We have reached the final part of the water piping system design calculation example tutorial. We will use most of the data calculated so far (refer Part-1 to Part-7) as input for the D’Arcy-Weisbach pressure loss equation. From this equation we will know the actual pressure or head loss in the pipe system. Then we will check whether the actual pressure drop in pipe is less than the already calculated permitted pressure loss in the piping system.
Darcy–Weisbach Equation for pressure head loss can be expressed as:
Δh = λ*(l/dh)*(v2/2*g)…………………………….Eq.1
Δh – Pressure head loss for the piping system
λ – Moody friction factor
l – Effective pipe length
dh – Hydraulic diameter
v – Velocity of the fluid
g – Gravitational acceleration (9.81 m/s2)
Getting Back to our problem:
For using the D’Arcy Weisbach formula (Eq.1) for our water piping system example, we have the following inputs:
λ = Moody friction factor = 0.035 (refer part-7)
l = Effective pipe length = 22 meter (refer part-2)
dh = Hydraulic diameter = 0.02 meter (refer part-4)
v = Velocity of the fluid = 1.591 m/s (refer part-6)
g = Gravitational acceleration (9.81 m/s2)
By inputting the above values to the Eq.1, we will get the total head loss for our case as
Δh = 4.96 meter
Pressure head drop per unit length of pipe = Δh / l = 4.96/22 = 0.225 meter of head per meter of pipe run.
Now refer the permissible head loss calculation of Part-3 and you will find that permissible value for our case is 0.22 meter of head per meter of pipe run.
So, we can conclude that the pipe diameter of 20 mm, we assumed at the beginning of this tutorial, is safe for the water piping system problem considered for this tutorial.
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