Dosing of liquids

Practical design and component selection for liquid dosing in water treatment

The dosing of chemicals is one of the central tasks in water treatment – whether in the municipal sector, in industry or in swimming pools. Despite many years of use, there are numerous challenges in the correct design and configuration of dosing systems. This article provides a practical approach and a concrete example of implementation.

1. Approach to designing a dosing system

1.1 Collect basic data

• Dosing agent / active ingredient content of the agent
• Required dosing quantity (e.g. in mg/l)
• Temperature at the injection point
• Materials in the dosing circuit / at the injection point
• Pressure conditions at the dosing point
• Amount of water to be treated per hour

1.2 System-specific parameters

• Control of the dosing pump (e.g. water meter, time control)
• Dosing agent extraction (e.g. from canister or storage tank)
• Properties of the dosing agent (viscosity, density, degassing behaviour)

1.3 Accessories and measurement technology

• Measuring devices for concentration control (e.g. photometers)
• Barrel transfer pumps
• Personal protective equipment (PPE)

2. Example: Water meter-controlled dosing system

2.1 Given initial data

• Dosing agent: Duochlorin (sodium hypochlorite, 19%)
• Density: 1.22 g/cm³
• Required dosage: 0.3 mg/l sodium hypochlorite
• Water volume: 100 m³/h
• Water meter control: 100 l/pulse
• Length of dosing line: 12 m
• Dosing tank: 45 l
• Selected dosing pump capacity: 0.7 l/h

2.2 Calculation of the dosing quantity

Step 1: Conversion of the required dosage:
0.3 mg/l / (1.22 g/cm³ × 1000) = 0.0002459 ml/l

Step 2: Dosage amount per pulse:
0.0002459 ml/l × 100 l/pulse = 0.02459 ml/pulse

The required delivery rate is therefore minimal. A pump with a delivery rate of 0.7 l/h offers sufficient control reserve.

2.3 Recommended components

• Dosing pump 0.7 l/h
• Dosing container 45 l
• Suction set with dry-run protection
• 12 m PVC dosing hose (perlon-reinforced, 6/12 mm)
• Pulsation damper
• Barrel transfer pump
• 1 canister of Duochlorin
• Activated carbon filter on the vent
• Personal protective equipment (e.g. gloves, safety goggles)
• Photometer for checking concentration

3. Conclusion

The correct design of a dosing system requires careful recording of all chemical, hydraulic and control parameters. Due to the large number of possible combinations and material- and chemical-related special features, experience in system configuration is essential. Whether for swimming pools, drinking water plants, boiler rooms or industrial applications – we are happy to support you in planning and implementing your optimal dosing solution.