Formula For Calculating FL

Question 1

The formula for calculating friction loss is: FL = CQ2L

1. FL=
2. C =
3. Q =
4. L =

Answer 1

1. friction loss in psi
2. friction loss coefficient
3. flow rate in hundreds of gpm (flow/100)
4. hose length in hundreds of feet (length/100)

Question 2

Example 7:

Friction loss in 200’ of 13⁄4” hose flowing 175gpm.

Answer 2

Friction loss in 200’ of 13⁄4” hose flowing 175gpm.

= 10 * Q^2 per 100 feet of hose( Q=gpm/100)
= 10 * Q^2 per 100’
= 10* 1.75^2 * 2
= 10 * 3.06 * 2
= 30.6 * 2
=61.2 psi

Question 3

Example 8:

Friction loss in 200 feet of 21⁄2” hose with 11/8” tip flowing 266 gpm.

Answer 3

Friction loss in 200 feet of 21⁄2” hose with 11/8” tip flowing 266 gpm.

FL = 2 x Q2 per 100 feet of hose (Q = gpm ÷ 100) 
= 2 x Q2 per 100' 
= 2 x 2.662 x 2 
= 2 x 7.08 x 2 
= 14.6 x 2 
= 28.32 psi

Question 4

Example 9:

Friction loss in 500’ of 3” hose supplying a mercury monitor flowing 500
gpm.

Answer 4

Friction loss in 500’ of 3” hose supplying a mercury monitor flowing 500 gpm.

FL = 0.8 x Q2 per 100 feet of hose (Q = gpm ÷ 100) 
= 0.8 x Q2 per 100' 
= 0.8 x 52 x 5 
= 0.8 x 25 x 5 
= 20 x 5 
= 100 psi

Question 5

Example 10:

Friction loss in 600’ of 4” hose supplying a pumper flowing 750 gpm.

Answer 5

Friction loss in 600’ of 4” hose supplying a pumper flowing 750 gpm.

FL = 0.2 x Q2 per 100 feet of hose (Q = gpm ÷ 100) 
= 0.2 x Q2 per 100' 
= 0.2 x 7.52 x 6 
= 0.2 x 56.25 x 6 
= 11.25 x 6 
= 67.5 psi

Question 6

Appliance Loss

Answer 6

Appliances cause additional resistance to the flow of water, which increases friction loss. To overcome appliance loss in appliances use the following:

Less than 350 gpm – the appliance loss is insignificant so 0 psi will be used in your calculations

Over 350 gpm - 10 psi appliance loss

25 psi loss – ladder pipes

25 psi loss – master streams (except for the mercury monitor)

25 psi – standpipes