2023 Online Catalog - Flipbook - Page 488
17 Pressure Tank Selection
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
BATHROOMS IN HOME
1
1 /2
2-2 /2
3-4
35
35
53
70
2
4
6
8
5
10
15
20
3
3
3
3
18
18
18
3
3
45
70
98
122
7 GPM
10 GPM 14 GPM 17 GPM
(420 GPH) 600 GPH) (840 GPH) (1020 GPH)
1
1
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 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that can be withdrawn between operating cycles of the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.
TABLE 3: TANK SELECTION CHART – GALLONS
(based on present industry practices)
Technical & Engineering
4
Pump Capacity
Minimum
PGH GPM Drawdown (Gals)
Switch Setting (Pounds per Square Inch)
20-40
30-50
40-60
B
C
A B
C
A
B
A
C
240
4
4
20
15
15
30 20
15
40
20
20
240
4
4
20
15
15
30 20
15
40
20
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
95 260 140 115
1140
19
27
150
95
85 215 120
105 280 150 125
1200
20
30
160 105 95 240 130
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
1440
24
41
220 140 130 330 175
150 425 225 185
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
270 175 155 400 230
190 515 275 230
1680
28
53
285 185 165 425 230
205 550 290 240
1740
29
57
305 195 175 460 245
220 590 310 260
1800
30
60
320 205 190 480 260
230 620 330 275
A - plain steel tank, B - Supercharged, floating wafer tank, C - Precharged bladder or diaphragm tank
For more information visit – NelsenCorp.com
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.
• Commercial.NelsenCorp.com •
All prices and products subject to change without notice. ©Nelsen Corporation
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