Choosing the right industrial filter bag comes down to three decisions: material, micron rating, and size. Get any one wrong and you either clog the bag prematurely, let contaminants through, or waste money on oversized filtration. This guide covers everything a Canadian buyer needs to select, size, and source filter bags for liquid process filtration — from water treatment plants to chemical processing lines.
What Are Industrial Filter Bags and How Do They Work?
Industrial filter bags are porous fabric containers installed inside a bag filter housing. Process liquid enters the housing under pressure, flows through the bag wall, and exits clean on the other side. Contaminants — sediment, particulates, oils, biological matter — collect on the inside surface of the bag until differential pressure rises enough to signal a bag change.
Bag filtration sits between coarse straining (basket strainers at 100+ microns) and fine polishing (cartridge filters below 1 micron). For most industrial liquid applications in Canada — groundwater treatment, parts washing, coolant recycling, food and beverage processing, chemical manufacturing — filter bags handle the bulk removal stage at flow rates from 5 to 200+ GPM per bag.
Bag Filtration vs. Cartridge Filtration
Bag filters handle higher flow rates and larger dirt loads at lower cost per change-out than cartridge filters. Cartridges win on fine filtration (sub-1 micron) and absolute particle retention. Many facilities run bags first to remove the bulk particulate, then cartridges downstream for final polishing — a two-stage approach that extends cartridge life dramatically.
Filter Bag Materials: Which Fabric Fits Your Application?
Material selection depends on chemical compatibility, operating temperature, particle characteristics, and whether you need a disposable or reusable bag. ERE stocks three core materials in the Sampson PLATINUM line:
| Material | Type | Best For | Temp Limit | Reusable? |
|---|---|---|---|---|
| Polypropylene Felt | Depth filtration | General-purpose water, mild chemicals, plating, coolants | 90°C (194°F) | No (disposable) |
| Polyester Felt | Depth filtration | Higher temperatures, aggressive solvents, paints, inks | 150°C (302°F) | No (disposable) |
| Nylon Monofilament (NMO) | Surface filtration | Precise cut-points, reusable applications, food-grade, high-viscosity fluids | 150°C (302°F) | Yes (washable) |
Polypropylene Felt — The Workhorse
Polypropylene is the default choice for industrial liquid filtration in Canada. It resists most acids, alkalis, and aqueous solutions below 90°C. The felt structure creates tortuous paths through the fabric — particles get trapped throughout the depth of the material, not just on the surface. This gives polypropylene felt bags high dirt-holding capacity and long service life at a low unit cost.
Limitation: polypropylene softens above 90°C and degrades in concentrated oxidizers (nitric acid, chromic acid). For high-temperature or solvent-heavy lines, switch to polyester.
Polyester Felt — High Temperature and Chemical Resistance
Polyester felt handles temperatures up to 150°C and resists a broader range of solvents than polypropylene — including ketones, esters, and many organic compounds. It is the standard choice for paint and coating filtration, hot condensate return, and aggressive chemical processing.
Nylon Monofilament (NMO) — Precision and Reusability
NMO bags use a woven mesh rather than a felt matrix. Every opening in the mesh is the same size, which gives NMO bags a sharp, predictable cut-point — particles larger than the rated micron are captured, smaller ones pass through cleanly. This makes NMO the right choice when you need consistent particle classification (food ingredient processing, paint recirculation, resin recovery) rather than maximum dirt loading.
Because the mesh structure doesn't trap particles internally, NMO bags can be cleaned and reused multiple times — a significant cost advantage in high-change-frequency applications. Sampson PLATINUM NMO bags are available from 5 to 1200 microns.
Micron Ratings: How to Choose the Right Filtration Level
The micron rating specifies the size of particles the bag will capture. One micron (µm) equals one-thousandth of a millimetre — a human hair is roughly 70 microns.
| Micron Rating | Captures | Typical Applications |
|---|---|---|
| 1 µm | Fine silt, bacteria-sized particles | Final polishing, pharmaceutical water, electronics rinse |
| 5 µm | Fine sediment, clay | Drinking water pre-treatment, coolant filtration, plating baths |
| 25 µm | Sand, visible particulate | Groundwater treatment, general process water, parts washing |
| 50 µm | Coarse sediment, scale | Cooling tower blowdown, irrigation pre-filter, crude oil/water |
| 100 µm | Large particles, debris | Bulk pre-filtration, pump protection, recirculation straining |
| 200 µm | Coarse straining | Intake protection, debris removal, pre-bag straining stage |
Common mistake: specifying the finest micron available "just to be safe." A 1-micron bag on a 50-micron application will blind almost immediately, spike differential pressure, and require change-outs ten times more often. Match the micron rating to your actual target particle size. If you are unsure, start at 25 µm and adjust based on bag life and downstream quality.
