If you are installing or upgrading a centre pivot system, centre pivot pump sizing matters more than anything else:
Getting the pump size right.
Centre pivot pump sizing is not about guessing. It is about understanding flow, pressure, elevation, and friction — and adding them together correctly.
When the pump is undersized, the pivot struggles to maintain pressure.
When it is oversized, you waste electricity every month.
Let’s break it down step by step in a practical, real-world way.
Step 1: Calculate the Required Flow Rate for Centre Pivot Pump Sizing
The first step in centre pivot pump sizing is determining how much water the system must deliver.
You need:
- Field size (hectares)
- Application depth (mm)
- Irrigation cycle time (hours)
Example:
40 hectares
6 mm application
24-hour rotation
1 hectare = 10,000 m²
6 mm = 6 litres per m²
40 × 10,000 × 6 = 2,400,000 litres
= 2,400 m³ per cycle
2,400 ÷ 24 = 100 m³/h
That means your centre pivot irrigation pump must deliver 100 m³/h continuously.
No rounding down. No estimating.
Step 2: Determine the Required Operating Pressure Centre Pivot Pump Sizing
Most centre pivots operate between:
- 2.5 bar and 4.5 bar
Your sprinkler package will specify the required pressure.
Remember:
1 bar ≈ 10 metres of head
If your pivot requires 3.5 bar:
3.5 × 10 = 35 metres of head
This is already part of your Total Dynamic Head calculation.
Step 3: Add Elevation (Static Head)
Centre pivot pump sizing must include elevation.
Ask:
- How far below the pump is the water level?
- Does the field slope upward?
Example:
Borehole water level = 8 m below pump
Field rises = 6 m
Total elevation = 14 m
Gravity does not negotiate. This number must be included.
Step 4: Calculate Pipeline Friction Loss
Water flowing through pipe creates resistance.
Friction depends on:
- Pipe length
- Pipe diameter
- Flow rate
Example:
180 m pipeline
Friction = 4 m per 100 m
(180 ÷ 100) × 4 = 7.2 m
Add fittings and bends ≈ 2 m
Total friction loss = 9 m
Step 5: Calculate Total Dynamic Head (TDH) for Centre Pivot Pump Sizing
Now we combine everything.
Pivot pressure = 35 m
Elevation = 14 m
Friction = 9 m
Total Dynamic Head (TDH) = 58 metres
Your duty point is:
100 m³/h at 58 metres head
This is the exact requirement for proper centre pivot pump sizing.
Step 6: Select the Pump Correctly
Now review the pump curve.
You want:
- The duty point near the Best Efficiency Point (BEP)
- Not oversized
- Not operating at the extreme right of the curve
Brands like:
- KSB SE & Co. KGaA
- Grundfos
Provide detailed curves to match your required flow and head accurately.
Proper centre pivot pump sizing ensures:
- Stable pressure
- Uniform water distribution
- Lower electricity consumption
- Longer pump life
Common Centre Pivot Pump Sizing Mistakes
Many systems underperform because:
- Elevation was ignored
- Friction was underestimated
- Pressure was guessed
- The pump was oversized “just to be safe”
Oversizing increases your power bill every month.
Undersizing affects crop uniformity.
Neither is profitable.
What Information You Need Before Sizing
Before selecting a centre pivot irrigation pump, collect:
- Field size (hectares)
- Application depth (mm)
- Cycle time
- Required pivot pressure
- End gun pressure
- Water level depth
- Pipe length and diameter
- Elevation differences
With these details, centre pivot pump sizing becomes precise engineering — not trial and error.
Frequently Asked Questions for Centre Pivot Pump Sizing
What is the ideal pressure for a centre pivot system?
Most systems operate between 2.5 and 4.5 bar, depending on the sprinkler package.
How do I calculate TDH for a centre pivot?
Add pivot pressure (converted to metres), elevation, and pipeline friction losses.
Can I oversize my irrigation pump for safety?
Oversizing increases electricity consumption and may reduce system efficiency. Proper sizing is always better.
Final Thoughts
Centre pivot pump sizing is one of the most important decisions in an irrigation project.
When calculated correctly:
- Crops receive uniform application
- Energy costs remain controlled
- Equipment lasts longer
- The system performs consistently
When guessed — problems follow.
If you would like assistance calculating your centre pivot pump sizing correctly, contact our technical team with your system details, and we’ll help you select the right solution.