How to Clean Large-Flow Filters

1. Pre-Cleaning Judgment: Is Cleaning Feasible?

First evaluate whether the filter is suitable for cleaning to avoid unnecessary operations:

1. Cleaning-Friendly Conditions

• Contamination Type: Inorganic pollutants (e.g., sand, sediment, metal particles) with low adhesion—easy to remove via physical methods.
• Filter Condition: No visible damage (e.g., cracks, media shedding, seal deformation); filter material is water-resistant/chemical-resistant (e.g., PTFE, glass fiber, reinforced PP).
• Contamination Degree: Early-stage clogging (pressure drop 0.08-0.12MPa, not exceeding 0.15MPa threshold); no deep penetration of pollutants into the filter media.

2. Non-Cleaning Scenarios (Replace Immediately)

• Pollutant Characteristics: Adhesive organic matter (e.g., oil sludge, biological slime), corrosive substances, or polymerized residues—difficult to remove and prone to media adsorption.
• Filter Damage: Visible cracks, media collapse, or seal aging (risk of unfiltered water bypass after cleaning).
• Over-Pollution: Pressure drop exceeds 0.15MPa, or flow rate drops below 70% of rated value (pollutants have penetrated the media layer).
• Disposable Design: Standard PP melt-blown or non-backwashable pleated filters (cleaning may destroy their gradient filtration structure).

1. Common Cleaning Methods (Select Based on Contamination and Material)
2. Backwash (Physical Cleaning) – Most Widely Used

Suitable for: Inorganic particle contamination (sand, sediment) in water-based systems; backwashable large-flow filters (with dedicated backwash ports).

Principles

Reverse the flow direction (from outside to inside) to flush out surface and shallow-layer pollutants, restoring partial flux.

Operating Steps

1. System Preparation: Close the filter’s inlet/outlet valves, relieve pressure to 0MPa, and isolate the filter from the main system.
2. Connect Backwash Pipeline: Connect the backwash water source (clean water with pressure 0.1-0.2MPa higher than the filter’s operating pressure) to the filter’s outlet (backwash inlet), and connect the drain pipe to the inlet (backwash outlet).
3. Backwash Operation:
• Open the backwash valve and drain valve, controlling the flow rate to 1.2-1.5 times the normal operating flow (avoid excessive pressure damaging the media).
• Maintain backwash for 5-10 minutes, or until the drained water is clear (no visible particles).
4. Rinse: Switch back to normal flow direction, flush the filter with clean water for 2-3 minutes to remove residual pollutants, then close the drain valve.
5. Pressure Test: Reinstall the filter, gradually restore system pressure, and check for leaks and pressure drop (normal initial pressure drop ≤0.05MPa).

2. Chemical Cleaning – For Stubborn Contamination

Suitable for: Oil contamination, biological slime, or scale; filters made of chemical-resistant materials (PTFE, glass fiber, 316L stainless steel frameworks).

Key Notes

• Avoid incompatible chemicals (e.g., strong acids for PP filters, oxidizers for nylon filters).
• Pre-test chemical concentration on a small area to prevent media damage.

Common Chemical Agents and Applications

Operating Steps

1. Pre-Rinse: Use clean water to flush the filter surface to remove loose particles (reducing chemical usage).
2. Chemical Preparation: Prepare the cleaning solution according to the table above, ensuring uniform mixing.
3. Soaking/Circulating:
• Soaking method: Immerse the entire filter in the cleaning solution (ensure full submersion) for the specified time; agitate gently every 10 minutes to enhance cleaning.
• Circulation method: Connect a circulating pump to the filter, circulate the cleaning solution at 5-10m³/h for 20-40 minutes (more effective for deep contamination).
4. Neutralization and Rinsing:
• After chemical cleaning, rinse the filter with clean water until the effluent is neutral (pH 6-8).
• For acid-cleaned filters, rinse with a 0.5% sodium bicarbonate solution first, then with clean water (to avoid residual acid corrosion).
5. Drying and Inspection: Air-dry the filter in a clean, ventilated environment (avoid direct sunlight); check for media damage or residual contamination before reinstallation.

3. Ultrasonic Cleaning – For Precision Filter Media

Suitable for: Fine particle contamination in precision filters (1-5μm) made of glass fiber or PTFE; small-batch cleaning.

Operating Steps

1. Pre-rinse the filter to remove loose pollutants.
2. Place the filter in an ultrasonic cleaning tank filled with water or a low-concentration cleaning agent (5-10% neutral detergent).
3. Set the ultrasonic frequency to 20-40kHz, power to 100-300W, and temperature to 30-50℃; clean for 10-20 minutes.
4. Rinse thoroughly with clean water, air-dry, and inspect for filtration precision recovery.

1. Key Operating Precautions

1. Material Compatibility First:
• PP filters: Avoid strong acids (pH ≤2) and high temperatures (>60℃) during cleaning.
• PTFE/glass fiber filters: Resist most chemicals but avoid high-concentration fluorine-containing acids.
• Seals (EPR/BNR): Avoid oil-based cleaners (use water-based or silicone-compatible agents).
2. Control Cleaning Intensity:
• Backwash pressure ≤0.3MPa (excessive pressure may cause media detachment).
• Chemical concentration and soaking time must not exceed limits (e.g., prolonged acid soaking causes metal framework corrosion).
3. Prevent Secondary Pollution:
• Use clean, filtered water for backwashing/rinsing (avoid tap water with suspended solids).
• Clean the filter housing simultaneously (wipe with neutral detergent, rinse thoroughly) to avoid residual pollutants recontaminating the filter.
4. Post-Cleaning Validation:
• Check pressure drop: Initial pressure drop after cleaning should be ≤80% of the new filter’s initial pressure drop (otherwise, cleaning is ineffective).
• Test water quality: For critical systems (e.g., RO pretreatment), verify post-filtration turbidity/SDI (turbidity ≤0.5NTU, SDI ≤3) to ensure no precision loss.

1. Cleaning Cycle and Frequency

• Backwash: For backwashable systems, perform when pressure drop reaches 0.08-0.1MPa (1-2 times per week for medium-pollution water).
• Chemical Cleaning: Use only when backwash is ineffective; limit to 1-2 times per filter life (frequent chemical cleaning accelerates media aging).
• Abandon Cleaning: If cleaning fails to restore flow rate/pressure drop, or if the filter is cleaned more than 2 times, replace it immediately.

1. Summary

Large-flow filter cleaning is a "supplementary measure" for specific scenarios—physical backwash is preferred for inorganic particle contamination, while chemical cleaning is only suitable for stubborn pollution with compatible materials. Disposable filters should not be cleaned to avoid compromising filtration efficiency and system safety. The core principle is: "Clean only when necessary, replace when ineffective," ensuring stable operation of the filtration system while controlling costs. For critical applications (e.g., petrochemical, pharmaceutical), prioritize replacing filters over cleaning to avoid product quality or equipment failure risks.