What is the Layne Equation and Why Should You Care?
The Layne Equation is a specialized formula used in well and pump applications, derived from the Hazen-Williams equation for water flow in pipes. It's particularly useful for engineers and technicians working with water systems, wells, and pumping applications.
Understanding this equation helps you analyze pipe flow characteristics, determine appropriate pipe sizes, and troubleshoot system performance issues. Whether you're designing a new water system or evaluating an existing one, the Layne equation provides valuable insights.
How to Calculate with the Layne Equation
The Layne equation relates flow rate, head loss, pipe dimensions, and the pipe roughness coefficient:
[C = \frac{Q \times D^{2.63}}{H \times L^{0.54}}]
Where:
- C is the Hazen-Williams roughness coefficient
- Q is the flow rate in gallons per minute (gpm)
- D is the pipe diameter in inches
- H is the head loss in feet
- L is the pipe length in feet
Calculation Example
Given:
- Flow Rate (Q): 100 gpm
- Head Loss (H): 5 ft
- Pipe Length (L): 100 ft
- Pipe Diameter (D): 4 inches
Calculate:
[C = \frac{100 \times 4^{2.63}}{5 \times 100^{0.54}}]
[C = \frac{100 \times 32.22}{5 \times 12.02}]
[C = \frac{3222}{60.1} \approx 53.6]
Common C Factor Values
| Pipe Material | Typical C Value |
|---|---|
| New plastic (PVC, HDPE) | 150 |
| New steel | 140 |
| Cast iron (new) | 130 |
| Cast iron (10 years) | 110 |
| Cast iron (20+ years) | 80-100 |
A lower calculated C value than expected may indicate scaling, corrosion, or buildup inside the pipe.