Sizing Tanks - Pentair Pentek Series Electronic Manual

SECTION 14: Appendix
EXAMPLE
Assume we want 16 GPM at 60 PSI from a pump
drawdown level (pumping level) 100 feet below the
service inlet.
We have a 35 foot horizontal run of 1 1/4" plastic pipe
with two gate valves and four 90° elbows.
To find the Friction losses we must refer to friction loss
charts for pipe and fittings.
We find:
• 135 feet of pipe for the total pipe run (100 + 35).
• 10 equivalent feet of pipe for the gate valves (2 x5)
• 28 equivalent feet of pipe for the elbows (7x 4)
Add these for the total equivalent length of pipe = 173
• In the friction loss charts, find the loss of head for
173 feet of 1 1/4" pipe at 16 gpm. (3.96 per 100') = 3.96
x 1.73 = 6.8 (round to 7.0)
Add: 7 Friction loss
100 Pumping level
139 60 PSI service pressure required (60
x 2.31=138.6. Round to 139)
= 246 Total Dynamic Head.
From this sample curve we would choose the
1 1/2 HP pump.
Locate a pump with a best efficiency point near the
desired flow rate (16 GPM) that meets the total head
requirements (246 TDH).
Selecting a pump in this manner gives you the most
efficient pump for your application.
CAPACITY LITRES PER MINUTE
0 25 50
600
500
400
300
200
100
0 5 10
CAPACITY GALLONS PER MINUTE
Sample Pump Curve
104
75 100
15 20 25 30

14.5 Sizing Tanks

Tank should be sized to accomodate starting frequency in
Section 5.10.
Refer to the dealer catalog for tank selection. Otherwise,
the following procedure can be used.
Drawdown based on Boyle's Law
Procedure:
1. Identify drawdown multiplier relating to
specific application.
2. Insert multiplier (X) into the following formula:
Pump GPM x Min Run Time
Multiplier (X)
Example: An example of a 20 GPM pump with a
minimum run time of 1 minute, installed on a
50 - 70 PSIG system pressure range:
20 GPM x 1 minute
.24 (factor)
NOTICE: Drawdown will be affected by operating
temperature of the system, accuracy of the pressure
switch and gauge, the actual pre-charge pressure and the
rate of fill.
Table 12-2: Drawdown Volume Multiplier
(Approximate)
Pump Off
Pressure
10
PSI
20 0.26
30 0.41
40
50
60
175
70
80
150
90
100
125
Ta nk sizing for Variable Frequency Drives
Variable Frequency Drives (VFD) may require slightly
100
different methods for figuring tank size. Refer to
Section 8 for VFD information.
75
50
25
0
= Minimum Tank
Capacity Required
= 83.3 minimum U.S.
gallon tank capacity
Pump Start Pressure – PSI
20 30 40 50 60
0.22
0.37 0.18
0.46 0.31 0.15
0.40 0.27 0.13
0.47 0.35 0.24 0.12
0.42 0.32 0.21
0.48 0.38 0.29
0.44 0.35
70 80
0.11
0.19 0.10
0.26 0.17