16 L/s (50
gpm) at 104.0 kPa (15 psi).
1 - Chemical feed system: Permanganate addition for manganese oxidation.
1 - Pressure filter: 1.22-m (48-in.) diameter with dual media (anthracite and
silica sand 0.76 m [30 in.] deep).
1 - 7250-L (2000-gal.) backwash holding tank.
1 - Backwash pump: 11.87 L/s (188 gpm) at 413.8 kPa (60 psi).
1 - Air stripper.
1 - Dual carbon adsorption system.
Make provisions for future addition of backwash thickening tank if required.
Figure B-1. Example Pressure Filter
B-4
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