Where it fits
The standard liquid bag is the workhorse consumable for high-flow pre-filtration. Size codes #1 to #4 are the industry-wide bag standard, so they drop straight into mainstream housings and changing supplier does not mean changing hardware. Ambient pure water, hot aggressive chemistry and viscous feeds all sit inside its range.
Key characteristics
What actually drives selection is the media, not the bag shape: needle-felt polypropylene and polyester cover general duty, monofilament nylon mesh covers sieving where a particle-size cut matters, and PTFE and aramid are held in reserve for heat and aggressive chemistry. One set of dimensions, and changing media changes the whole temperature window — the flexibility a cartridge cannot match.
The seam choice is a real trade-off. A seamless welded bag has no needle holes to bypass through and is the right call at fine ratings; a fully sewn body with a reinforced bottom is stronger and takes the impact load of viscous fluids. Needle felt is nominally rated, typically around eighty to ninety percent single-pass removal at the stated rating, and treating that as absolute will cause trouble.
Choosing between options
How the four bags on this site divide the work:
| Bag | Filtration mechanism | Rating range | Choose it when |
|---|---|---|---|
| Standard liquid bag (this) | Needle-felt depth, mesh optional | 0.5 – 1000 µm | High-flow pre-filtration, widest media choice, cost per bag first |
| High-performance absolute bag | Melt-blown microfibre, graded pores | 0.2 – 20 µm | An absolute rating is required, or bags are replacing a bank of cartridges |
| High-strength nylon bag | Monofilament mesh, fixed-aperture surface filtration | 50 – 400 µm | A clean particle-size cut is needed and the bag will be washed and reused |
| Plating anode bag | A sleeve hung on the anode itself | 25 – 100 µm | Holding back anode sludge, not fitted in a housing basket |
Operation & change-out
A bag is always used inside a support basket. Recommended flow is quoted on clean water, and fine ratings at 5 µm and below should be derated to fifty or sixty percent of it. Change on whichever arrives first, the differential threshold or the flow decay limit. Standard bags are silicone-free and safe upstream of coating and plating lines.