3-8 Calculating Friction Loss In Hose LaysFriction Loss Formulas
and Calculations
FL = (C x Q2)(L)
Friction Loss Formula
FL = (C x Q2)(L)
C = Coefficient for hose diameter
Q = Quantity
L = Length
FL Coefficients
C factors refer to the third principle of friction
loss
The base of the friction loss equation
Assigned based on the diameter of the hose
FL decreases as diameter increases
Reflects a worst-case scenario
Results are probably slightly higher
Standard (Coefficients)
1"=150
1½"=24
1¾"=10
2½"=2
3"=0.8
4"=0.2
4½"=0.1
5"=0.08
Calculating "Q"
Q = 200 (gpm)/100
Q = 2
If gpm is 400, what is Q?
Q = 400 (gpm)/100
Q = 4
Second step of formula
Must be calculated, then applied
If gpm is 200, what is Q?
FL = (2 x 22)(1)
FL = (2 x 4)(1)
FL = (8)(1)
FL = 8 psi
200
gp
m 100' of 2½"
Calculating FL
FL = (2 x 12)(3)
FL = (2 x 1)(3)
FL = (1)(3)
FL = 6 psi
100
gp
m 300' of 2½"
Calculating Single Hose FL
Multiple Hoselines -Equal Size/Length
Calculate FL for
one hoseline only if other
hoselines will have the same
pressure and gpm
1" at 50
psi
400' of 2½"Calculate Q
gpm = (29.7)(d2 x NP)
gpm = (29.7)(12 x 50)
gpm = (29.7)(1 x 7.0711)
gpm = (29.7)(7.0711)
gpm = 210 psi = 200 psi
Q = 200/100 = 2
1"
nozzles
400'of 2½"Calculate
FL
FL = (C x Q2)(L)
FL = (2 x 22)(4)
FL = (2 x 4)(4)
FL = (8)(4)
FL = 32 psi
Wyed Hoselines -Equal Lengths
One hoseline supplies two others
Two 1½" or 1¾" attack lines wyed from a 2½"
supply line is common
Calculate FL for supply line and one wyed
hoseline, then add together
Only one needs to be computed since they
carry equal amounts of water
Wye Line
Q = 150
100
Q = 1.5
2½" Line
Q = 300
100
Q = 3
Calculate Q
200' of 2½"
150
gpm
150' of 1¾"
Calculate FL
200' of 2½"
150
gpm
150' of 1¾"
2½" Line
FL = (C x Q2)(L)
FL = (2 x 32)(2)
FL = (2 x 9)(2)
FL = (18)(2)
FL = 36 psi
34 psi
36 psi
70 psi
Wye Line
FL = (C x Q2)(L)
FL = (10 x 1.52)(1.5)
FL = (10 x 2.25)(1.5)
FL = (22.5)(1.5)
FL = 34 psi
Siamese Hoselines -Equal Length
Two or more parallel hoselines
Divide gpm by total number of hoselines
Then calculate FL for one line
Take ½ of the gpm flow and figure the FL for
one line
Coefficients are used in calculating FL
2½" Line
Q = 300
100
Q = 3
Siamese
Q = 150
100
Q = 1.5
1,000' of 3"
300
gpm
1,000' of 3"
300' of 2½"
Calculate Q
1,000' of 3"
300
gpm
1,000' of 3"
300' of 2½"
Calculate FL
2½" Line
FL = (C x Q2)(L)
FL = (2 x 32)(3)
FL = (2 x 9)(3)
FL = (18)(3)
FL = 54 psi
Siamese
FL = (C x Q2)(L)
FL = (.8 x 1.52)(10)
FL = (.8 x 2.25)(10)
FL = (1.8)(10)
FL = 18 psi
1,000' of 3"
300
gpm
1,000' of 3"
300' of 2½"
Calculate FL
Add FL together
54 psi
18 psi
72 psi
Multiple Hoselines -Unequal Length
Calculate FL for each line
Pump for highest pressure needed
Gate down discharge of line(s) needing less
pressure
Calculating Q
Q = 250
100
Q = 2.5
250
gpm
300' of 2½"
500' of 2½"
250
gpm
Line 1:
300' of 2½"
Line 2:
500' of 2½"
Calculate FL
Line 2
FL = (C x Q2)(L)
FL = (2 x 2.52)(5)
FL = (2 x 6.25)(5)
FL = (12.5)(5)
FL = 63 psi
Line 1
FL = (C x Q2)(L)
FL = (2 x 2.52)(3)
FL = (2 x 6.25)(3)
FL = (12.5)(3)
FL = 38 psi
63 psi
Wyed Hoselines -Unequal Length
Addition of hose lengths to an existing wyed
hoseline assembly may result in unequal
length attack lines
Calculate FL for supply line and both wyed
hoselines
Pump to the highest wyed line and gate-down
the other wyed line
Calculate Q
200' of 2½"
100
gpm
200' of 1½"
150' of 1½"
Wye Line
Q = 100
100
Q = 1
2½" Line
Q = 200
100
Q = 2
Calculate FL
150' Wye Line
FL = (C x Q2)(L)
FL = (24 x 12)(1.5)
FL = (24 x 1)(1.5)
FL = (24)(1.5)
FL = 36 psi
2½" Line
FL = (C x Q2)(L)
FL = (2 x 22)(2)
FL = (2 x 4)(2)
FL = (8)(2)
FL = 16 psi
200' of 2½"
100
gpm
200' of 1½"
150' of 1½"
200' Wye Line
FL = (C x Q2)(L)
FL = (24 x 12)(2)
FL = (24 x 1)(2)
FL = (24)(2)
FL = 48 psi
Calculate FL
48 psi
16 psi
63 psi
200' of 2½"
100
gpm
200' of 1½"
150' of 1½"
October 2008 Slide 3-8-26
Siamese Hoselines -Unequal Length
Add the lengths of each line together, then
divide by total number of lines
2½" Line
Q = 250
100
Q = 2.5
Siamese
Q = 125
100
Q = 1.25
900 of 3"
250
gpm
1,000' of 3"
100' of 2½"
Calculate Q
900 of 3"
250
gpm
1,000' of 3"
100' of 2½"
Calculate FL
Determine L
900
1,000
1,950
1,950 2 = 950
950 100 = 9.5
Siamese
FL = (C x Q2)(L)
FL = (.8 x 1.252)(9.5)
FL = (.8 x 1.56)(9.5)
FL = (1.25)(9.5)
FL = 12 psi
900 of 3"
250
gpm
1,000' of 3"
100' of 2½"
Calculate FL
2½" Line
FL = (C x Q2)(L)
FL = (2 x 2.52)(1)
FL = (2 x 6.25)(1)
FL = (12.5)(1)
FL = 13 psi
13 psi
12 psi
25 psi