Dosing pump calculator: chemical flow in LPH
How the calculation works
Mass of active chemical needed per hour (g/h) = flow (m³/h) × dose (g/m³, same as ppm). Divide by the strength (as a fraction) to get grams of solution per hour, then by density (×1000) to get litres per hour. A metering pump is most accurate between about 10% and 100% of its stroke, so leave headroom for future demand and dose changes.
Typical doses
| Application | Chemical | Typical dose |
|---|---|---|
| Drinking water disinfection | Sodium hypochlorite | 1–5 ppm as Cl₂ |
| Coagulation | Alum / PAC | 10–50 ppm |
| Flocculation | Polyelectrolyte | 0.5–2 ppm |
| RO antiscalant | Antiscalant | 2–5 ppm |
| Boiler oxygen scavenging | Sodium sulphite | as per O₂ level |
Doses vary with water quality; confirm with your chemical supplier.
Questions
How do I calculate dosing pump capacity?
Chemical flow in L/h = process flow (m³/h) × dose (ppm) ÷ (chemical strength % × 10 × density in kg/L). Then select a pump rated about 30–40% higher than this flow.
What is ppm in chemical dosing?
ppm (parts per million) in water treatment means milligrams of active chemical per litre of water, which is the same as grams per cubic metre.
Why should a dosing pump be oversized?
Metering pumps are most accurate in the middle of their stroke range. Sizing about 30–40% above the calculated flow keeps the pump at 60–80% stroke and leaves room for higher doses.
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