Module 3 - Hydraulic Calculations Flashcards
Four Principles of Friction Loss
- Varies directly with the length of the hose (double the length = double the friction loss)
- Varies with the square of the velocity (flow) – if we double the flow we will have 4x the FL
- For a given flow, FL varies inversely as the 5th power of the hose diameter
655 /445 = 7
- For the same flow a 44mm hose will have 7x more FL than the 65 - Is dependent on flow and does not change with different pressure
Basic Friction Loss Calculation
FL/L = (Q/100)^2 x C
FL/L = (Q/100)^2 x C
FL/L = FL per length in 30m lengths
Q = quantity of water flowing in L/M
C = coefficient of friction of a given hose
Coefficients
44mm = 6
65mm = 0.8
77mm = 0.4
125mm = 0.03
Determining Friction loss
Two ways: actual test and calculations
Hydraulic Calculation Pump Discharge Pressure
PDP = NP + TFL + APP +/- ELEV
PDP = NP + TFL + APP +/- ELEV
PDP – Pump discharge pressure
NP - nozzle pressure
TFL – total friction loss
APP – appliance pressure loss
ELEV – elevation pressure gain or loss
Nozzle Pressure
solid bore handline – 350 kPa
Fog nozzle handline – 700 kPa
Master stream – 550 kPa
Total Friction loss – different sized lines
TFL = FLa + FLb
Appliance Friction Loss
We consider flow under 1400 lpm to be negligible and consider it to be zero
Flows of 1400 lpm and above simply add 70 kPa to our PDP
Excluding master stream devices
Elevation Equation
Pressure in a column of water is calculated at 10 kPa per meter of elevation
When there is a rise in elevation we need to add to our discharge
When there is a drop in elevation we need to subtract from the discharge pressure
Elevation Change
Commonly found at high rise events
Every floor is 4m – add 40 kPa/floor above ground
We count from the second floor up to the fire floor because we are level with the first floor when pumping
Residential = 3.5m, commercial = 4m
Net Pump Discharge Pressure (NPDP)
Centrifugal pumps can take advantage of incoming water pressure to increase pumping efficiency
If an engine is required to discharge 1000kPa and it has an intake pressure of 350kPa, the pump only needs to add 650kPa more to meet the demand
Nozzle Calculations
Not performed on the fire ground
Too low – limits the flow to less than critical application rate
Too high – may result in unreasonable nozzle reaction
Nozzle Flow (Solid Bore)
L/Min = 0.067 x D^2 NP
Bore Sizes
44mm handline – 24mm
65mm handline – 29mm
Blitzfire solid bore tips – 24mm, 32mm, 38mm
Nozzle Reaction
NR = 0.0015 x D^2 x NP
Configurations of connecting to Hydrants
Single
Twin
Single relay
Twin relay
Two hydrant supply
Single
Twin
Single relay
Twin Relay
Two hydrant supply
Limiting Factors and Solutions
Available water flow from the hydrant/main
The pressure hydrant has to push the water down the supply hose to the truck
Friction loss created by the hose lay supplying the truck
Available water flow from the hydrant/main
Use 125 port as well as a 65 port with a 65 to 125 adapter
Use a second hydrant
The pressure hydrant has to push the water down the supply hose to the truck
Relay supply engine helps maximize the water to the attack engine
Friction loss created by the hose lay supplying the truck
Can be reduced by twinning the supply lines directly from the hydrant or in a relay
*When using a second hydrant, the attack engine compound gauge
must not exceed the original static pressure to prevent pumping back into the water supply*
Hydrant Flow depends on: (S.L.I.P)
- Size
- Length
- Internal condition
- Pressure of the water main
*City of Calgary water services considers hydrant flow of ___________ as a minimum
5000 lpm as a minimum
High rise events
have a standard of 150kpa friction loss and must be added to the calculations
relay operations
boost the pressure to a maximum of 1260 kpa from the supply engine
Max forward lay
of lengths = (discharge-safety) / FL/L
twinning from a single hydrant will increase the flow by
approx. 30%
using two hydrants will yield higher flow than twinning from 1 hydrant
approx. double
useful in areas with low flowing hydrants
