Copyright © 2015 www.balby.com All rights reserved.
IMPORTANT !!!!
THE COMPUTER SOFTWARE FOR COMPUTATION HEAD LOSSES IN WATER SUPPLY SYSTEMS ACCORDING DARCY  WEISBAH FORMULA
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).
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 
The Reynolds number is computed as:
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 :
For a hydraulic resistance computation in water supply penstocks necessity is enter next attributes of pipes in indicated gauge units.
Internal pipe diametar  d  mm  
Roughness height  K  mm  
Assumed flow  Q  l/s  
Pipe length  L  m  


Crosssectional area of a pipe  F  m2  
Flow velocity through a pipe  v  m/s  
Reynolds number  Re  
Friction coefficient  l  
Hhydraulic head losses (head losses in water meters)  D h  m 