How to select water filter bags suitable for specific water treatment needs?

I. Clarify water quality and treatment objectives

1. Analyze water source impurity characteristics

• Particle types: Suspended solids (e.g., sediment, rust), colloids (e.g., clay, microorganisms), oils, or specific pollutants (e.g., metal ions, organic matter).
• Particle size: Determine the main impurity particle size range through water quality testing (e.g., coarse particles >50 microns, fine particles <10 microns).
• Chemical properties: Liquid acidity/alkalinity (pH value), corrosiveness (e.g., chloride ions, strong oxidizers), and temperature (normal or high-temperature environments).

2. Define filtration goals

• Precision requirements: Target filtration accuracy (e.g., drinking water ≤5 microns, industrial circulating water up to 50 microns).
• Treatment volume: Water flow rate per unit time (e.g., 10 m³/h, 100 m³/h), affecting filter bag size and quantity.
• Impurity interception capacity: Concentration of contaminants to be intercepted (high-turbidity water sources require high dirt-holding capacity filter bags).

II. Core selection parameters

1. Filtration precision (critical parameter)

• Precision range: Common filter bag precisions range from 1–500 microns, selected based on impurity particle size.Note: Excessively high precision may cause rapid clogging; balance filtration efficiency with flow rate.
  • Examples:
    • Swimming pool water filtration: 20–50 microns (removes hair, sediment).
    • Pre-treatment for electronic-grade ultrapure water: 1–5 microns (intercepts tiny particles).
    • Chemical wastewater oil removal: 10–25 microns (paired with demulsification processes).

2. Material compatibility

• Common materials and applications:

  Material	Corrosion resistance	Temperature resistance	Typical applications
  Polypropylene (PP)	Resistant to acids, alkalis, salt solutions	≤80℃	Industrial wastewater, municipal sewage, food processing
  Polyester (PET)	Resistant to oil and general solvents	≤120℃	Lubricating oil filtration, oily wastewater treatment
  Nylon (PA)	Resistant to strong alkalis, wear-resistant	≤90℃	High-turbidity water sources, metalworking fluid filtration

• Selection principles:
  • Choose PP material for acidic liquids and PA or PET for alkaline liquids.
  • Select PET or special high-temperature-resistant fibers for high-temperature environments (e.g., boiler water).

3. Filter bag size and structure

• Specification categories:
  • No. 1 bag: Diameter 110mm, length 380mm, flow rate ~5–15 m³/h (common in small systems).
  • No. 2 bag: Diameter 180mm, length 810mm, flow rate ~20–50 m³/h (mainstream for medium-to-large systems).
  • Others: No. 3 bags, No. 4 bags, or non-standard custom sizes.
• Structural design:
  • Monofilament filter cloth: Smooth surface, easy to clean, suitable for intercepting large particles (coarse filtration).
  • Multifilament/needle-punched filter cloth: Deep filtration, high dirt-holding capacity, suitable for fine particle filtration.
  • Reinforced ring design: Stainless steel or plastic rings at the top to prevent bag mouth tearing and improve pressure resistance.

4. Pressure resistance and flow matching

• System pressure: Filter bags must withstand ≥ system operating pressure (typically 0.1–0.6MPa); use thickened materials or metal frame supports for high-pressure scenarios.
• Flow calculation:
  • A single No. 2 bag at 50-micron precision has a flow rate of ~30 m³/h; for a 100 m³/h system, parallel 4 bags (with redundancy).

III. Other key factors

1. Dirt-holding capacity and replacement cycle

• Dirt-holding capacity: Total amount of impurities a filter bag can retain (unit: g/bag); high capacity reduces replacement frequency.
• Estimation method:
  • For known suspended solids concentration (e.g., 500 mg/L) and total treatment volume (e.g., 1000 m³), total impurity weight = 500 mg/L × 1000 m³ = 500 kg.
  • If a single filter bag holds 5 kg, it needs to be replaced 100 times per cycle, or increase the number of filter bags to reduce frequency.

2. Environmental protection and cost

• Disposable vs. washable:Material recyclability: Prioritize recyclable PP/PET materials to reduce plastic pollution.
  • Disposable filter bags: Low cost (~¥10–50/bag), suitable for complex impurities or non-washable scenarios.
  • Washable filter bags: Higher cost (~¥200–500/bag) but reusable, ideal for high-value liquids or strict environmental requirements.

3. Compatibility with supporting equipment

• Filter type: Must match filter bag size (e.g., No. 1 bag for small filters, No. 2 bag for standard filters).
• Sealing method: O-ring or flange sealing to ensure no leakage.

IV. Selection process example

1. Precision selection: Intercept particles >20 microns, choose 25-micron precision filter bags.
2. Material selection: Neutral water, choose economical and durable PP material.
3. Size selection: Single No. 2 bag flow rate 30 m³/h, require 2 bags in parallel (total flow 60 m³/h to cover 50 m³/h demand).
4. Structure selection: Needle-punched filter cloth (deep filtration, high dirt-holding capacity) with stainless steel reinforcing rings.
5. Replacement cycle: Estimated daily treatment volume 400 m³, inlet suspended solids concentration 200 mg/L, daily impurity total 80 kg; single bag dirt-holding capacity 5 kg, requires daily replacement of 2 bags (or replace every 2 days with spare bags).

V. Notes

1. Testing and verification: For high-requirement scenarios (e.g., pharmaceuticals, electronics), test with sample filter bags first to confirm filtration efficiency and service life.
2. Supplier qualification: Choose ISO-certified manufacturers to ensure filter bags meet hygiene standards (e.g., food-grade requires FDA certification).
3. Emergency plans: Stock spare filter bags to avoid system downtime; regularly inspect for damage (replace immediately if pressure drop surges).