The bacterial efficiency of gravity filters depends upon the use of coagulants. If clear water for industrial purposes is wanted, it may be had by filtering through sand without coagulant, but for domestic water supply, where bacterial purity is required, coagulants must be used. The tabulated report of chemical and bacterial tests of gravity water filters, at Lorain, Ohio, for week ending March 12, 1904 (see Table XL), will serve to show the efficiency of rapid sand filters.

The standard sizes, weights, capacities, etc., of the

Jewell Subsidence Gravity Filter can be found in Table XLI.

A plan of a filter house for a small city plant, showing the layout of filters, piping and apparatus, is illustrated in Fig. 112.

Pressure filters are enclosed in water-tight chambers, so that water can be driven through the filter bed by hydraulic pressure. A Jewell pressure filter of the settling basin type is shown in Fig. 113. This filter is constructed and operated similar to the Jewell gravity type, from which it differs only by being enclosed in a water-tight case. Pressure filters are not as efficient as gravity filters, but owing to the ease with which they can be attached to a water supply system they are extensively used for house filters. Usually pressure filters are connected to the service pipe in the cellar, and all water used in the building passes through them. When so installed they should be provided with a by-pass to permit unfiltered water being supplied to fixtures in the building in case the filter is cut out. The bacterial efficiency of pressure filters like that of gravity filters depends upon the use of coagulants. When water is to be used for manufacturing purposes, however, a clear filtrate can be obtained without coagulants. An automatic apparatus is used to feed coagulant to pressure filters. The standard sizes, capacities, weights and dimensions of Jewell pressure filters, with settling basins, can be found in Table XLII.

Efficiency Of Gravity Filters 134

Fig. 113

Table XLI - Dimensions And Capacity Of Jewell Gravity Filters

Size

Connections, in Inches

Capacity

Area

Bed

Shipping

Weights

(Approximate)

Total Wgt.

Diameter in Feet

Supply and Discharge Pipe

Washout Pipes

Minimum and Maximum, U. S. Gallons

Effective Filtering Surface, Sq. Feet

Filtering Material Cubic Feet

Machine Work Pounds

Tank Material

Cypress or Cedar

Cwt.

Filtering Material Tons

Filter in Operation Tons, about

Filter Bed

Tank

(Inside)

Main Tank (Outside)

Minute

Hour

Day 24 Hours

Settling Basin

6

7

3

6

47-94

2,800-5,600

62,500-125,000

1,500

28

118

1,000

50

5

15

8

9 1/4

4

6

82 164

5 000 10 000

120 000 240 000

2 600

50

200

1 800

70

9

28

10

11 1/2

4

8

180-260

7,800-15,600

185,000-370,000

4,000

78

312

2,500

105

14

45

12

13 1/2

5

8

188-376

11,300-22,600

250,000-500,000

5,750

118

452

3,750

125

20

70

14

15 1/2

6

8

255-510

15,300-30,600

865,000-730,000

8,000

153

612

5,000

145

27

100

17

18 2/3

6

8

376-752

22 600-45,200

500,000-1,000 000

11,500

226

904

9,500

180

40

145

21

22 3/4

8

2- 8

565-1,130

33,900-67,800

750,000-1,500,000

17,000

339

1,356

12,000

220

60

200

24

26

10

2-10

753-1,506

45,200-90,400

1,000,000-2,000,000

23,000

452

1,808

17,000

300

80

295

Standard height of filters, 14 feet. Depths of filter beds, 4 feet.