Security Filter Design and Calculation Selection

Security filters are mainly used to remove small particles (such as suspended solids, colloids, microorganisms, etc.) from liquids, protecting downstream equipment (such as Reverse Osmosis Membranes, ion exchange resins, etc.). Their design and selection require comprehensive consideration of factors such as fluid properties, filtration accuracy, flow rate, pressure drop, and material compatibility. The following are the core steps and key points of design and calculation selection:

I. Design Steps

1. Define Filtration Requirements

Filter Media: Liquid (water, oil, chemical solution).

Target Contaminants: Particle type (e.g., silt, rust, microorganisms), particle size range, concentration.

Filtration Accuracy: Typically 1~100 microns (commonly 1μm, 5μm, 10μm), determined according to downstream equipment requirements.

Flow Rate Requirements: Maximum/Minimum flow rate (m³/h or L/min).

Operating Conditions: Temperature, pressure (working pressure and maximum withstand pressure), pH value, chemical compatibility.

2. Selecting the Filter Type

Cartridge Filter: Suitable for high-precision, low-flow scenarios (e.g., reverse osmosis pretreatment).

Bag Filter: Suitable for high-flow, medium-precision (10~100μm).

Candle Filter: Suitable for media with high viscosity or high solids content.

Self-Cleaning Filter: Suitable for scenarios requiring high automation and minimal maintenance.

3. Material Selection

Filter Cartridge: Polypropylene (PP), Polytetrafluoroethylene (PTFE), Nylon, Sintered Metal.

Shell Material: Stainless Steel (304/316L), Carbon Steel (with anti-corrosion lining), PP/UPVC (corrosion resistant).

Sealing Material: EPDM, Silicone, Fluororubber (selected according to the chemical properties of the media).

4. Determining Filter Cartridge Parameters

Filter Area: Determines dirt holding capacity and pressure drop; requires flow rate calculation.

Filter Cartridge Length: Standard sizes are 10 inches, 20 inches, 30 inches, and 40 inches.

Connection Type: Chuck type, threaded type, flange type.

II. Selection Considerations

Filtration Accuracy Matching: Downstream equipment requirements: For example, reverse Osmosis Systems require an accuracy of less than 5μm. Actual Particle Distribution: Select an appropriate accuracy level through particle counter testing.

Flow Rate and Pressure Drop Balance: Excessive flow rate may lead to excessive pressure drop or shortened filter cartridge life. Select the number and area of ​​filter cartridges based on system pressure limitations.

Chemical Compatibility Verification: Filter media and sealing materials must be resistant to media corrosion. Corrosion (Refer to the chemical compatibility table).

Maintenance and Cost Optimization: Filter Replacement Frequency: For high-contamination scenarios, choose large-capacity filters or self-cleaning designs. Economy: Compare the long-term costs of disposable and washable filters.

III. Precautions

Pre-filtration Protection: Install a coarse filter (e.g., 100μm) before the security filter to extend filter life.

Exhaust and Drainage: The housing design must include exhaust and drain valves to avoid air blockage and sedimentation.

Validation Testing: Pass the bubble point test (to verify filter integrity) and particle rejection rate test.

Safety Margin: It is recommended to have 10%~20% more filter cartridges to cope with sudden contamination or flow fluctuations.