In order for the system to operate satisfactorily, the proper compressed air-to-water ratio must be maintained. Since air is soluble in water, the air charge in a plain tank must be constantly replenished by some type of

air volume control as in “A”, Fig. 2, or the compressed air must be separated from the water as shown in “B”, “C”, “D”. The Wafer, “B”, floats up and down on the water and, thus reduces air-to-water contact area, while the Diaphragm, “C”, and Bladder, “D”, hermetically seal the air from the water.

Diaphragm and Bladder type tanks are pre-charged with air at the factory. An air charging valve is provided in these types of tanks to allow the installer to change the pre-charge pressure. Pre-charging a tank increases the amount of water that can be withdrawn between operating cycles of the

pump. To select the proper pressure tank, follow the instructions below.

 

  1. Determine the peak demand for a seven minute period, which is the average time of higher water usage by such devices as automatic washers and showers. The Peak Demand is found by reading down the column in Table 2 under the number of bathrooms. For example, the Peak Demand for a home with 1½ bathrooms is 70 gallons.
  2. Follow the same column down to the “Minimum sized pump requirement”, which is 10GPM, or 600 GPH for the 1½ bathroom example.
  3. Check to make sure the well and the pump selected have sufficient capacity to meet or exceed the Peak Demand rate. If they do not, go to Step 4. If they do have sufficient capacity, select the tank from Table 3. Continuing with our 10 GPM example and assuming a pressure switch setting of 30 – 50 lbs per in2, it is found that an 80 gallon Plain steel tank would be required, compared to only a 45 gallon size in the Wafer type or 40 gallon for the bladder or diaphragm types. For farms or other installations requiring water in addition to household use, the extra gallons needed during the seven minute Peak Demand period must be estimated using Table 2. The additional gallons are then added to the amount found in Table 2, above. For instance, if the 1½ bathroom house, in the example above, had as estimated increase usage of 35 gallons during the peak demand period, the total water needed during the period would be 35+70 or 105 gallons. Divide 105 by 7 to get the use rate of 15 gallons per minute. Enter Table 3, for 30 – 50 lbs per in2 pressure, to find the tank size required, which is 150 gallon Plain steel, 80 gallon Wafer, or 75 gallon Bladder or Diaphragm types. If a standard tank is not available in the indicated size use the nest larger standard size.
  4. If the well and pump do not have the capacity to meet the Peak Demand, an extra large pressure tank, or a 2-pump system may be necessary. In a 2-pump system, the well pump pumps into a storage tank at a rate which does not exceed the well capacity. This pump is controlled by a switch actuated by water level in the storage tank. A second pump, of the centrifugal “booster” type, pumps from the storage tank to the pressure tank. It is actuated by a pressure switch. Consult your representative on specific installations requiring supplemental water storage.

Table 3:  Tank Selection Chart - Gallons

(based on present industry practices)

Pump

PGH

 

240

240

300

360

420

480

540

600

660

720

780

840

900

960

1020

1080

1140

1200

1400

1320

1380

1440

1500

1560

1620

1680

1740

1800

Capacity

GPM

 

4

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

Minimum

Drawdown

 (Gals)

 

4

4

5

6

7

8

9

10

12

13

15

17

19

20

23

25

27

30

33

36

38

41

44

47

50

53

57

60

Switch setting (Pounds per square inch)

20-40

40-60

30-50

A

 

20

20

30

35

10

40

50

55

60

70

80

90

100

110

120

135

150

160

175

190

205

220

235

250

270

285

305

320

 

B

 

15

15

20

20

25

30

30

35

40

45

50

60

65

70

80

85

95

105

115

120

130

140

150

160

175

185

195

205

C

 

15

15

15

20

20

25

30

30

35

40

45

55

60

65

70

80

85

95

105

110

120

130

140

145

155

165

175

190

 

A

 

30

30

40

45

55

65

70

80

95

105

120

135

150

160

185

200

215

240

265

290

305

330

350

375

400

425

460

480

 

B

 

20

20

25

25

30

35

40

45

50

60

65

75

80

90

100

110

120

130

140

155

165

175

190

205

230

230

245

260

 

C

 

15

15

20

25

25

30

35

40

45

50

60

65

75

75

90

95

105

115

125

140

145

150

170

180

190

205

220

230

 

A

 

40

40

50

55

75

85

95

105

125

135

155

175

195

205

240

260

280

310

340

370

390

425

455

485

515

550

590

620

 

B

 

20

20

25

30

40

45

50

55

65

70

80

90

105

115

125

140

150

165

180

190

205

225

225

260

275

290

310

330

 

C

 

20

20

25

30

30

35

40

45

55

60

70

75

85

95

105

115

125

140

150

160

175

185

185

215

230

240

260

275

 

Pressure Tank Selection - by Nelsen Corporation

Outlets

Flow rate

GPM

Total usage

Gallons

Bathrooms in home

1

1.5

2-2.5

3-4

 

Note: Values given are average and do not include higher or lower extremes. *Peak demand can occur several times during morning and evening hours. Additional requirements: Farm, irrigation and sprinkling are shown in part 3 of this section. These values must be added to the peak demand figures if usage will occur during normal demand periods.

 

Table 2: Seven minute peak demand period usage

 

Shower or bath tub

Lavatory

Toilet

Kitchen sink

Automatic washer

Dishwasher

Normal seven minute peak demand (gallons)

Minimum sized pump to meet peak demand

without supplemental supply

 

5

4

4

5

5

2

 

35

2

5

3

35

14

 

35

2

5

3

-

-

45

7 GPM

(420 GPH)

 

35

4

10

3

18

-

70

10 GPM

(600 GPH)

 

53

6

15

3

18

3

98

14 GPM

(840 GPH)

 

70

8

20

3

18

3

122

17 GPM

(1020 GPH)

Contact:

George Hogg

WTC

 

Email:

Copyright © 2015 Water by George

Cell:

 

Postal Address:

PO Box 12699

Lloydminster, AB T9V 0Y4