Standard Filter Bag Sizes (#1, #2, #3, #4)
Industrial liquid filter bags follow a universal sizing convention used across all major manufacturers — Pentek, Eaton, Rosedale, and Sampson PLATINUM. Sizing is designated by number:
| Size | Dimensions | Typical Flow Rate | Use Case |
|---|---|---|---|
| #1 | 7" × 17" (178 × 432 mm) | Up to 100 GPM | Standard industrial — most common size |
| #2 | 7" × 32" (178 × 813 mm) | Up to 180 GPM | High-flow or high-dirt-load applications |
| #3 | 4" × 8" (102 × 203 mm) | Up to 25 GPM | Compact systems, lab/pilot, small batch |
| #4 | 4" × 15" (102 × 381 mm) | Up to 50 GPM | Mid-range compact applications |
The bag size must match the housing. A #1 bag fits a #1 housing — there is no cross-compatibility. ERE stocks all four sizes in polypropylene felt, polyester felt, and NMO mesh across the Sampson PLATINUM filter bag range.
Ring Types: Snap Ring vs. Steel Ring
The ring at the top of the filter bag seals it into the housing lid. Two types dominate:
- Snap ring (plastic): Flexible polypropylene ring that snaps into a groove in the housing. Lower cost, lighter, adequate for standard pressures and temperatures.
- Steel ring (carbon or stainless): Rigid ring for high-pressure, high-temperature, or heavy-duty applications. Stainless steel rings are mandatory for food-grade and pharmaceutical installations.
When ordering replacement bags, specify both the bag size and ring type to ensure a proper seal.
Choosing the Right Bag Filter Housing
The filter bag is only half the system — the bag filter housing determines flow capacity, pressure rating, connection size, and material compatibility. ERE offers Sampson housings in several configurations:
- Single-bag housings: The standard for most industrial lines. Stainless steel 304/316L construction, available with threaded or flanged connections. Suitable for flows up to 100 GPM with a #1 bag or 180 GPM with a #2 bag.
- Multi-bag housings: For high-flow applications (200–1000+ GPM) where a single bag cannot handle the volume. Multiple bags operate in parallel inside a single vessel. ERE carries the Sampson Multi-Bag Housing and the Shelco BFS Series.
- High-pressure housings: Rated for systems exceeding 150 PSI. The Sampson High Pressure Housing handles demanding applications in chemical processing and oil and gas.
- Duplex housings: Twin-vessel systems with a transfer valve that allows bag changes without stopping flow — critical for continuous process lines.
Common Applications by Industry
- Water and wastewater treatment: Pre-filtration for RO membranes, well water sediment removal, stormwater treatment, cooling tower blowdown
- Food and beverage: Wine, beer, juice, syrup, and edible oil clarification (NMO bags, food-grade stainless housings)
- Chemical and petrochemical: Process chemical filtration, solvent recovery, resin capture (polyester felt for solvent resistance)
- Automotive and manufacturing: Coolant recycling, parts wash water, paint booth water, electrocoat filtration
- Mining and minerals: Process water clarification, tailings treatment, reagent filtration
- Pharmaceutical and electronics: Ultra-pure water pre-filtration, DI water polishing (1 µm felt + downstream cartridge)
- Environmental remediation: Groundwater treatment systems, pump-and-treat pre-filtration, oil/water separator pre-straining
Need help selecting filter bags for your application?
ERE Inc. has been Canada's environmental and industrial filtration specialist for over 30 years. Our team can recommend the right material, micron rating, and housing configuration for your process — no obligation.
→ Request a Quote | 1-888-287-EREC | Browse Filter Bags | sales@ereinc.com
Frequently Asked Questions
What size are industrial filter bags?
Industrial liquid filter bags come in four standard sizes: #1 (7" × 17"), #2 (7" × 32"), #3 (4" × 8"), and #4 (4" × 15"). Size #1 is the most common and fits housings rated up to 100 GPM. The bag size must match the housing — there is no cross-compatibility between sizes.
How often should you change a filter bag?
Replace filter bags when differential pressure across the housing reaches the manufacturer's recommended maximum (typically 15–25 PSI for most liquid bag housings). In practice, change-out frequency depends on dirt loading — some applications need weekly changes, others run for months. Monitor your pressure gauges rather than relying on a fixed schedule.
Can you wash and reuse filter bags?
Nylon monofilament (NMO) bags can be cleaned and reused multiple times because their woven mesh structure does not trap particles internally. Felt bags (polypropylene and polyester) are single-use — once the felt matrix loads with contaminants, cleaning cannot restore original performance.
What is the difference between felt and mesh filter bags?
Felt bags (polypropylene, polyester) use a non-woven depth-filtration structure that traps particles throughout the fabric thickness. They offer high dirt-holding capacity but are not reusable. Mesh bags (NMO) use a woven structure with uniform openings for a precise micron cut-point and can be washed and reused, but hold less total dirt per cycle.
Related articles
- Bag Filter Housings: Complete Sizing and Selection Guide
- Filter Bag Sizes: Standard Dimensions, Rings, and Compatibility
- Polypropylene vs. Nylon vs. Polyester Filter Bags
- Multi-Bag vs. Single-Bag vs. Duplex Filter Housings
- Filter Bag Micron Ratings: How to Choose
Lire en français : Sacs filtrants industriels : guide complet de sélection au Canada