How to Select a Borehole Pump?

Selecting the correct borehole pump is crucial for efficient and reliable water supply, involving a detailed assessment of your water requirements, the specific characteristics of your borehole, and your available power infrastructure.

Key Factors for Borehole Pump Selection

To make an informed decision, consider the following essential factors:

1. Determine Your Water Requirements

Understanding how much water you need and at what pressure is the foundational step.

• Flow Rate: Calculate your estimated daily or hourly water consumption. This includes:
  • Household use (drinking, bathing, cleaning, toilets)
  • Irrigation (garden, crops)
  • Livestock watering
  • Other specific needs (e.g., filling a pool)
  • Measurement: Typically expressed in litres per minute (LPM) or gallons per minute (GPM).
• Pressure: Define the required pressure at the points of use (e.g., showers, sprinklers, taps).
  • Measurement: Usually measured in Bars or Pounds per Square Inch (PSI). Adequate pressure ensures comfortable water delivery and efficient operation of appliances.

2. Understand Borehole Specifications (Total Dynamic Head - TDH)

The physical attributes of your borehole are paramount for determining the necessary pump power and lift capability. The most critical calculation here is the Total Dynamic Head (TDH), which represents the total vertical distance the pump must lift water, plus any pressure losses.

• Static Water Level: The depth from the ground surface to the water level when the pump is not running.
• Pumping Water Level (Drawdown): The depth from the ground surface to the water level when the pump is operating. The difference between static and pumping levels is the drawdown.
• Borehole Depth & Diameter: The overall depth determines how far down the pump can be placed, and the diameter dictates the maximum pump size you can install.
• Pipe Friction Loss: Energy lost due to friction as water moves through pipes, fittings, and valves. This increases with pipe length, smaller diameter, and higher flow rates.
• Elevation Difference: The vertical height from the borehole's discharge point to the highest point where water is delivered.
• Required Delivery Pressure: Convert the desired delivery pressure into an equivalent head (e.g., 1 Bar ≈ 10 metres of head).

TDH Calculation Formula:
TDH = (Pumping Water Level - Ground Level) + (Elevation to Discharge Point) + (Pipe Friction Loss) + (Required Delivery Pressure Head)

3. Assess Available Power Source

This is a fundamental consideration that dictates the type and size of pump motor you can use.

The first and most basic factor to consider when selecting a borehole pump is to determine the available power source: 220V Single phase or 380V Three phase.

• 220V Single Phase: This is typically found in residential and smaller commercial settings. Pumps designed for single-phase power are suitable for most domestic applications and smaller irrigation systems. They are generally less powerful than three-phase pumps.
• 380V Three Phase: Common in agricultural, industrial, and larger commercial applications, three-phase power enables the use of more powerful and efficient pumps. If you intend to use a 380V 3Phase pump, make sure that your 380V three-phase power source has three live lines, a neutral line, and an earth available. Proper wiring is critical for safe and efficient operation.
• Alternative Power Sources: Consider solar pumps for off-grid locations or areas with unreliable grid power. Ensure the pump is compatible with backup generators if required.

4. Pump Type and Material Considerations

• Submersible Pumps: These are the most common choice for boreholes. They are designed to be fully submerged in the water, which helps in cooling the motor, reduces noise, and pushes water up efficiently.
• Pump Material: For longevity, especially with varying water quality, opt for pumps made from corrosion-resistant materials like stainless steel. This prevents degradation and contamination of your water supply.

5. Borehole Yield

It's vital to know your borehole's sustainable yield – the maximum rate at which water can be continuously extracted without depleting the aquifer. Your chosen pump's flow rate should never exceed the borehole's yield to prevent dry running, which can severely damage the pump. A professional borehole driller or hydrogeologist can perform a yield test.

Practical Steps for Selecting Your Borehole Pump

1. Gather Data: Collect all necessary information: water usage, borehole depth, static and pumping water levels, diameter, and power supply details.
2. Calculate TDH and Required Flow: Use the data to accurately calculate your Total Dynamic Head and required flow rate.
3. Consult Pump Curves: With your calculated TDH and flow rate, consult pump performance curves (charts provided by manufacturers). These charts show a pump's efficiency at various flow rates and heads. Find a pump that operates within its most efficient range for your specific TDH and flow.
4. Consider Pump Protection: Invest in protection devices like dry-run protection (to prevent damage if the water level drops too low), overload protection, and surge protection.
5. Seek Professional Advice: For complex installations or if unsure, consult with a qualified pump specialist or hydrogeologist. They can help with precise calculations, recommend suitable models, and ensure proper installation.

Important Considerations

• Cable Sizing: Ensure the electrical cable connecting the pump to the power source is correctly sized for the pump's power and the depth of installation to prevent voltage drop and overheating.
• Control Box: Most single-phase submersible pumps require a control box (also known as a starter box) for starting and protecting the motor.
• Installation: Professional installation is highly recommended to ensure the pump is correctly positioned, wired, and protected, maximizing its lifespan and efficiency.

By carefully evaluating these factors, you can select a borehole pump that reliably meets your water demands and provides long-term, efficient service.