2.54 m of head is lost over 150 m of pipe (1.69 m per 100 m), 8.5% of the gross head, leaving 27.5 m net. A velocity of 1.91 m/s is within the usual 1–3 m/s range. The smallest inner diameter that keeps losses below 10% is 194 mm.
Total head loss
2.54m
8.5% of gross head
Net head
27.5m
from 30 m gross
Friction loss (Darcy)
2.07m
minor losses 0.46 m
Flow velocity
1.91m/s
velocity head 0.186 m
Reynolds number
293,849
turbulent
Friction factor f
0.0149
Colebrook · Swamee–Jain 0.0148
Hazen–Williams check
2.53m
C = 150 · Swamee–Jain 2.53 m
Power at turbine
11.3kW
1 kW lost to the pipe
Min. diameter for target
194mm
≤ 10% loss
Water-hammer surge
12m
Michaud (slow closure) · wave 300 m/s, 2L/a = 1 s
Max static + surge pressure
4.1bar
choose pipe pressure class above this
Diameter options
| Inner Ø (mm) | Velocity (m/s) | Head loss (m) | Loss % | Net head (m) | Power (kW) |
|---|---|---|---|---|---|
| 97 | 8.12 | 79.94 | 100% | 0 | 0 |
| 109 | 6.43 | 45.5 | 100% | 0 | 0 |
| 122 | 5.13 | 26.48 | 88.3% | 3.5 | 1.5 |
| 137 | 4.07 | 15.21 | 50.7% | 14.8 | 6.1 |
| 153 | 3.26 | 8.99 | 30% | 21 | 8.7 |
| 172 | 2.58 | 5.17 | 17.2% | 24.8 | 10.2 |
| 193 | 2.05 | 3 | 10% | 27 | 11.1 |
| 217 | 1.62 | 1.73 | 5.8% | 28.3 | 11.6 |
| 243 | 1.29 | 1.02 | 3.4% | 29 | 11.9 |
| 273 | 1.03 | 0.59 | 2% | 29.4 | 12.1 |
| 306 | 0.82 | 0.35 | 1.2% | 29.7 | 12.2 |
| 343 | 0.65 | 0.21 | 0.7% | 29.8 | 12.3 |
| 385 | 0.52 | 0.12 | 0.4% | 29.9 | 12.3 |
Pipe material reference
| Material | Roughness ε (mm) | Hazen–Williams C | Wave speed (m/s) | Loss for your pipe (m) |
|---|---|---|---|---|
| HDPE / PE100 | 0.007 | 150 | 300 | 2.54 |
| PVC-U | 0.0015 | 150 | 400 | 2.5 |
| GRP / fibreglass | 0.01 | 145 | 500 | 2.56 |
| Steel, new welded | 0.045 | 130 | 1,100 | 2.76 |
| Steel, old / rusty | 0.5 | 100 | 1,100 | 4.01 |
| Galvanised steel | 0.15 | 120 | 1,100 | 3.19 |
| Ductile iron, cement-lined | 0.03 | 140 | 1,150 | 2.68 |
| Cast iron, unlined | 0.26 | 100 | 1,100 | 3.5 |
| Concrete (smooth–average) | 0.6 | 120 | 1,000 | 4.18 |
| Riveted steel | 2 | 95 | 1,000 | 5.78 |
- Roughness values are typical for new pipe. Scale, biofilm and corrosion raise ε over time, and old steel can lose twice as much head as new.
- Hazen–Williams is empirical and holds only for water in turbulent flow at normal temperatures. Darcy–Weisbach with Colebrook is the reference method.
- The water-hammer estimate uses a typical pressure-wave speed for the material; the real speed depends on wall thickness and pipe class. On large schemes, size surge protection with a transient analysis.