i. Glossary
Term | Description | Units |
a | Acceleration | Metres/Second2 |
A | Area | Metres2 |
At | Reservoir Supply Pipe Area | Metres2 |
D,d | Pipe Diameter | Metres/inches |
E | Energy | Joules |
Ek | Kinetic Energy | Joules |
Ep | Potential Energy | Joules |
F | Force | Newtons |
f | Friction Factor | – |
fA-n | Frictional Head Loss in Tap Supply Pipe | Metres |
fh | Frictional Head Loss | Metres |
fhl | Frictional Head Loss in Larger Diameter Pipe | Metres |
fhn | Frictional Head Loss in Pipe n | Metres |
fhs | Frictional Head Loss in Smaller Diameter Pipe | Metres |
fp | Frictional Loss (Pressure) | Newtons/Metre2 |
ft-A | Frictional Head Loss in Reservoir Supply Pipe | Metres |
g | Gravitational Acceleration | Metres/Second2 |
h | Height | Metres |
H | Desired Frictional Head Loss | Metres |
hA | Height of Junction A | Metres |
HA | Head at Point A | Metres |
hB | Height of Junction B | Metres |
Hmax | Maiximum Static Head | Metres |
hn | Height of nth Tap | Metres |
Hn | Residual Head at Tap n | Metres |
ht | Reservoir Height | Metres |
I | Electrical Current | Amps |
L | Length | Metres |
Ln | nth Tap Supply Pipe Length | Metres |
Lt | Reservoir Supply Pipe Length | Metres |
M | Mass | Kilogrammes |
n | Number of Taps | – |
NRE | Reynolds Number | – |
P | Pressure | Newtons/Metre2 |
PA | Pressure at Junction A | Newtons/Metre2 |
PB | Pressure at Junction B | Newtons/Metre2 |
Pk | Kinetic Energy as a Pressure | Newtons/Metre2 |
Pn | Residual Pressure at nth tap | Newtons/Metre2 |
Pp | Pump Pressure | Newtons/Metre2 |
Pp | Potential Energy as a Pressure | Newtons/Metre2 |
Pt | Turbine Pressure | Newtons/Metre2 |
Q,q | Volumetric Flow Rate | Metre3/Second |
qA | Volumetric Flow Rate at Junction A | Metre3/Second |
S | Distance | Metres |
t | Time | Seconds |
v | Velocity | Metres/second |
V | Volume | Metre3 |
V | Voltage | Volts |
vA | Velocity of Water in Reservoir Supply Pipe | Metres/Second |
vav | Average Velocity | Metres/Second |
vn | Velocity of Water in nth Tap Supply Pipe | Metres/Second |
W | Power | Watts |
We | Electrical Power | Watts |
Win | Power Supplied to Pump | Watts |
Wout | Power Supplied by Pump | Watts |
Δh | Total Difference in Head between Tanks | Metres |
ΔH | Residual Head | Metres |
ΔP | Residual Pressure | Newtons/Metre2 |
γ | Pump Efficiency | – |
μ | Kinematic Viscosity | Metres 2/Second |
ρ | Density (ro) | Kilogrammes/Metre3 |
ii. Scope
This manual is intended to aid the water projects worker or volunteer in the following ways :
- To explain, from first principals and using basic physical relations, the origin of the equations that design water systems.
- To systematically outline the key equations and explain how to apply them to scenarios where there is no text book method readily available.
- To give step by step numerical solutions to some of the more common and also some special scenarios.
- To systematically lay down the design parameters for gravity flow water systems and show how they should be applied to a design.
Sections 2-7 explain the basic concepts, show how the core equations are derived, explain perfect and imperfect systems and cover the analysis of pumps and turbines.
Sections 8 and 9 show how to apply the core equations to a series of common and special scenarios.
The worked examples 1-8 show how to simplify the equations developed in Sections 8 and 9 for practical use and give step by step numerical examples for each scenario. In addition worked example 9 shows the design process applied to a sample gravity flow water system design.
Appendices 1-6 give more complex derivations of the core relations, explanations of useful processes in the calculations and additional technical data.
For the experienced water system designer I would suggest reading through Sections 8 and 9, Appendix 4 and Worked Example 9 in particular.
Any questions about this manual should be addressed to Dodger at dodger@irational.org.
iii. References
- A Handbook of Gravity-Flow Water Systems : Thomas D.Jordan Jnr. : Intermediate Technology Publications 1996.
- Basic Engineering Sciences and Structural Engineering for Engineer-in-Training Examinations : Apfelbaum & Ottesen : Hayden Book Company 1970.
- Friction Loss Characteristics Chart : Polyethylene (PE) SDR-Pressure Rated Tube : PISTA & Gustavo Urbano.
iv. Notes
- In the numerical calculations for the Worked Examples, the asterisk (*) denotes the multiplication sign and the slash (/) the divide sign.
- In general, metric fundamental units (Metres, Kilogrammes and Seconds) have been used in the Worked Examples, the two main exceptions being inches for pipe diameters and Litres/Second (LPS) for flow rates.