How to Select and Size a Metering Pump: Complete Guide

Selecting the right metering pump is critical for accurate chemical dosing in water treatment, wastewater, cooling towers, and industrial processes. A poorly sized pump leads to overdosing, underdosing, wasted chemicals, or equipment failure.

This guide walks you through the key factors engineers and operators use to choose and size a metering pump.

1. Define Your Required Flow Rate

The most important parameter is the required dosing flow rate (l/h or gph).

Calculate it based on:

• Process flow rate (m³/h)
• Target chemical concentration (mg/L or ppm)
• Chemical strength/concentration (%)

Example formula: Required flow (l/h) = (Process flow × Target concentration × 100) / (Chemical concentration × 1000)

Always add a safety margin of 10–20% for peak demand and future expansion.

2. Determine Operating Pressure

Metering pumps must overcome the system back pressure (pipeline pressure + injection point pressure + friction losses).

• Solenoid diaphragm pumps: typically up to 10–16 bar
• Motor-driven pumps: higher pressures available
• Peristaltic pumps: usually lower pressure (up to 4–7 bar)

Select a pump whose maximum pressure rating is at least 20% higher than your normal operating pressure.

3. Choose Pump Type

| Pump Type | Best For | Advantages | Limitations | |-----------|----------|------------|-------------| | Solenoid Diaphragm | Low to medium flow, precise dosing | Accurate, low maintenance, no rotating parts | Limited max flow (~80 l/h) | | Motor-Driven Diaphragm | Medium to high flow | Higher capacity, continuous duty | Higher cost, more maintenance | | Peristaltic | Viscous, abrasive, or shear-sensitive fluids | Excellent for dirty fluids, easy tube change | Lower pressure, tube wear |

4. Select Liquid-End Materials

Match materials to the chemical being dosed:

• PVC / PVDF: most acids, alkalis, sodium hypochlorite
• PTFE / PVDF: aggressive chemicals
• Stainless Steel 316L: clean chemicals, higher temperature
• EPDM / FKM (Viton) seals: check chemical compatibility chart

Always verify with the chemical supplier’s compatibility data.

5. Accuracy and Turndown Ratio

• Standard accuracy: ±2% or better
• High-precision applications (e.g., pH control): look for ±1%
• Turndown ratio: higher is better (1:1000 on some digital pumps) for flexible operation

6. Control Method

Choose based on your automation needs:

• Manual stroke length + frequency
• External pulse or 4–20 mA
• Flow-proportional dosing
• Timer / batch mode
• Integration with online analyzers (pH, ORP, residual chlorine)

7. Additional Considerations

• Suction lift capability (especially for viscous chemicals)
• Degassing function for sodium hypochlorite
• Level switch or low-level alarm
• Power supply (110V / 220V, single phase)
• IP rating for outdoor or wet locations
• Spare parts availability and local service

Summary Checklist

Before requesting a quote, prepare:

1. Required flow rate (min / normal / max)
2. Operating pressure
3. Chemical name and concentration
4. Preferred control method
5. Installation location (indoor/outdoor, temperature)

Providing these details allows us to recommend the most suitable and cost-effective metering pump for your application.

Need help with a specific project? Contact our technical team with your process parameters.