Gas-liquid mixing pumps, also known as dissolved air pumps, are a type of vortex self-priming pump. They create negative pressure inside the pump chamber to suck in gas automatically. Liquid and gas are mixed and pressurized within the pump to dissolve fine bubbles. Typical applications include dissolved air flotation, ozone water production and oxygen-rich water systems.

Core limitation: Standard models support a maximum gas-to-liquid volume ratio of around 1:9, meaning the gas intake cannot exceed 10% by volume. The pump will malfunction if the gas proportion exceeds this value.

1. Define working conditions (the first step for selection)

Liquid flow rate (key parameter)

• Ozone water / oxygen-rich water: Select based on the final outlet flow rate.
• Dissolved air flotation: Do NOT use raw water total flow. Use the recycle dissolved water flow instead, usually 10%–50% of raw water flow. Higher pollutant loads require a larger recycle ratio.

Size the pump for peak flow and add a 10% safety margin. Refer to the manufacturer’s performance curve instead of only relying on nameplate data.

Head calculation

Total head = pipe friction loss + local resistance from valves and elbows + outlet backpressure (pressure inside dissolved air tank). ✅ Reserve an extra 10% safety margin.

Note: Under two-phase gas-liquid operation, the actual pump head is lower than the clean water curve. Do not directly use clean water parameters.

Gas-liquid ratio (common pitfall)

• Standard gas-liquid mixing pump: maximum gas volume fraction ≤10%.
• If higher gas loading is required, ordinary QY series pumps are not suitable; multi-phase pumps should be considered.
• Install a gas flow meter and regulating valve on the gas inlet to stabilize gas intake.

Medium properties

1. Fluid type: clean water, pure water or wastewater? Contains ozone, hydrogen peroxide, acid or alkali? Fine solid particles? A pre-filter is required for media with solids.
2. Temperature: standard models ≤60°C. Mechanical seal material needs upgrading for temperatures above 80°C.
3. Corrosion resistance:
   • Clean water / normal wastewater: 304 stainless steel
   • Ozone or mild corrosion: 316L stainless steel
   • Strong corrosion: FKM seals and special alloys
4. Viscosity: Only applicable for low-viscosity liquids. Not suitable for high-viscosity fluids.

Operation and environment

• Intermittent operation, limited installation space: Direct-coupled type QY(B).
• 24-hour continuous heavy-duty operation, large power: Coupled QYL(B) for longer service life.
• Flammable media or explosion hazardous area: Explosion-proof motor (suffix B).
• Power supply: Single-phase 220V for small flow; three-phase 380V for large flow.

2. Selection of construction and seal

1. Mechanical seal type (mainstream QY): Cost-effective. Use FKM fluororubber seals for ozone service, EPDM for clean water. Risk of leakage exists.
2. Magnetically driven gas-liquid mixing pump: Zero leakage without mechanical seals. Ideal for corrosive and ozone systems where leakage is strictly forbidden, with higher cost.

Ozone rapidly degrades common rubber materials. Seal material is a critical consumable part.

3. Recommended selection for typical applications

1. Ozone water generation: 304 / 316L stainless steel with FKM mechanical seals. Size according to water output and control ozone gas flow.
2. Dissolved air flotation: Size based on recycle flow, 304 stainless steel, matched with pressure gauge and dissolved air tank.
3. Oxygen-rich water: 304 stainless steel with standard rubber seals.
4. Food & beverage: 316L sanitary polished pump body.

4. Common mistakes to avoid

❌ Do not select flotation pumps by raw water total flow; recycle flow is the design basis. ❌ Gas intake cannot exceed 10%. Excessive gas causes heavy vibration, loud noise and unstable outlet flow. ❌ Pipe resistance cannot be ignored. Many projects suffer poor dissolved air effect due to insufficient backpressure even with an oversized pump. ✅ Keep suction piping short with minimum elbows to prevent gas blockage. ✅ Install a pre-filter on the suction side if fine suspended solids exist to protect impeller and mechanical seal.

5. Inquiry checklist to send to manufacturers

1. Application: flotation / ozone water / oxygen-rich water
2. Liquid flow rate: ____ m³/h, required outlet pressure / head (m)
3. Gas type: air / ozone / oxygen, gas flow rate ____ L/min
4. Medium: pH value, temperature, solid content
5. Material requirement, explosion-proof or not, continuous / intermittent operation
6. Installation space, power supply voltage