Buyer guide · Updated 22 Oct 2026 · By the Filtsap technical team
How to choose a bag filter: size, micron and material
Short answerTo choose a bag filter, match four things: bag size (flow rate), micron (particle size), material (chemical and temperature compatibility) and housing. A standard #2 bag (7" × 32") handles about 20–40 m³/hr of water. PP felt suits most chemicals up to 90 °C. Nylon mesh is reusable and gives an exact micron rating.
Standard bag sizes
| Size | Dimensions | Approx. water flow |
|---|---|---|
| #1 | 7" × 16" (180 × 420 mm) | 10–20 m³/hr |
| #2 | 7" × 32" (180 × 810 mm) | 20–40 m³/hr |
| #3 | 4" × 8.25" | 3–6 m³/hr |
| #4 | 4" × 14" | 6–12 m³/hr |
For viscous liquids (oil, syrup, paint), size the bag at a third to half of the water flow figure.
Material selection
| Material | Strength | Max. temp |
|---|---|---|
| PP needle felt | Acids, alkalis, solvents; cheap depth filtration | ~90 °C |
| Polyester felt | Oils, paints, higher temperature | ~150 °C |
| Nylon monofilament mesh | Exact micron, washable, reusable | ~150 °C |
Single or multi-bag housing?
One #2 bag is enough for most lines up to about 30 m³/hr. Above that, use a multi-bag SS housing, or two housings in duplex so you can change bags without stopping the line.
Browse filter bags → · Bag filter housings →
FAQs
How often should I change a filter bag?
Change it when the differential pressure reaches 1–1.5 bar (15–22 psi). Letting it climb higher can burst the bag.