2025 Nelsen Corporation Catalog - Catalog - Page 446
17 Pressure Tank Selection
Technical & Engineering
TABLE 2: SEVEN MINUTE PEAK DEMAND PERIOD USAGE
OUTLETS
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
FLOW RATE
GPM
5
4
4
5
5
2
TOTAL USAGE
GALLONS
35
2
5
3
35
14
1
35
2
5
3
45
7 GPM
(420 GPH)
BATHROOMS IN HOME
11/2
2-21/2
35
53
4
6
10
15
3
3
18
18
3
70
98
10 GPM
14 GPM
600 GPH)
(840 GPH)
3-4
70
8
20
3
18
3
122
17 GPM
(1020 GPH)
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.
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 ai
r 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 precharge 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of water that can be withdrawn between operating cycles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
17 - 26
TABLE 3: TANK SELECTION CHART – GALLONS
(based on present industry practices)
Pump
Capacity
PGH GPM
240
4
Minimum
Drawdown
(Gals)
Switch Setting (Pounds per Square Inch)
20-40
30-50
40-60
A
B
C
A
B
C
A
B
C
4
20
15
15
30
20
15
40
20
20
20
240
4
4
20
15
15
30
20
15
40
20
300
5
5
30
20
15
40
25
20
50
25
25
360
6
6
35
20
20
45
25
25
55
30
30
420
7
7
10
25
20
55
30
25
75
40
30
480
8
8
40
30
25
65
35
30
85
45
35
540
9
9
50
30
30
70
40
35
95
50
40
600
10
10
55
35
30
80
45
40
105
55
45
660
11
12
60
40
35
95
50
45
125
65
55
720
12
13
70
45
40
105
60
50
135
70
60
780
13
15
80
50
45
120
65
60
155
80
70
840
14
17
90
60
55
135
75
65
175
90
75
900
15
19
100
65
60
150
80
75
195 105
85
960
16
20
110
70
65
160
90
75
205 115
95
1020
17
23
120
80
70
185 100
90
240 125 105
1080
18
25
135
85
80
200 110
95
260 140
1140
19
27
150
95
85
215 120 105 280 150 125
1200
20
30
160 105
95
240 130
115
115
310 165 140
1400
21
33
175
115
105 265 140 125 340 180 150
1320
22
36
190 120
110 290 155 140 370 190 160
1380
23
38
205 130 120 305 165 145 390 205 175
220 140 130 330 175 150 425 225 185
1440
24
41
1500
25
44
235 150 140 350 190 170 455 225 185
1560
26
47
250 160 145 375 205 180 485 260 215
1620
27
50
270 175
1680
28
53
285 185 165 425 230 205 550 290 240
155 400 230 190 515 275 230
1740
29
57
305 195
1800
30
60
320 205 190 480 260 230 620 330 275
175 460 245 220 590 310 260
A - plain steel tank, B - Supercharged, floating wafer tank,
C - Precharged bladder or diaphragm tank
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,
Continued Next Page
For more information visit – NelsenCorp.com • NelsenWaterSolutions.com • VESTAwater.com
All prices and products subject to change without notice. ©Nelsen Corporation
