
17
PIPE FRICTION CALCULATIONS
CAPACITY AND HEAD IN FEET: Gallons per minute (gpm) and Foot Heads in the performance charts in this manual were compiled from
actual tests. The Maximum gpm shown is the pump capacity at rated horsepower. The maximum Head in Feet is at full rated speed (60 cycle
current). For Maximum gpm, all piping should be straight, short and large as possible. Heads and gpm are based on tests with specific gravity
of 1 and a temperature of 70°F.
HOW TO FIGURE HEAD:
1. Determine static lift (height liquid is to be raised above reservoir)
2. Determine friction loss (losses due to piping depend on size, length and condition of piping system in relation to gpm needed, see table
below. Friction losses also include loss due to valves and fittings)
3. Determine velocity head (refer to table below)
4. Total all three of the above and compare to performance chart. Select pump which delivers total head at desired gpm.
PIPE FRICTION
Loss of Head in Feet per 100 ft of 15-year-old ordinary iron pipe due to friction.
Gallons
per
Minute
1
/
2
”
Pipe
3
/
4
”
Pipe
1”
Pipe
1
1
/
4
”
Pipe
1
1
/
2
”
Pipe
2”
Pipe
2
1
/
2
”
Pipe
3”
Pipe
Vel. Fric. Vel. Fric. Vel. Fric. Vel. Fric. Vel. Fric. Vel. Fric. Vel. Fric. Vel. Fric.
1 1.05 2.1 ------ ------ ------------------------------------------------------------------------
2 2.10 7.4 1.20 1.9 ------------------------------------------------------------------------
3 3.16 15.8 1.80 4.1 1.12 1.26 ------------------------------------------------------------
4 4.21 27.0 2.41 7.0 1.49 2.14 0.86 0.57 0.63 0.26 ------------------------------------
5 5.26 41.0 3.01 10.5 1.86 3.25 1.07 0.84 0.79 0.39 ------------------------------------
10 10.52 147.0 6.02 38.0 3.72 11.7 2.14 3.05 1.57 1.43 1.02 0.5 0.65 0.17 0.45 0.07
15 ------ ------9.02 80.0 5.60 25.0 3.2 6.5 2.36 3.0 1.53 1.0 0.98 0.36 0.68 0.15
20 ------ ------12.03 136.0 7.44 42.0 4.29 11.1 ----- ------ ------ 1.83 1.31 0.61 0.91 0.25
25 ------ ------------------9.30 64.9 5.36 16.6 3.94 7.8 2.55 2.73 1.63 0.92 1.13 0.38
30 ------ ------------------11.15 89.0 6.43 23.5 4.72 11.0 3.06 3.84 1.96 1.29 1.38 0.54
35 ------ ------------------13.02 119.0 7.51 31.2 5.51 14.7 3.57 5.1 2.20 1.72 1.59 0.71
40 ------ ------------------14.88 152.0 8.58 40.0 6.3 18.8 4.08 6.6 2.61 2.20 1.82 0.81
45 ------ ------------------------------9.65 50.0 7.08 23.2 4.60 8.2 2.94 2.80 2.05 1.15
50 ------ ------------------------------10.72 60.0 7.87 28.4 5.11 9.9 3.29 3.32 2.27 1.38
70 ------ ------------------------------15.01 113.0 11.02 53.0 7.15 18.4 4.58 6.2 3.18 2.57
90 ------ ------------------------------------------ 14.17 84.0 9.19 29.4 5.88 9.8 4.09 4.08
100 ------
------------------------------------------15.74 102.0 10.21 35.8 6.54 12.0 4.54 4.96
120 ------
------------------------------------------18.89 143.0 12.25 50.0 7.84 16.8 5.45 7.0
140 ------
------------------------------------------22.04 190.0 14.30 67.0 9.15 22.3 6.35 9.2
160 ------
------------------------------------------------------16.63 86.0 10.48 29.0 7.26 11.8
180 ------
------------------------------------------------------18.38 107.0 11.76 35.7 8.17 14.8
200 ------
------------------------------------------------------20.42 129.0 13.07 43.1 9.08 17.8
220 ------
------------------------------------------------------22.47 154.0 14.38 52.0 9.99 21.3
240 ------
------------------------------------------------------24.51 182.0 15.69 61.0 10.89 25.1
260 ------
------------------------------------------------------26.55 211.0 16.99 70.0 11.80 29.1
280 ------
------------------------------------------------------------ ------ 18.30 81.0 12.71 33.4
300 ------
------------------------------------------------------ ------ ------ 19.61 92.0 13.62 38.0
PIPE FRICTION (continued)
Loss of Head in Feet per 100 ft of 15-year-old ordinary iron pipe due to friction.
Gallons
per
Minute
4” Pipe 5” Pipe
6”
Pipe
Vel. Fric. Vel. Fric. Vel. Fric.
40 1.02 0.22 ------ ------ ------ ------
5 1.17 0.28 ------ ------ ------ ------
50 1.28 0.34 ------ ------ ------ ------
70 1.79 0.63 1.14 0.21 ------ ------
75 1.92 0.73 1.22 0.24 ------ ------
00 2.55 1.23 1.63 0.39 1.14 0.14
120 3.06 1.71 1.96 0.57 1.42 0.25
125 3.19 1.86 2.04 0.64 1.48 0.28
150 3.84 2.55 2.45 0.88 1.71 0.32
175 4.45 3.36 2.86 1.18 2.0 0.48
200 5.11 4.37 3.27 1.48 2.28 0.62
225 6.32 6.61 3.67 1.86 2.57 0.74
250 6.40 6.72 4.08 2.24 2.80 0.92
275 7.03 7.99 4.50 2.72 3.06 1.15
300 7.66 8.38 490 3.15 3.40 1.29
350 8.90 12.32 5.72 4.19 3.98 1.69
400 10.20 15.82 6.54 5.33 4.54 2.21
450 11.50 19.74 7.35 6.65 5.12 2.74
475 12.30 22.96 7.88 7.22 5.55 3.21
500 12.77 22.08 8.17 8.12 5.60 3.26
550 ------ ------ 9.09 9.66 6.16 3.93
600 ------ ------ 9.80 11.34 6.72 4.70
650 ------ ------ 10.62 13.16 7.28 5.60
700 ------ ------ 11.44 15.12 7.84 6.38
750 ------ ------ 12.26 17.22 8.50 7.0
800 ------ ------ ------ ------ 9.08 7.90
850 ------ ------ ------ ------ 9.58 8.75
900 ------ ------ ------ ------ 10.30 10.11
950 ------ ------ ------ ------ 10.72 10.71
1000 ------ ------ ------ ------ 11.32 12.04
1100 ------ ------ ------ ------ 12.50 14.31
1200 ------ ------ ------ ------ 13.52 16.69
Friction of Water in 90° Elbows
Size of Elbow,
Inches
1
/
3
/
4
1 11
/
4
1
1
/
2 21
/
3 4 5 6
Friction Equivalent,
Feet Straight Pipe
5 6 6 8 8 8 11 15 16 18 18
To Compute Break Horsepower
BHP= GPM x H x S.G.
3960 x pump eff*
S.G. = Specific Gravity
BHP = Break Horsepower
GPM = Gallons per Minute
H = Head in Feet
Eff = Efficiency
Horsepower and Pressure (PSI) vary in direct
proportion to the Specific Gravity.
Effect of Speed Changes
1. Capacity (GPM) is directly proportional to the
change in speed.
2. Head is proportional to the square of the change
in speed.
3. Horsepower is proportional to the cube of the
change in speed.