Copyright © 2003 Balby International All rights reserved
Hydraulic losses in water supply systems depends in part upon velocity in the pipe and its diametar and roughness of the pipe, and occur along a whole pipe network. Local losses (valves, form losses bend, cross, etc) in long pipe installations are most 10% of linear losses. Head losses are computed according to the DarcyWeisbach equation.. That equation for long pipe installations, where minor losses are 10% of linear losses, is represented as follows:
where:
Δ h is the head losses (pressure
losses
measured as water meters), L is the pipe
length (m), λ is the friction coefficient,
d is the inside pipe diameter (m), V is the flow velocity (m/s), and g is the gravitational
acceleration (m/s”).
In our engineer's usage, we compute
the friction coefficient according to the
equation innovated by professor Georgije Hajdin. This equation is an extension of Blazijus
equation for smooth
pipes and expressed as follows :
where: Re is the Reynolds number and K is the roughness height (mm).
The Reynolds number is computed as:
where:
ν is the kinematic viscosity which amounts n =1.31×
10^{6} m^{2}/s for temperature of 10°
C.
Typical pipe roughness values are shown in the following table. These values will vary depending on the manufacturer, workmanship, age, condition and other factors. For this reason, the following table should be used as a guideline only.
Material 
Pipes condition 
Roughness height K (mm) 
Glass, cooper, bronze, aluminum, plastic 
New made pipes 
0 0.0015 
PE 
New made pipes old pipes 
0.0020.004 
PVC  New made pipes old pipes 
0.0060.012 
Rolled steel  New made pipes, technical smoothed 
0.01 0.05 
Welded and from steel plate 
New made pipes 
0.05 0.10 

Old pipes  started scurf 
0.15 0.2 

Matured scurf 
max 3.0 
Mettle 
New made pipes 
0.05 
Gray cast 
New made pipes, shifted 
0 0.12 

New made pipes, no shifted 
0.15 

Old pipes, started scurf 
max 1.5 

Matured scurf 
max 3 
Asbestos cement 
New made pipes 
0 0.3 
Concrete 
New made pipes, reinforced, smoothed 
0 0.15 

New made pipes, roughed 
0 0.8 

Old pipes, good treated 
0.2 0.3 
A pipeline name