Pump Head & Flow Rate Calculator
Calculate Total Dynamic Head (TDH) based on system geometry and flow requirements.
Vertical distance from water level to discharge point.
Total length of pipe run including fittings allowance.
Internal diameter of the pipe.
Volume of water required per minute.
PVC / Plastic (Smooth) – C=150
Copper / Brass – C=140
Cast Iron (New) – C=130
Galvanized Steel – C=100
Old Steel / Corroded – C=80
Affects friction loss (Roughness Coefficient).
Fluid Velocity:
– m/s
Friction Head Loss:
– m
Total Dynamic Head (TDH):
– m
System Pressure Required:
– bar
How to Calculate Pump Head and Flow Rate
Selecting the right pump requires understanding two critical metrics: Flow Rate (how much water you need) and Total Dynamic Head (TDH) (how much pressure is needed to push that water). This calculator helps you determine the required TDH so you can reference a pump curve chart and select the correct equipment.
Understanding the Variables
- Static Head: The vertical height difference between the source water surface and the highest point of discharge. Gravity is the main force to overcome here.
- Friction Head Loss: As water flows through a pipe, friction against the pipe walls slows it down. This creates "virtual" height (or head) that the pump must overcome. Smaller pipes and higher flow rates increase friction significantly.
- Total Dynamic Head (TDH): This is the sum of Static Head + Friction Head + Operating Pressure (if any). It represents the total work the pump must do.
Formulas Used
This calculator utilizes the Hazen-Williams equation to determine friction loss, which is standard for water distribution systems:
$$ h_f = \frac{10.67 \cdot L \cdot Q^{1.852}}{C^{1.852} \cdot d^{4.87}} $$
Where:
- hf = Head loss due to friction (meters)
- L = Length of pipe (meters)
- Q = Flow rate (cubic meters per second)
- C = Roughness coefficient (depends on pipe material)
- d = Pipe inner diameter (meters)
Why Velocity Matters
The calculator also outputs Fluid Velocity. Generally, you should aim for a velocity between 1.5 m/s and 2.5 m/s. If velocity is too high (> 3 m/s), you risk water hammer, noise, and excessive friction loss. If it is too low, you may allow sediment to settle in the pipes.
Step-by-Step Calculation Example
- Determine Geometry: Measure the vertical rise (Static Head) from the water level to the tank inlet. Let's say it is 15 meters.
- Measure Run: Measure the total length of the pipe. Let's say it is 100 meters.
- Define Needs: You need 120 Liters/minute (flow rate).
- Check Friction: Using a 50mm PVC pipe, the friction loss might be calculated as roughly 3.5 meters.
- Calculate TDH: 15m (Static) + 3.5m (Friction) = 18.5m Total Dynamic Head.
- Select Pump: Look for a pump that provides 120 L/min at 18.5m head on its performance curve.