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How can i find the relative roughness of fire hose?
- Thread starter mrChikai
- Start date
Search for the NFPA document "determination of fire hose friction loss characteristics"
The fire fighting industry uses a slightly different approach to calculating pressure drops from that used by process and mechanical engineers. I re-jigged the data from page C-6 of the referenced article to work out that the average roughnesses were between 0.02 and 0.05 mm. For typical fire hose sizes this variation makes very little difference to the calculated pressure drop and for my AioFlo program I have used 0.05 mm.
Note that these values do not apply to spiral reinforced hoses which have a bellows like internal surface.
Katmar Software - AioFlo Pipe Hydraulics
"An undefined problem has an infinite number of solutions"
The fire fighting industry uses a slightly different approach to calculating pressure drops from that used by process and mechanical engineers. I re-jigged the data from page C-6 of the referenced article to work out that the average roughnesses were between 0.02 and 0.05 mm. For typical fire hose sizes this variation makes very little difference to the calculated pressure drop and for my AioFlo program I have used 0.05 mm.
Note that these values do not apply to spiral reinforced hoses which have a bellows like internal surface.
Katmar Software - AioFlo Pipe Hydraulics
"An undefined problem has an infinite number of solutions"
- Thread starter
- #3
Thanks Katmar!
im trying to calculate the pressure drop with regards to the distance covered with a specific hose diameter(3 inch),
and im using the equation
head loss(hl) = (fl(v^2))/2Dg
and then used p= (rho*g*hl)
*
I've used f as 0.017
is this a right approach?
secondly I've checked on web, and ive found this formula.
check it out!
which approach is much more accurate?
im trying to calculate the pressure drop with regards to the distance covered with a specific hose diameter(3 inch),
and im using the equation
head loss(hl) = (fl(v^2))/2Dg
and then used p= (rho*g*hl)
*
I've used f as 0.017
is this a right approach?
secondly I've checked on web, and ive found this formula.
check it out!
which approach is much more accurate?
The equation you found for hl is what is known as the Darcy-Weisbach equation. The equation shown on the Fire Engine Academy page is a simplified specific version of the Hazen-Williams Equation. The Darcy-Weisbach equation is generally regarded as a more accurate and versatile equation, but if you are working with water and you have the correct Friction Loss Coefficients the Hazen-Williams is acceptably accurate.
Because Hazen-Williams is easier to use, and has been around longer, it seems to be the equation recommended (or even mandated) by fire protection authorites world-wide. I don't do a lot of fire water work, but when I do I use Darcy-Weisbach to be sure that I have got the correct pipe sizes or flow rates, and then I re-run the calcs with Hazen-Williams to satisfy the authorities.
Katmar Software - AioFlo Pipe Hydraulics
"An undefined problem has an infinite number of solutions"
Because Hazen-Williams is easier to use, and has been around longer, it seems to be the equation recommended (or even mandated) by fire protection authorites world-wide. I don't do a lot of fire water work, but when I do I use Darcy-Weisbach to be sure that I have got the correct pipe sizes or flow rates, and then I re-run the calcs with Hazen-Williams to satisfy the authorities.
Katmar Software - AioFlo Pipe Hydraulics
"An undefined problem has an infinite number of solutions"
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