Sodium Hypochlorite Dosing Pump: Selection, Materials and Gas-Locking Fixes
Sodium hypochlorite (10–15% available chlorine) is the most common disinfectant in water and wastewater treatment. It is also one of the hardest chemicals to dose reliably: it corrodes metals, crystallises when it dries, and releases gas that stops pumps from priming.
Dosing hypochlorite? Send us the flow and pressure for a quote.
Which pump type
A diaphragm metering pump is the standard choice. The diaphragm keeps the chemical sealed from the drive, so there is no packing leak of a corrosive, smelly liquid. Plunger pumps are not recommended for hypochlorite.
Materials of construction
| Part | Recommended | Avoid |
|---|---|---|
| Pump head | PVDF or PP | SS304, SS316, Alloy 20 |
| Diaphragm | PTFE-faced | Plain rubber |
| Valve balls | Ceramic or PTFE | Stainless steel |
| Seals / O-rings | Viton (FKM) or PTFE | Nitrile |
| Tubing | PVC, PE or PVDF | Metal pipe |
More chemicals are rated in our chemical compatibility chart.
Why hypochlorite pumps lose prime (gas locking)
Hypochlorite slowly breaks down and releases oxygen gas, especially when warm or exposed to sunlight. Gas bubbles collect in the pump head; the diaphragm then compresses gas instead of liquid and the pump stops delivering.
Fixes that work
- Flooded suction: place the tank above the pump so chemical flows in by gravity.
- Short, straight suction line with no high points where gas can collect.
- Degassing (bleed) valve on the pump head, returning to the tank.
- Keep it cool: shade the tank and pump; heat speeds up decomposition.
- Run the pump at a higher stroke length and lower speed rather than very short strokes.
- Fresh chemical: buy in quantities you use within a few weeks.
Sizing example
A 200 m³/h water plant dosing 3 ppm chlorine with 12% hypochlorite (density 1.2) needs 200 × 3 ÷ (12 × 10 × 1.2) ≈ 4.2 L/h. Choose a pump of about 6 LPH so it runs near 70% stroke. Try your own numbers in the dosing pump calculator.
Maintenance
Flush the head with water before long stops so crystals do not form on the valves, inspect valve balls and seats every few months, and replace the diaphragm as per running hours. Our AMC covers this for plants that want it done for them.
Frequently asked questions
Can I use a stainless steel pump for sodium hypochlorite?
No. Hypochlorite causes pitting and corrosion in SS304 and SS316. Use PVDF or PP liquid ends.
Why does my hypochlorite pump work in the morning but fail in the afternoon?
Higher afternoon temperatures increase gas release. Shade the tank and pump, flood the suction and fit a degassing valve.
How often should a hypochlorite pump diaphragm be replaced?
It depends on pressure, temperature and running hours. Inspect it at every service; many plants change it yearly as preventive maintenance.
Get a hypochlorite dosing pump sized for your plant.
Jagdish Engineering Works, Mumbai – manufacturer of plunger and diaphragm metering pumps and pressure relief valves since 1969. Our engineers design, test and repair dosing pumps for water treatment, chemical, refinery, fertilizer, sugar and paper plants.
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